The Project Gutenberg EBook of Natural History of the Racer Coluber
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Title: Natural History of the Racer Coluber constrictor
Author: Henry S. Fitch
Release Date: May 10, 2013 [EBook #42676]
Language: English
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Transcriber's Notes
Emphasis denoted as _Italics_.
[M] and [F] represents the male and female symbols respectively.
Whole and fractional parts of numbers are represented as 41-3/4.
===================================================
University of Kansas Publications
Museum of Natural History
----------------
Volume 15, No. 8, pp. 351-468, pls. 19-22, 20 figs.
----------------- December 30, 1963 ----------------
Natural History of the Racer
Coluber constrictor
BY
HENRY S. FITCH
University of Kansas
Lawrence
1963
University of Kansas Publications, Museum of Natural History
Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Theodore H. Eaton, Jr.
Volume 15, No. 8, pp. 351-468, pls. 19-22, 20 figs.
Published December 30, 1963
University of Kansas
Lawrence, Kansas
PRINTED BY
JEAN M. NEIBARGER, STATE PRINTER
TOPEKA, KANSAS
1963
[Illustration]
29-7864
Natural History of the Racer Coluber constrictor
BY
HENRY S. FITCH
CONTENTS
PAGE
Introduction 355
Acknowledgments 357
Methods and Materials 358
Description 362
Color pattern 362
Bodily proportions 365
Lepidosis 367
Dentition 369
Hemipenis 369
Relationships 370
Range 371
Geographic Variation 373
Habitat 375
Temperature Relationships 377
Home Range and Movements 385
Food Habits 394
Methods of obtaining prey 394
Composition of food 395
Kinds of prey 403
Reproduction 408
Sexual behavior 408
Cycle of the male 414
Eggs 416
Hatching 423
Growth 425
Mortality Factors and Adaptations for Survival 432
Defense and escape 432
Natural enemies 438
Disease 442
Parasites 442
Populations 445
Composition 445
Numbers 450
Summary 456
Literature Cited 461
Introduction
Throughout much of the United States the racer is abundant and is one
of the snakes best known to man. Its active diurnal habits and its
preference for a habitat in meadows, pastures, and hayfields rather
than in remote wilderness areas, result in frequent encounters with
humans. The racer is a predator on many kinds of small animals, both
vertebrates and invertebrates; it takes as food chiefly animals that
are agricultural pests but also destroys some beneficial kinds. Yet,
in general, the attitudes of rural people toward the racer are little
influenced by these economic and ecologic considerations, but rather,
are dominated by an unreasonable fear, despite the racer's inoffensive
disposition, and inability to inflict any harm on humans.
Although an extensive literature exists regarding the racer, no
thorough study of the species' natural history has been made
heretofore. Obviously such study is needed. Few species of vertebrates
having comparable economic bearing have been similarly neglected. In
1948, undertaking a program of ecological research on the recently
created University of Kansas Natural History Reservation, I included
the racer among the many common species studied to gain insight into
the functioning of the local ecosystem. Live-trapping of snakes on the
area was begun in 1949, and these operations were greatly intensified
in the years 1957 through 1962, with efforts concentrated on the study
of the racer in the 1960, 1961 and 1962 seasons. Thus my study is
based upon 14 consecutive years' records on the Reservation, the
northeasternmost section in Douglas County, Kansas, six and one-half
miles north northeast of the University of Kansas campus at Lawrence.
After the acquisition in 1956 of the 160-acre Rockefeller Tract
adjacent to the Reservation on the north in Jefferson County, field
work was extended to this new area, which, because it was superior
habitat, in the final years of the study produced more records than
the Reservation. An important but relatively minor segment of the data
originated from Harvey County Park, 13 miles west of Newton, Kansas,
where lines of live-traps were maintained in 1959, 1960, 1961, 1962.
Smaller collections of data were obtained from the Lalouette Ranch in
the Flint Hills, three miles northeast of Florence, Marion County,
Kansas, and from Cedar Bluff Reservoir, 23 miles west and seven miles
south of Hays in Trego County, western Kansas, where live-trapping was
carried on in 1959 and 1960. Additional data were obtained on
numerous field trips to various collecting localities in northeastern
Kansas. My first-hand knowledge of the species is also based, in part,
on many years of field experience with the far western subspecies _C.
c. mormon_ in western Oregon and California, and on similar experience
in 1947 and 1948 with the southern subspecies, _C. c. anthicus_ in
central Louisiana.
This varied field experience with the species at localities well
scattered throughout its geographic range has added perspective to the
study even though most of the records were collected within a radius
of three quarters of a mile. No one locality can be regarded as
entirely typical of a species' habitat over its range as a whole.
According to my philosophy, the ecological niche of a species is
subject to geographical variation analogous to the variation to be
seen in the morphological characters of the animal itself. Different
community associates, including different competitors, prey, and
predators, and different physical factors enforce a somewhat different
way of life on a species in geographically remote parts of its range.
When analyzed these differences often turn out to have a genetic
basis. Thus, limits of tolerance to heat, cold, and drought often vary
geographically, and the population density, reproductive potential,
seasonal cycle, and other properties of populations may be altered
either by the direct effect of the environment, or through its effect
on the genetic constitution, produced by natural selection.
The local population of racers studied was near the center of the
species' geographic range, and is to some extent representative of the
species as a whole, though differing in its ecology from other
populations in proportion to their remoteness and the distinctness of
their habitats. It has not been demonstrated that ecological traits of
populations change in a discontinuous manner or correspond in their
limits with those of named subspecies. More likely geographical
variation is continuous and parallels morphological variation only in
a general way. Certainly the boundaries of subspecies' ranges should
not be accorded undue emphasis in an ecological study.
My investigation of the blue racer under natural conditions, combined
with a compilation and analysis of published literature, has resulted
in a fairly satisfactory understanding of some phases of the species'
ecology and natural history, such as the food habits, the growth rate,
the extent of home range and of seasonal movements. However,
relatively little was learned concerning some phases of the life
history. Unfortunately, the traps used did not catch young of the
smaller sizes. Facts concerning egg-laying, incubation, and hatching
therefore are known chiefly from snakes kept in confinement. Although
first-year young were captured by hand from time to time they were
obtained in relatively small numbers, and little was learned regarding
their population density, movements, or mortality factors. Of course,
such hiatuses are to be expected; even in man such enigmas as the
disparate sex ratio still challenge the investigator.
For the subspecies of racer involved in my field study the widely used
vernacular "blue racer" has been adopted in this report. In general I
advocate conformity with the vernacular names published by the
Committee on Herpetological Common Names (1956). However, in this
list, the name blue racer was assigned to _Coluber constrictor foxi_,
an invalid subspecies of the Prairie Peninsula that has been relegated
(Auffenberg, 1955:92; Smith, 1961:196) to the synonymy of _C. c.
flaviventris_. It therefore seems appropriate that the book name
"yellow-bellied racer" applied to _flaviventris_ by the Committee
should be abandoned for this subspecies, and that the name blue racer
be applied officially, as it is in actual practice by both laymen and
herpetologists, to all populations of this subspecies.
Acknowledgments
Financial assistance from the National Science Foundation in 1957
through 1962 is acknowledged. Although none of the three separate
grants involved was made specifically for the autecological study of
the racer, all three contributed to the support of the extensive
program of live-trapping for snakes, which yielded most of the records
upon which this report is based. Student assistants who were employed
on these projects include James W. Bee, William N. Berg, Donna M.
Hardy, Robert M. Hedrick, Dale Hoyt, Robert M. Packard, Robert G.
Webb, and Wayne Wiens, at the Reservation; Roy Henry, Dale Horst,
Dwight R. Platt, and Howard L. Schrag at Harvey County Park, and
Gilbert L. Adrian at Cedar Bluff Reservoir. Dr. Edwin P. Martin,
formerly of Fort Hays, Kansas State College, was helpful in planning
and carrying out the field work at Cedar Bluff Reservoir. Eric
Shulenberger assisted with field work and processing of data in 1962
under the National Science Foundation program for Undergraduate
Research Participation. Robert Miner assisted with the examination of
specimens in 1960. Mr. August Lalouette of Florence, Kansas, permitted
field work on his ranch and contributed information and materials to
expedite this work. Mr. and Mrs. Harold Brune of Route 3, Lawrence,
Kansas, kindly contributed several clutches of racer eggs found on
their farm in Jefferson County, and also made available significant
information accompanying them. Dr. William H. Stickel kindly made
available at my request records of predation on racers from the food
habits files of the U. S. Fish and Wildlife Service. Dr. William E.
Duellman of the University of Kansas Museum of Natural History and Dr.
Robert C. Stebbins of the University of California Museum of
Vertebrate Zoology kindly permitted examination and dissection of
specimens in the collections under their care. Dr. George W. Byers of
the University of Kansas Department of Entomology identified numerous
insects eaten by racers. My daughter, Alice V. Fitch, often assisted
me with the field work and the processing of data. My wife, Virginia
R. Fitch, read the manuscript critically, assisted me with the
examination of museum specimens, and with typing, and helped in
various other ways.
Methods and Materials
Table 1. Numbers and Distribution of Captures and Recaptures of Blue
Racers on the Reservation and Rockefeller Tract
=======================+=========================+=======================
Span of years within | Number of separate | Number of times
which each individual | years within which each | each individual
was captured | individual was captured | was captured
---------+-------------+-----------+-------------+----------+------------
| | | | Times |
Years | Individuals | Years | Individuals | captured | Individuals
---------+-------------+-----------+-------------+----------+------------
1 | 749 | 1 | 749 | 1 | 679
2 | 137 | 2 | 197 | 2 | 181
3 | 56 | 3 | 51 | 3 | 93
4 | 32 | 4 | 15 | 4 | 31
5 | 19 | 5 | 6 | 5 | 7
6 | 13 | 6 | 1 | 6 | 14
7 | 7 | 7 | 0 | 7 | 8
8 | 2 | 8 | 1 | 8 | 4
9 | 3 | | | 9 | 1
10 | 0 | | | 10 | 0
11 | 1 | | | 11 | 0
12 | 1 | | | 12 | 1
| | | | 13 | 0
| | | | 14 | 0
| | | | 15 | 0
| | | | 16 | 1
---------+-------------+-----------+-------------+----------+------------
This investigation was based primarily on the capture in live-traps,
marking, release, and recapture of blue racers in their natural
habitat. On the combined area of the Reservation and the Rockefeller
Experimental Tract, 1020 blue racers were recorded a total of 1688
times from August 30, 1948, to October 27, 1962. At Harvey County Park
361 blue racers were marked, and were captured a total of 467 times
from May 6, 1959, to September 14, 1962, and at Cedar Bluff Reservoir
42 were captured from May 11, 1959, to June 30, 1960.
The traps used were cylinders of galvanized wire, "hardware cloth"
(Fitch, 1951:77; 1960:77), having funnels opening into each end, or
having a funnel at one end and a plug at the other. The traps, open at
both ends, were used along hilltop rock ledges where an exposed
vertical rock face provided a barrier along which a snake might travel
and where it could be easily intercepted by the trap without any
accessory equipment (see Pl. 21, Fig. 1). Where such natural barriers
were lacking, as in level fields, barriers consisting of boards,
screens or sheet metal were installed to guide the racer toward the
trap and into a funnel entrance. Two such barriers at each end of a
trap forming a V to guide the snake into the funnel were used in 1956
and 1957, when trapping at places away from the hibernation ledges was
undertaken. Later it was found simpler and more effective to use a
single barrier with a trap at each end. The barrier extended up into
the funnel entrance, and usually the racer, following along the
barrier on either side, would pass into the funnel and through its
apex. However, it was possible for a racer to travel around the end of
the barrier without entering the trap, and perhaps some did so.
The need for making the barrier and trap a tight unit impassable to
the snake, was somewhat counterbalanced by the need for having the
whole installation loosely constructed so that it could be easily
altered, opened, adjusted, and cleaned. Since the traps were kept set
in large numbers, and the task of checking them was time-consuming,
speed of operation was more important than the perfect functioning of
any one trap. Approximately 200 traps were kept set when operations
were at their maximum. No record was kept of the number of "trap days"
involved in the study, but the total was well over 100,000 for the
Reservation and the Rockefeller Tract. When traps were set at both
ends of a barrier, the outer end of each trap was closed with a plug.
No bait was used in the traps. Occasionally small vertebrates and
insects of kinds used as food by the racers may have gotten caught
first and served to attract the snakes. Best catches of racers were
made in the breeding season, since males were attracted by females
already in the traps, and several males might be captured
simultaneously with one female. Occasionally as a person approached or
handled a trap, a racer darted out of it, displaying a perception,
acuity of vision, and skill in avoiding the inward projecting wire
prongs encircling the small funnel opening, that were exceptional
among the several species of snakes trapped. Doubtless many other
racers that were caught in traps escaped before they were discovered.
If the funnel entrance of the trap was of the same diameter as the
snake itself, or only a little larger, there was little likelihood of
the trapped racer escaping. However, funnel openings were usually
adjusted at a diameter of approximately 1-1/4 inches, allowing an
ample margin for even the largest racers, though inadequately small to
permit ingress of a few of the largest black rat snakes, bull snakes
and timber rattlers occurring locally.
Ordinarily the snakes trapped were processed in the field and released
immediately. The method of marking was essentially that of Blanchard
and Finster (1933:334). Two subcaudals, one on the right side and one
on the left, were clipped on each snake, and when these marks healed
they left permanent scars. In the racer, as in most other colubrines,
the subcaudals are divided into a double series, one on the left and
one on the right. Scales of the left and right sides are placed
alternately. At the base of the tail one or more undersized scales
usually are present on each side, and there might be some question as
to precisely where the count should begin. The rule followed was to
exclude from the count any small basal scales on either side that did
not extend medially to contact at least one scale of the opposite
side. The scale designated as "one left" (or "one right") was the
first to contact one of the opposite series, regardless of whether the
former was of normal size or (as was usually the case) smaller and
narrower than those following it. In marking, this "number one" scale
was never clipped but was left as a point of reference since a base
mark was needed from which to begin the count. The marks were read
from left to right, for example U 5_l_ 2_r_, the "U" referring to the
subcaudals or "urosteges," the "5_l_" indicating the fifth on the left
side, and "2_r_" indicating the second on the right. The subcaudals
clipped were the first 19 following the basal scale. When the 361
possible combinations all had been used, ending with U 20_l_ 20_r_, a
new series was begun duplicating the first except that on each snake
the first ventral (or "gastrostege") anterior to the anal plate was
clipped on the left side (G1L) to distinguish these snakes from the
series previously marked. Later, a third series, "G2R" was marked,
and eventually a fourth series, "G3L" was started.
There were many borderline instances in which the basal scale barely
contacted one of the opposite side. In such instances the formula was
written U 5_l__{ISB} 2_r_, the subscript ISB signifying "including
small basal." In other instances a basal subcaudal barely failed to
contact a scale of the opposite side and this condition was indicated
by the subscript NSB--"not including small basal." The condition might
be so nearly equivocal that on successive occasions the same formula
might be read U 5_l__{ISB} 2_r_ and U 4_l__{NSB} 2_r_. Occasional
misidentifications of individuals that resulted from such
discrepancies were in most instances readily detected when the field
records were transferred to individual file cards where the sex, size,
and location of the snake at its previous captures were shown.
In some instances racers recaptured after periods of years retained
conspicuous scars where scales had been clipped, but in other
instances the marks had become obscure, and in fact the only trace of
a mark might be a slight narrowing or notching of part of the scale
originally clipped. Snakes caught and marked early in life probably
retained more power of regeneration than those clipped after the
attainment of maturity, but otherwise the basis for difference in
extent of regeneration was not evident. In the same snake, three
scales, all clipped on the same day, might show much different degrees
of regeneration after the lapse of a year or more. In general,
obscuring of marks by regeneration was a source of inconvenience
rather than of error; only a negligible percentage of the recaptured
racers had marks so obscure that their identities might have been
seriously questioned, and it is doubtful that any marks were lost
completely by regeneration.
Racers found in traps were removed, measured (snout-to-vent length,
tail length), weighed in a cloth bag suspended from spring scales, and
marked. The mouth was forced open and the snake was examined for
flukes. Enamel paint of a bright color, red, green, yellow, blue or
orange was smeared on the snake to gain information regarding the time
of molt. The stomach was palpated for recently ingested food items,
and any detected were forced up into the gullet to be identified, then
were squeezed back into the stomach. The rear part of the body was
palpated to detect undigested material in the gut, and if any was
present, an attempt was made to squeeze out the fecal material, using
only light pressure, with care not to injure the racer. The inside of
the trap and the ground beneath it were inspected for fecal material
that might have been voided while the snake was confined. Any
scatological material obtained was wrapped in a paper towel, labelled
and brought back to the laboratory where it was stored. Eventually
each scat was soaked for a day or more in a detergent solution, rinsed
in running water in a fine gauze bag, dried, and placed with its label
in a cellophane envelope for subsequent microscopical study.
Various items concerning reproductive condition were also routinely
recorded. In females the ventral surface was palpated at the rear end
of the body to detect the genital bursa or vagina, which in sexually
mature individuals has a much thickened wall, and can be felt as a
distinct lump. Males were likewise tested for sexual maturity by
pipetting a small amount of fluid from the cloaca into a vial and
returning it to the laboratory where it was examined microscopically
for motile sperm. Also, sperm samples were often taken from males at
different times throughout the season of activity, and cloacal samples
from females occasionally were checked for sperm as evidence of recent
copulation.
In the summer of 1962 an outdoor enclosure of 100-foot circumference
was constructed, of galvanized sheet iron, with wall three feet high,
set on a concrete base extending to a depth of two feet. A
two-foot-deep concrete basin inside the enclosure served as a water
container. The enclosure was partly shaded by a large walnut tree and
the area enclosed had lush vegetation, including brome grass, various
shrubs, and young trees up to 15 feet high, thus including most
features of the racers' habitat, and it was situated in an area
frequented by the snakes. Throughout the summer several racers were
kept in the enclosure, and frequent observations on them yielded much
information concerning time of activity, temperature preferences, and
social and sexual behavior that could not have been obtained readily
either from racers confined in small cages or from those free under
natural conditions.
Description
_Color Pattern_
Hatchling racers differ much in appearance from adults; whereas the
latter are of dull uniform coloration dorsally, the hatchlings have a
checkered pattern of alternating blotches in several rows, including a
middorsal row, with blotches much larger than those of the other
rows. This basic pattern is perhaps the most common one in all snakes,
and is found in the young of various other genera (notably _Elaphe_)
which lose or alter their markings during development. In these genera
and in the racer, the juvenal checkered pattern may represent
recapitulation of an ancestral condition. The adaptive significance of
having a blotched, checkered pattern in the young, and uniform
coloration in the adult is not evident. I have rarely seen the
hatchlings under natural conditions except by finding them hiding
beneath flat rocks. Their concealing pattern must be fully as
effective as that of adults and the young themselves are more
secretive than the adults.
A hatchling of 240 millimeters snout-vent length was described as
follows on September 22, 1962: Ground color pale olive anteriorly,
gradually darkening posteriorly, marked with chocolate blotches;
middorsal blotches largest averaging about five scales long and seven
or eight scales wide anteriorly; posteriorly, blotches become less
distinct (tending to blend into progressively darkening ground color),
and width-to-length ratio increases; gradual obscuring of blotches
proceeds posteriorly, until on tail they can no longer be
distinguished, and color is uniformly olive; on each side, row of
lateral blotches alternates with that of middorsal blotches; lateral
blotches average somewhat less than two scales long, and approximately
two scales wide and are of irregular shape, sometimes subdivided;
farther down on sides, lower row of lateral blotches alternates with
upper lateral row; this lower lateral row, approximately same size as
upper lateral row, and situated at level of first scale row,
overlapping onto ventrals, where it pales to reddish brown; almost
every ventral scute has one pair or more of dark reddish brown spots,
tending toward semicircular shape, the arc of each projecting forward,
but posteriorly on body these spots become increasingly obscure, and
are indiscernible on posterior end of body and on tail; ventral
surface white on chin and throat, gradually assuming suffusion of pale
greenish gray posteriorly; eye dark with narrow yellowish margin
around pupil; top of head grayish olive, mottled with faint and
irregular dark markings; supralabials whitish, with chocolate
markings, mostly wedge-shaped, in their posterior parts; rostral and
internasals edged with dark posteriorly; posterior upper corner of
loreal and adjacent corner of prefrontal dark; temporals having dark
markings; chin almost immaculate, but with narrow black posterior
edges on some of the infralabials (see Plate 19, Figs. 1 and 2, and
Plate 20, Fig. 2).
The checkered pattern of the juvenile fades gradually as development
proceeds. Persistence of the juvenal markings varies greatly in
individuals and probably is subject to geographic variation also. By
the time sexual maturity is attained the dorsal pattern often is
indiscernible or represented only by faint traces. The ventral
speckling is more persistent.
A female of 602 millimeters snout-vent length in mid-July 1962, at a
probable age of 11 months, was described as follows: Overall dorsal
color olive gray, but with remnants of juvenal pattern discernible;
dark dorsal blotches have almost faded, but their edges, about one
scale wide, are still distinct; low on sides, color fades to pale
bluish gray, and to pale greenish blue on edges of ventrals; on
anterior one-third of body midventral surface is lemon yellow; farther
posteriorly it fades to ivory, almost white on tail; chin white,
except for reddish brown posterior edges of last infralabials, and
streak of same color on each antepenultimate infralabial; top of head
olive gray with irregular scattered dark marks; preoculars pale
centrally with olive brown edges; supralabials white with reddish
brown triangular marks; postnasals white anteriorly, gray posteriorly;
uppermost postocular brownish orange, paler centrally; two rows of
semicircular spots on belly, distinct anteriorly, but fading
posteriorly until indiscernible on posterior part of belly; numerous
small black spots scattered irregularly over dorsal and lateral
surfaces.
A male racer retained more of the juvenal pattern at an approximate
age of 15 months, when he was described on November 30, 1961: Dorsal
surface dark grayish brown, the large juvenal dorsal blotches (each
about eight scales wide) easily discernible, but faint; top of head
dark olive brown, mottled with black, paling in rostral region;
supralabials white on their anterior and lower portions, marked with
brown and blue-gray on their upper and posterior portions; chin white,
but with rusty markings on last four infralabials; ventrals
ivory-yellow with rusty spots of which the largest are approximately
three-fourths of the ventrals' breadth; first row of scales bluish
gray, or with greenish suffusion (in neck), most of scales having
indistinct dark spots; second row of scales similarly colored but more
suffused with dusky pigment, blending into the darker duller color of
the dorsal surface.
A female of 720 millimeters snout-vent length, presumably about 20
months old, but not gravid, on June 13, 1962, was described as
follows: Juvenal pattern no longer clearly discernible but scattered
traces of it remain; dorsal color predominantly grayish olive, with
occasional small black spots in streaks scattered irregularly over
dorsal and lateral surfaces; at anterior end of body lateral scales
have bluish green edges but this shading becomes less noticeable
posteriorly; head mostly olive dorsally with marking obscure;
parietals have a large faint blotch; supralabials retain faint dark,
brownish markings on their upper parts; dark spot on median edge of
each prefrontal; supraoculars slightly darker than adjacent scutes;
chin mostly white, with yellowish suffusion at edges of scales;
ventral surface predominantly yellow, but fading to grayish white
posteriorly; remnants of juvenal ventral spots faintly discernible as
tan or whitish areas on yellow ventrals.
Munro (1950b:124) mentioned a blue racer of 749 millimeters total
length (hence probably having a snout-vent length of 600 millimeters,
or a little less), which retained faint juvenal markings when caught
on June 23, 1948, even though it was sexually mature, since it laid
eggs on the night of July 4, 1948. During several weeks of captivity
this snake's markings faded perceptibly.
In fully adult blue racers, those more than three years old, the
juvenal markings have become completely obliterated. In those from the
area of my study, the dorsal coloration is subject to much individual
variation, typically olive brown, but ranging from pale bluish gray to
dark brown, dark blue, or slaty. In most, the dorsal color is uniform,
but in some there are streaks and isolated scales of black. The dark
dorsal color extends down the sides onto the lateral corners of the
ventrals and the subcaudals. The chin is white but the remainder of
the ventral surface is ivory colored.
_Bodily Proportions_
The slender and streamlined bodily proportions of the racer are
subject to change through allometric growth. The head, and especially
the eyes, are relatively large in the hatchling, and become relatively
smaller as growth proceeds. The relative tail length seemingly
increases in the growing young and then decreases slightly in adults.
Snout-vent length and tail length were recorded in almost all the
racers examined, but other measurements were recorded in relatively
few. In many racers, especially the larger adults, tails had been
damaged and lacked their terminal parts. Often only the tip was
missing, but, of course, such individuals were not usable in the study
of proportions of the tail. Table 2 summarizes information concerning
relative tail length in 935 racers of both sexes and various sizes,
from northeastern Kansas. Nearly all measurements are from the live
snakes; a few are from recently killed individuals.
In hatchlings, the proportions of the tail are not noticeably
different in males and females, but data indicate that the snakes'
tails are approximately seven per cent longer in males than in
females; as growth proceeds, the tails become relatively longer in
proportion to the body, in both sexes. The ratio reaches its maximum
in young adults, having increased from approximately 28 per cent of
the snout-vent length in males and 26 per cent in females, to 31 per
cent in males and a little more than 28 per cent in females. In the
largest racers, of both sexes, these percentages are slightly reduced.
Tail-length is subject to a fairly wide range of individual variation,
which tends to obscure the trends determined by sex and size.
Table 2. Relative Tail Length in Male and Female Racers of Different
Size Groups
=============+============================+============================
| Males | Females
Snout-Vent +--------+-------------------+--------+-------------------
Length in | Number | Mean ratio of | Number | Mean ratio of
Millimeters | of | tail-length to | of | tail-length to
| racers | snout-vent length | racers | snout-vent length
-------------+--------+-------------------+--------+-------------------
150-200 | 7 | 27.3 ± .833 | 2 | 26.3
201-250 | 24 | 27.8 ± .490 | 23 | 25.9 ± .479
251-300 | 9 | 28.8 ± .634 | 4 | 26.6
301-350 | 20 | 29.8 ± .246 | 11 | 25.0 ± 1.060
351-400 | 8 | 28.8 ± .530 | 12 | 27.5 ± .404
401-450 | 6 | 27.8 ± .775 | 5 | 26.3 ± .357
451-500 | 12 | 29.7 ± .434 | 6 | 26.8 ± .858
501-550 | 45 | 30.5 ± .283 | 15 | 27.6 ± .284
551-600 | 76 | 31.0 ± .218 | 35 | 27.1 ± .254
601-650 | 45 | 29.6 ± .313 | 64 | 27.8 ± .163
651-700 | 50 | 30.5 ± .241 | 36 | 27.1 ± .350
701-750 | 72 | 30.5 ± .177 | 45 | 27.6 ± .373
751-800 | 45 | 30.3 ± .373 | 38 | 27.8 ± .325
801-850 | 48 | 29.7 ± .274 | 50 | 27.5 ± .205
851-900 | 18 | 29.1 ± .519 | 35 | 28.6 ± .422
901-950 | 5 | 29.8 ± .672 | 31 | 26.7 ± .252
951-1000 | 1 | 29.5 | 19 | 26.9 ± .390
1001-1050 | .... | ..... | 15 | 25.9 ± .413
1051-1100 | .... | ..... | 6 | 26.4 ± .725
1101-1150 | .... | ..... | 1 | 28.5
1151-1200 | .... | ..... | 1 | 25.0
-------------+--------+-------------------+--------+-------------------
In 88 racers caught in the summer of 1962 the following measurements
were recorded: Head length, from tip of snout to angle of jaw; maximum
head width; greatest diameter of eye; circumference of neck;
circumference at mid-body; circumference at posterior end of body;
and circumference of tail-base. Because the measurements were small,
and were made in the field on active, struggling snakes, a high degree
of precision could not be attained, and the range of error was several
per cent, with occasional relatively large errors. Nevertheless,
ontogenetic trends are clearly indicated. Most of the racers measured
were adults of small to medium size--in the range 500 to 799
millimeters, snout-vent length. Twelve females and seven males ranged
from 800 to 1035 millimeters, and seven young (all females) were less
than 500 millimeters. In measurements other than circumference of
tail-base, significant differences could not be found between males
and females of the same size group; therefore the sexes were combined
to obtain larger series.
Table 3. Bodily Proportions (Expressed as Ratio of Snout-vent Length)
in Racers of Different Sizes
==========================+===============+===============+==============
| Large | Medium | Small
Size Group |(more than 800 | (500 to 800 |(less than 500
| millimeters) | millimeters) | millimeters)
--------------------------+---------------+---------------+--------------
Length of head | 3.61 ± .036 | 3.82 ± .025 | 5.39
Width of head | 1.93 ± .049 | 2.02 ± .023 | 2.53
Diameter of eye | .56 ± .008 | .63 ± .009 | 1.00
Circumference of neck | 4.71 ± .082 | 5.05 ± .052 | 6.64
Circumference at mid-body | 7.11 ± .238 | 7.66 ± .082 | 8.58
Circumference at posterior| | |
end of body | 5.06 ± .113 | 5.03 ± .061 | 5.90
Circumference of tail | 4.23 ± .113[1]| 4.22 ± .075[1]| 4.66[1]
at base | 4.47 ± .171[2]| 4.66 ± .043[2]|
--------------------------+---------------+---------------+--------------
[1] Females.
[2] Males.
Table 3 shows that as compared with adults, the small young racers
have stouter, stubbier bodies, relatively large heads, and,
especially, large eyes. Allometric growth seems to continue throughout
life and the changed proportions of the adults are accentuated in the
largest and oldest individuals.
_Lepidosis_
Scalation that of typical colubrid (see Pl. 19); rostral large,
extending back onto dorsal surface of snout, bluntly pointed behind;
paired internasals considerably wider than long, convex anteriorly,
almost straight-edged posteriorly, each extends laterally to naris;
paired prefontals approximately twice size of internasals, and wider
than long, extending laterally on each side to level of nostril;
frontal convex anteriorly, concave on each side, bluntly pointed
behind, nearly twice as wide anteriorly as posteriorly; parietals
large; angle formed between them by frontal slightly more than 90
degrees; nostril large, situated between almost equal sized anterior
nasal and posterior nasal plates; loreal slightly smaller than nasals,
its anterior edge inclined forward superiorly; two rows of temporals
on each side; in upper row, first one narrow and elongate, second much
shortened, third intermediate in shape; in lower row all three
approximately alike in size and shape; two postoculars, the lower
larger; seven supralabials, first small and low, longer along upper
edge than along lower, second slightly longer than high, third higher
than long, contacting eye; fourth largest, contacting posterior part
of eye, and lower postocular; fifth nearly as large, pointed above;
sixth also large, pentagonal; seventh low and rectangular; on chin
first pair of infralabials separate mental from anterior genials;
second infralabial minute; third approximately twice its size; fourth
much smaller, rhomboidal, fifth also large, pentagonal; sixth smaller,
rhomboidal, bluntly pointed behind; seventh smaller, narrow behind;
eighth small and elongate; second pair of genials longer and narrower
than those of first pairs, separated from each other by smaller
scales; genials in approximately five rows, but somewhat irregular in
arrangement, mostly smaller and narrower than body scales; latter all
smooth, arranged in 17 rows for about two-thirds of body length, then,
by loss of third row on each side, reduced to 15; scales of neck
region rounded and relatively small, one-third to one-fourth size of
larger body scales; lowest scale row on each side largest with its
scales much wider and less symmetrical than others; most of body
scales of approximately hexagonal shape; on forebody they average
approximately twice as long as wide, but farther posteriorly on body,
width-length ratio gradually increases and some of scales, notably
those of lowest row, approximately as wide as long; regularity of
scale rows broken on sides just above vent by presence of many small
additional scales; on tail scale rows drop out posteriorly in rapid
succession, until on posterior third only four are present; ventrals
strongly convex posteriorly, with free posterior edges, nearly half
length of scales; anal plate divided, with diagonal suture; subcaudals
in double series, those of right and left sides alternating; several
minute subcaudal-like scales on each side of vent.
_Dentition_
In the racer the maxillary, palatine, pterygoid, and dentary bones
bear teeth (Fig. 1). The teeth are all much alike in size and shape,
small, sharp, and recurved, typically at an angle of approximately 50
degrees. The number of teeth present is variable. Because the teeth
are small and loosely attached to the jaw bones, and often are broken
off in the capture and ingestion of prey, each bone usually lacks part
of its complement of teeth. Even the sockets vary somewhat in number
between individuals, and between the left and right sides in some
snakes. Most of the skulls that I examined were not thoroughly
cleaned, and the adherent dried tissues made it difficult to obtain
accurate counts of the sockets. In ten skulls from Kansas and
Nebraska, most frequently occurring numbers of sockets for each of the
dentigerous bones were: maxillary, 15; palatine, 11; pterygoid, 18;
dentary, 18.
[Illustration: Fig. 1. Lateral view of right side of skull of adult
female blue racer, × 4. University of Kansas Museum of Natural History
no. 18305, from Greenwood County, Kansas.]
_Hemipenis_
Penial characters have proven to be useful in the classification of
snakes, providing bases for separating subfamilies, genera, and
species. In the racer even the subspecies have trenchant penial
characters by which they may be separated in some instances. The
hemipenis is roughly cylindrical, but widest at the base (Fig. 2). The
sulcus spermaticus is unbranched. Approximately the basal one-third of
the hemipenis has a smooth surface, broken only by the sulcus
spermaticus and by three greatly enlarged spines, which form
hooks--one anterior, one posterior, and one dorsal. The dorsal hook is
the largest of the three. Distal to the smooth part is a zone of small
spines, each recurved and mounted on a fleshy tubercle. The zone of
spines is poorly developed on the anterior side and is interrupted on
the posterior side in the vicinity of the sulcus spermaticus but is
best developed on the posterior side a short distance above and below
the sulcus spermaticus. The spines are arranged in several oblique
rows. Those of the proximal row are best developed, and there is rapid
diminution in the size of those situated farther distally.
Approximately the distal two fifths of the hemipenis forms a third
zone, lacking distinct spines, but having numerous deep longitudinal
grooves, alternating with lamellae which have fimbriated edges, and
which fuse with each other and divide to form a reticulated pattern.
[Illustration: Fig. 2. Lateral view of injected and everted left
hemipenis (slightly enlarged) of a blue racer from the Rockefeller
Tract, Jefferson County, Kansas, showing heavy spines at base of
organ, small spines of central zone and lamellae of terminal part.
This hemipenis is not fully engorged.]
Relationships
The large genus _Coluber_ is much in need of revision. Its many
species, perhaps more than a score in all, occur in North America from
southern Canada south to Guatemala, in eastern and southwestern Asia,
in southern Europe, and in North Africa. All are active,
slender-bodied snakes having smooth scales in few rows, and having
large eyes with well developed vision. The North American species fall
into two natural groups, the typical racers, and the whip snakes,
often assigned to a separate genus, _Masticophis_ (Ortenburger, 1928).
The whip snakes are more specialized than the typical racers in having
the eyes more enlarged, and the body form more slender and attenuate,
with number of scale rows more reduced. The racers of the Old World
are more diverse. Inger and Clark (1943) suggested a partitioning of
the genus _Coluber_ on the basis of the pattern by which scale rows
are reduced, from the maximum number on the forebody to the minimum
number at the posterior end of the body, supplemented by certain
characters of the hemipenis and of the cephalic scutellation. Besides
_Coluber_ and _Masticophis_ these authors recognized within the group
the genus _Platyceps_ with several species in southern Europe and
southwestern Asia; _Zamenis_ with several species in the same region
and in North Africa, and _Haemorrhois_, a monotypic genus of Spain,
North Africa and several Mediterranean islands. Although apparently
valid in principle, this arrangement has not been generally followed.
Exclusive of those species groups whose assignment to the genus
_Coluber_ are somewhat questionable, the remaining species in the
genus are: _C. constrictor_ occurring throughout most of the United
States and south along a narrow Atlantic coastal strip of Mexico to
Guatemala; _C. oaxacae_ of southern Mexico; and _C. spinalis_ of
northern China. _C. oaxacae_ is poorly known as only a few specimens
have been collected, but seemingly it is a near relative and
derivative of _C. constrictor_, especially of that species'
southernmost population. _C. spinalis_ is much more distinct, as might
be expected from its geographical remoteness. It is a slender, active
snake, of olive coloration dorsally with 17 scale rows and a bright
yellow, black-edged dorsal stripe and yellow ventral surface. It is
relatively small (up to 755 millimeters snout-vent length) and is
partial to riparian habitats but is also found in forests and in dry
and barren regions (Pope, 1935:224-226). It is known to feed upon
lizards.
Range
The common racer has been recorded in each of the 48 states of the
mainland of the United States, also in New Brunswick, Nova Scotia,
southern British Columbia, and southward through Mexico where it is
limited to a narrow strip of east coast lowlands but extends as far as
Guatemala. _C. c. constrictor_ occupies the northeastern states and
extends south into the Appalachian and Piedmont. _C. c. priapus_ with
its associated races _paludicola_, _helvigularis_, and _anthicus_ has
an Austroriparian distribution, occupying the Atlantic Coastal plain
and the Gulf Region, and extending north in the Mississippi Valley to
southern Illinois and Indiana. _C. c. paludicola_ is localized with
two disjunct populations--in the Everglades and on Cape Canaveral,
Florida. _C. c. helvigularis_ is even more restricted in range and is
known only from the Appalachicola region of the Florida Panhandle and
the adjacent corners of Alabama and Georgia. _C. c. anthicus_ occupies
much of central and western Louisiana and adjacent Texas. _C. c.
flaviventris_ occurs throughout the Great Plains, east in the "Prairie
Peninsula" through Michigan and northern Ohio and west to the Rocky
Mountains. _C. c. stejnegerianus_ occurs from Matagorda Bay in Texas
southward through eastern Mexico, with a seemingly isolated population
in the Sierra del Carmen region of northern Coahulia. _C. c. mormon_
occurs in the Pacific Coast states and Great Basin.
Actually, the range limits and the continuity of distribution within
the area outlined are still poorly known. The species has not been
recorded from the northern parts of Maine, Vermont, New Hampshire,
Michigan, Wisconsin, or Minnesota, nor from northeastern New York. It
is generally absent from southwestern desert areas. Records are
particularly scarce and scattered in the Rocky Mountain states,
suggesting that the distribution in this area may be discontinuous. In
a large area comprising all of New Mexico and Arizona, the western
half of Colorado, and the southern halves of Utah and Nevada, records
are so scarce as to indicate that the species is there represented by
only a few well isolated relict colonies. The type locality of
_mormon_ is "Valley of the Great Salt Lake," and there are numerous
records from the northern part of Utah east of Great Salt Lake
(Woodbury, 1931:75), but a record from Moab is the only one known to
me from the southern half of the state. The only records from western
Colorado are from three miles east of Fruita and two miles west of
Grand Junction, Mesa County (Maslin, 1959:56). Apparently the only
valid record from Arizona is that of Shannon (1950:59) from Eagar,
Apache County, in the east-central part. Shannon also recorded the
racer from Boulder Dam in extreme southern Nevada. Brattstrom
(1955:152) has recorded the species from the lower Pleistocene of
southeastern Arizona (Curtis Ranch), bearing out the idea that the
racer has partly withdrawn from a range formerly occupied in the
Southwest at a time when cooler and moister climate prevailed. Other
fossil occurrences are of late Pleistocene age--Vero Beach and
Seminole, Florida (Brattstrom, 1953a:245) and, doubtfully, Rancho
LaBrea, California (Brattstrom, 1953b:376). The range of _mormon_ has
been mapped (Wright and Wright, 1949:134) as extending east to
south-central Montana on the basis of one specimen allocated on the
basis of two characters. Otherwise the range of _mormon_ seems to be
entirely west of the Continental Divide, well separated from that of
_flaviventris_ by desert and mountain barriers. The conspecificity of
_mormon_ with the other subspecies needs to be more thoroughly
investigated, and geographic variation within _mormon_ also merits
study.
Geographic Variation
The common racer and the several species of whip snakes
(_Masticophis_) were revised by Ortenburger (1928). More recently with
much larger series of specimens, Auffenberg (1955) again revised the
classification of _C. constrictor_, but his study was concentrated in
Florida and neighboring southeastern states with relatively little
attention devoted to populations of the western and central United
States. As the species occurs throughout most of the United States and
south through the coastal lowlands of eastern Mexico to Guatemala, it
is found over a wide range of environmental conditions. Various
characters are subject to geographic variation, and some of them
follow clines that are maintained over extensive areas. Such
characters as the number of hemipenial spines, and the enlargement of
one or more basal spines into hooks, the shape of the premaxillary
bone, the number of maxillary teeth, the numbers of ventrals and
caudals, color of eye, number of dorsal saddle-marks and of ventral
spots in juveniles, and ratios of body proportions including tail
length to total length have been used to characterize the subspecies.
Also important is the shade of coloration of adults. The subspecies
_constrictor_, _priapus_ and _helvigularis_ that are characteristic of
forested habitats in the eastern United States are black dorsally and
have their ventral surfaces suffused to a large extent with dark or
dusky coloring. Farther westward the ground color becomes
progressively paler, greenish, grayish or light brown, and the ventral
surface is yellow (white on the throat and neck). The same tendency
appears in _C. c. paludicola_ of the Everglades. The populations of
arid climates in southern Texas and in the far western states are
relatively pale colored. The species thus conforms to Gloger's Rule in
changing from a pallid coloration in arid climates to a dark pattern
with eumelanins predominating in a humid climate.
Perhaps the most important character that is subject to geographic
variation in the racer, and certainly one of the most neglected, is
body size. With information now available it is not possible to
compare the sizes of different populations except in a general way.
The best sources of information concerning size in several subspecies
other than _flaviventris_, are the publications of Auffenberg (1949
and 1955). Comparison of these data with my own is not entirely
satisfactory because Auffenberg did not indicate clearly differences
in size between the sexes, nor indicate the boundary line between
young and adults. Also, his measurements are of overall length. For
the purpose of comparison I have subtracted 22.5 per cent, an
approximation of ratio of average tail length, from Auffenberg's
figures. He stated (1955:98) that the series of specimens on which
measurements were based were those "with a uniform coloration," that
is to say they had lost the juvenal pattern and were probably sexually
mature. Whether the same statement applied to the large series of
_stejnegerianus_ in the same author's earlier paper (1949:55) is
doubtful.
_C. c. constrictor_: 34 New York specimens averaged 806
millimeters (Auffenberg, 1955:96).
_C. c. flaviventris_: 100 Kansas specimens averaged 791
millimeters (males, 746; females, 836).
_C. c. priapus_: 171 Florida specimens averaged 713
millimeters (Auffenberg, 1955:96).
_C. c. stejnegerianus_: 291 Texas specimens averaged 664
millimeters (Auffenberg, 1949:54).
_C. c. mormon_: 94 West Coast specimens (Museum of Vertebrate
Zoology) averaged 563 millimeters (males 515, females 600).
_C. c. anthicus_: 35 northern Louisiana specimens estimated
to average 582 millimeters (Clark, 1949:249--the author did
not present individual measurements, but indicated the
numbers in several size groups in his sample).
The 100 _flaviventris_ in the above list were recorded in June, July
and August, a season when the young of the preceding year are still
small, and these young were not included. In a fall sample 63 males
averaged 729 millimeters and 65 females averaged 886 millimeters, but
with the nearly grown young (44 males and 40 females) included, the
averages were changed to 651 and 768 respectively. Maximum length
perhaps express differences between the subspecies as well as, or even
better than, the averages listed above. The following figures indicate
some of the maximum overall length measurements in inches that have
been published by various authors. These measurements pertain to
females unless otherwise indicated.
_C. c. constrictor_: 74-3/4, 74-1/4, 73, 65-1/2 (Auffenberg,
1955:96).
_C. c. flaviventris_: 71 (Pope, 1944:172), 72 (Conant,
1958:147).
_C. c. priapus_: 52-1/2 ([M]) (Auffenberg, 1955:98).
_C. c. stejnegerianus_: 37 (Auffenberg, 1949:54), 40 (Conant,
1958:148).
_C. c. mormon_: 51-1/2 (Museum of Vertebrate Zoology).
_C. c. anthicus_: 70 (Conant, 1958:149).
In my own study, the largest racers recorded from the Reservation and
Rockefeller Tract had the following overall lengths: 59, 57-1/4,
55-1/2, 58 [M] (projected from stub tail).
These sets of figures show that compared with the blue racer in
Kansas, with which my own study was concerned, the black racer of the
northeastern states reaches a larger size, while the racers of the
Southeast and especially those of the far West and of southern Texas,
are dwarfed. These size differences are almost certainly correlated
with behavioral and ecological differences among the snakes involved.
Adaptations to exploit certain types of prey and to utilize most
efficiently certain habitats and types of cover, have led to divergent
trends in different parts of the range.
Habitat
The racer dwells primarily in open situations, but as might be
expected from its extensive geographic range, bringing it under the
influence of diverse climates and habitats, its populations have
diverged somewhat in adaptation to different environmental conditions.
The eastern blacksnakes (subspecies _constrictor_ and _priapus_) seem
to prefer woodland and forest edge. In central Louisiana, _anthicus_
occurs chiefly in an open type of woodland. The subspecies
_stejnegerianus_ is found chiefly in brushland and thorn forest. The
western _mormon_ is found in varied habitats, including moist
streamside meadows, and chaparral. Published statements of
herpetologists, based upon studies in limited areas, are briefly
quoted below to show the trend of geographic change.
_C. c. constrictor_: This snake "occurs chiefly in fields" (Atkinson,
1901:148; Pennsylvania); "in more or less wooded regions and along
hillsides and among bushes" (Surface, 1906:167, in Pennsylvania);
"abundant, especially in wooded regions" (Hibbard, 1936:28, in
Kentucky); "dry and more or less open places" (Conant, 1938:52, in
Ohio); "old fields and areas about buildings" (King, 1939:572, in
Tennessee).
_C. c. priapus_: In "drier parts of the [Okefinokee] swamp ... seems
to prefer blueberries and saw palmettos" (Wright and Bishop, 1915:159
in Georgia); "common in grassy fields and in upland woods" (Allen,
1932:13, in Mississippi); "abundant along fence rows ... in dry
pine-oak forest and in bottomland forest" (Trowbridge, 1937:296, in
Oklahoma); "probably most abundant in open upland hammock or in old
fields; limestone flatwoods" (Carr, 1950:80, in Florida); Oak and
oak-hickory forest and small hill prairies in southern Illinois
(Rossman, 1960:219).
_C. c. paludicola_: In "all parts of the freshwater Everglades, in
cabbage palm hammocks, in salt marshes, and in mangrove swamps. On Key
Largo ... in mesophytic hammock" (Duellman and Schwartz, 1958:296, in
southern Florida).
_C. c. anthicus_: In "wooded areas in the vicinity of briar patches or
other brushy undergrowth" (Clark, 1949:249, in northern Louisiana);
"especially grassy uplands" (Fitch, 1949:88, in central Louisiana).
_C. c. stejnegerianus_: Of 291, 94 were in scattered brush, 92 in
sparse brush, 41 in lightly wooded areas, 26 in grassy areas, 24 in
heavy brush, eight in semi-arid places and six in heavily wooded
situations (Auffenberg, 1949:55, in southern Texas).
_C. c. mormon_: In "thin brush skirting open prairie land" (Lord,
1866:304, British Columbia); cottonwood-willow and water margin
habitats in prairie (Dice, 1916:310-312, in eastern Washington);
"grass; amid water cress; bank of small ditch near meadow; barley
field; sandy ground covered with rocks and driftwood; among sedges; in
sagebrush; swimming in irrigation ditch" (Grinnell, Dixon and
Linsdale, 1930:149, in northeastern California); low foothills, around
the fields, and in the timber and brush along the canyon bottoms
(Woodbury, 1931:75, in Utah); "open woods of Garry oak and poison oak,
on grassy slopes, in chaparral, and in grain or hay fields" (Fitch,
1936:644, in southwestern Oregon); "low hot canyons where it was found
to occupy areas having rather dry, rocky hills" (Ferguson, 1952:68, in
northeastern Oregon).
_C. c. flaviventris_: Pastures, meadows, and fields (Hurter, 1911:170,
in Missouri); "usually frequents dry open fields, although it is often
found in bushes or cut-over land which has grown up into thickets"
(Ortenburger, 1928:181); "pasture lands and on hill sides" (Peters,
1942:183, in Illinois); "along the levees in the salt marshes" (Liner,
1954:82, in southern Louisiana); "common in both prairie and woodland
habitat" (Smith, 1947:34, in east-central Illinois); Flood plain, sand
around sage-sumac brush, rocky slopes (Fouquette and Lindsay,
1955:411, in northwestern Texas).
Several observers have described the habitat in Kansas as follows:
"grassy valleys and thinly wooded hillsides" (Burt, 1927:5); "moist
and dry habitats, in wooded areas, and in prairies" (Smith, 1956:237);
Oak-walnut hillside forest, cultivated field, buckbrush-sumac, prairie
(Clarke, 1958:22).
Every part of the 590-acre Reservation is used to some extent by blue
racers living on this area. Home ranges of most individuals are so
large as to include a variety of habitats, both woodland and
grassland. The habitat preferences vary according to season. In autumn
some racers migrating to rock ledges to hibernate are found in mesic
forest, but at that time of year leaves have begun to fall and the
forest floor is less dark and humid than in summer. In spring also
racers not yet back on their summer ranges are often seen either along
the hilltop ledges, or moving downhill through woods toward bottomland
meadows. However, in summer, the finding of a racer in mesic woodland
is a rare event. Occasionally the snakes make trips across such blocks
of woodland hundreds of feet wide, but they do not linger in the
woodland. In decreasing order of preference the habitats used by
racers on my study area may be classified as follows:
1. Tall-grass prairie, (Plate 22) either original or regenerated,
dominated by native perennial grasses in stands three feet to seven
feet high, including big blue-stem (_Andropogon gerardi_), little
blue-stem (_A. scoparius_) Indian grass (_Sorghastrum nutans_), and
switchgrass (_Panicum virgatum_).
2. Pastureland, with introduced brome grass (_Bromus inermis_) and
associated weedy vegetation.
3. Brush, in ravines, at woodland edge, and in riparian thickets.
4. Weedy fields, dominated by such pioneer plants as ragweeds,
sunflowers, horseweed, milkweed, wild lettuce, aster and goldenrod.
5. Open type of woodland dominated by such trees as honey locust and
osage orange.
These habitat types are interspersed on the study area, and each racer
has a wide choice of habitats without travelling beyond the limits of
its own chosen area.
Grassland that has been closely grazed, mowed or burned does not
provide entirely adequate food or shelter, and under such conditions
clumps of brush or other dense vegetation may be of critical
importance. Throughout the racer's extensive range, fields of grain
and hay at times provide suitable habitat, and may support large
populations, but in spring, before the young cultivated plants have
made much growth, or later in the season, after they have been cut,
the racer may need to depend on adjacent areas of pasture, thicket, or
woodland edge and the availability of such refugia to a large extent
determines the numbers of racers on cultivated areas.
Temperature Relationships
In the locality of my study racers spend approximately half the year
in winter dormancy. Earliest spring records and latest fall records
for 13 years are shown in Table 4. The spring records in nearly all
instances pertain to snakes found in the open or beneath flat rocks
warmed by sunshine, usually at or near the rock ledges where
hibernation occurs. Juveniles are especially well represented in these
earliest spring records, and it seems that they tend to emerge a
little earlier, on the average, than the adults, either because they
have hibernated in more superficial and less well insulated situations
or because their lesser body mass permits more rapid warming to
activity than can occur in the adults. The latest fall records all
pertain to racers trapped along the rock outcrops, and none was a
young of the year.
Table 4. Earliest and Latest Recorded Annual Dates When Blue Racers
Were Active on the Reservation or Rockefeller Tract
==========+==========+=============++==========+==========+============
| Earliest | Latest || | Earliest | Latest
Year | spring | fall || Year | spring | fall
| record | record || | record | record
----------+----------+-------------++----------+----------+------------
1950 | April 16 | November 4 || 1957 | April 30 | November 2
1951 | April 19 | November 13 || 1958 | April 25 | November 20
1952 | April 23 | November 12 || 1959 | April 6 | November 10
1953 | April 8 | November 12 || 1960 | April 22 | November 6
1954 | April 20 | November 12 || 1961 | April 19 | November 1
1955 | April 15 | November 2 || 1962 | April 23 | October 27
1956 | May 11 | November 14 || | |
----------+----------+-------------++----------+----------+------------
Most of the population undoubtedly emerged somewhat later than the
average date of April 16 indicated by the records in Table 4, and
retired somewhat earlier than the average date of November 8. However,
a small percentage of the population probably emerged even earlier
each year than my records indicate, and retired into hibernation later
than my records indicate. In a typical year, temperatures in April and
early May are only occasionally above the level at which racers are
able to become active, but are below this threshold most of the time.
The same statement applies to an autumn period of late October and
November. Most racers are dormant in their hibernacula during these
transitional periods of spring and autumn, but some--those that have
emerged early in spring, or those that have not yet retired (in
fall)--retreat to temporary shelters and revert to a semi-torpid state
when temperatures fall below the critical level.
Fig. 3 shows the relative extent of activity along the hilltop
outcrops, as reflected by numbers of racers caught at different times
during the autumn. Data from 14 years are combined, and the large
composite sample indicates that in an average year there is relatively
little activity along the hilltop outcrops in early September, but
that activity rapidly increases to a peak in mid-October and then
tapers off rapidly, usually ending in mid-November, but occasionally
ending as early as late October or as late as late November.
The racers recorded in traps had, in many instances, been confined in
them for from one to three days before they were found. For any one
year records are not sufficiently numerous to show the trend as well
as Fig. 3, but Fig. 4 shows year-to-year differences; 1958 was a
fairly typical year, and also was the year in which the largest sample
was obtained; in 1949 the largest catches were made earlier than
usual, and the racers retired early into hibernation; in 1954 warm
weather persisted until unusually late in autumn, and racers remained
active beyond the time when they ordinarily would have been
hibernating; in 1955 and 1961 the most concentrated activity along the
outcrops, as reflected by day to day catches, came later than usual,
but unseasonably cold weather ended all activity abruptly, earlier
than usual.
[Illustration: Fig. 3. Records of blue racers trapped along hilltop
limestone outcrops in autumn, a composite sample of 14 years (1949
through 1962) from the Reservation and Rockefeller Tract, showing the
catch grouped in ten-day intervals, beginning with September 1 to 10
and ending with November 20 to 29. Averages of the maxima, means, and
minima of daily temperatures for each period are shown.]
The racer's annual cycle of activity is, of course, controlled
primarily by the weather, and is much delayed or accelerated in some
years. But certain stabilizing factors cause the racer's annual cycle
to be less variable than that of the weather. For example, in spring
when persistently cool weather delays emergence from hibernation
beyond the normal time, the increasing azimuth of the sun, and more
intense sunshine cause the soil to warm, despite low air temperature,
until emergence is finally triggered. Having once emerged, the racer
is able to control its bodily temperature to a large extent by basking
in sunshine to gain warmth, or by seeking shade or underground shelter
to escape overheating. By such behavioral thermoregulation extremes of
weather are neutralized, or at least buffered to some degree.
[Illustration: Fig. 4. Yearly variation in catch of blue racers along
hilltop outcrop in autumn on the Reservation and Rockefeller Tract,
grouped in same ten-day intervals indicated for Fig. 3.]
In the course of my study no racers were found in their actual
hibernacula. Insofar as known, these were always in deep crevices in
strata of limestone near hilltops, and were inaccessible except by
removal of the solid rock. The crevices where racers hibernate are
known to be several feet deep in some instances, extending well below
the frost line. Periodic temperature readings in two such crevices at
depths of 12 inches and 30 inches, taken in the winter of 1954 (Fitch,
1956:471) showed that temperatures during dormancy are usually well
within the range 0°C to 10°. Whether the racers congregate in
hibernating masses in regular "dens" on the Reservation has not been
definitely determined, but if so, most of the hibernating groups must
be small, because those trapped along the ledges are well scattered,
and, in fact, give the impression of being rather uniformly
distributed along them. However, ledges of northward exposure are not
used as hibernation sites, so far as known, and those of full
southward exposure are perhaps preferred, especially where the hilltop
has a southward projecting spur, and the exposed rock face is
extensive, with many cracks and fissures. I have been unable to detect
differences in types of hibernation sites preferred between the racer
and the copperhead, which is somewhat more numerous on the same area.
Several authors have contributed to knowledge of hibernation in the
racer. Boyer and Heinze in Missouri (1934:195) noted that blue racers
often were associated with copperheads in the vicinity of places
chosen for hibernation. Burt (1935:329) in Kansas found blue racers
emerging from dens among rocks on a prairie hillside, associating with
other snakes, _Diadophis punctatus_, _Elaphe guttata_, and _Pituophis
melanoleucus_. In the Chicago region, Pope (1944:173) reported scores
of blue racers aggregating in October on and around a sand dune with
oak woodland. In Ohio, Conant (1938:55) found three blue racers
hibernating together about three feet underground in a small hole. One
found at another locality had apparently hibernated in company with a
massasauga (_Sistrurus catenatus_). In Maryland Cohen (1939:137) saw
racers (_C. c. constrictor_) in the act of emerging from an old vole
burrow that was a communal hibernaculum, on April 6, 8, and 10. Air
temperatures at the time of emergence were 12.5° and 18.5° Centigrade.
In Illinois, Schroder (1950:1-2) found seven blue racers hibernating
in masses, intertwined with each other and with bull snakes at depths
of 36 inches and 42 inches in an abandoned mammal burrow in a sand
dune area in early February.
[Illustration: Fig. 5. Bodily temperatures of blue racers kept in a
large outdoor enclosure and checked from time to time when they were
active and the sun was shining, in June and July, 1962.]
In the course of routine field work I often carried a Schultheis
quick-reading thermometer, and from time to time I had opportunities
to take the body temperatures of blue racers newly captured by hand.
The trend of these records indicated the temperature range within
which the snakes normally limit their activity, and the preferred
temperature. In an earlier publication (Fitch, 1956:459-460) based on
a few more than half the number of records of temperature now
available, I discussed responses of the blue racer to temperature. The
newer data bear out the trends previously revealed; of 60 records, 39
are within the six-degree range from 29° to 35°, and records are most
concentrated in the one-degree range, 34° to 35°. Racers were found
active at air temperatures between 15.5° and 32.4°, with the greatest
concentration between 26° and 27°. Compared with most other kinds of
North American snakes, the racer is remarkably tolerant of heat, and
often is several degrees warmer than the level that those of other
genera will normally tolerate. Racers have been seen crawling in the
sunshine, or basking on days that were uncomfortably hot for humans.
For example, on August 28, a large female racer released from a trap
was followed and her behavior observed; after crawling some 50 feet
through the grass she climbed from a ditch bank onto sunflower stalks
and elm saplings, and came to rest among the stalks, in a spot
strategically situated for catching grasshoppers. More than half her
body was exposed to sunshine and air temperature was slightly above
34° Centigrade, yet the snake showed no sign of discomfort, and for
the several minutes that she was kept under observation, did not
attempt to withdraw into the shade.
[Illustration: Fig. 6. Bodily temperatures of blue racers captured by
hand in their natural surroundings. The preferred level is
approximately the same as indicated by Fig. 5 (between 29° and 36°
Centigrade), but some of the racers caught were not fully active and
had lower temperatures. Some bias results from the fact that those
having the lowest temperatures were the least active and hence were
most easily caught.]
[Illustration: Fig. 7. Air temperatures recorded at captures of the
racers whose records were used in Fig. 6. An active racer typically
maintains, by basking, a bodily temperature several degrees warmer
than the air.]
[Illustration: Fig. 8. Bodily temperatures of blue racers found in
live-traps at Harvey County Park. Opportunity to regulate temperature
by behavior was limited in these snakes in traps, which tended to
match ambient temperatures.]
At the Harvey County study area, bodily temperatures were recorded in
many of the racers that were caught in traps. These records are much
less significant than the records obtained from racers caught by hand
and promptly checked for bodily temperatures. The temperatures of the
trapped snakes may, to a large extent, reflect the temperatures of air
and soil at the time. However, despite their confinement, the trapped
racers probably were able to exercise some control over their
temperatures by shifting from shade to sunshine, or from the top of
the trap to its bottom, where they would be in contact with the
substrate. In most of the racers removed from traps, as in those
caught by hand, bodily temperatures were somewhat above air
temperatures, but the difference was less in the former group of
snakes. Figure 8 shows the bodily temperatures of these snakes removed
from traps. Occasionally racers died in the traps from overheating. On
July 2, 1960, each of two racers in traps had temperatures of 39.4°.
One of these was especially vicious and frantic in its attempts to
escape, but otherwise seemed unharmed. The second racer was dead,
seemingly having succumbed just before it was found. Probably
prolonged exposure to temperature in excess of 39° would always result
in death of the snake. Racers and other snakes that had become
overheated in the traps and were nearing exhaustion had a
characteristic limp feel when they were handled. In June, 1960, heat
tolerance of a halfgrown racer was compared with that of several other
snakes including a copperhead, garter snakes, and ringneck snakes.
Each snake in turn was enclosed in a plastic tube plugged with cotton
at one end, the snake having a quick-reading thermometer taped in
place for a rectal reading. The tube was then placed in sunshine. Over
periods of minutes the enclosed snake passed through a characteristic
cycle. Soon it would begin to register discomfort as its temperature
rose rapidly. Its struggles would become increasingly violent, then
would cease abruptly. The snake would suddenly collapse, its body
mostly limp, but knotted in slow contortions, its mouth gaping widely.
Within a few seconds all movements would cease, but in each instance
the seemingly dead snake was soon revived by holding it in cold
running water. The copperhead, garter snakes, and ring-necked snakes
all collapsed at temperatures near 41°. At this same temperature the
racer showed signs of acute discomfort, but did not collapse even
after many minutes of exposure. Probably more protracted exposure at
this level would have been fatal to the racer as well as to the other
kinds tested.
Home Range and Movements
Blue racers that were recorded on more than one occasion were rarely
caught again at the original location. For different individuals,
distances between capture points ranged from zero up to a little more
than three-fourths of a mile. The area of concentrated study was a
mile and a half in greatest diameter; there was scant opportunity for
capturing racers that moved greater distances. Even those that moved
as far as a mile would have passed beyond the boundaries of the study
area in most instances. Many of the marked racers that disappeared
from my records probably moved beyond the limits of the study area.
Nevertheless, in the great majority of instances, the distances
between successive capture points for the same individual were
relatively short, indicating that each racer tends to remain
permanently in a restricted area.
Most captures were made in the type of grassland or brush that
provides favorable habitat for the racer during the season of
activity, but many other captures were made in woodland along the
rock ledges where the snakes come to hibernate. Four different types
of movement may be recognized: 1) those in the rock ledge area where
hibernation occurs; 2) those between the area where the summer is
spent and the hibernation ledge--an actual small scale seasonal
migration which takes place in spring and autumn--3) those within a
home range, which are part of the day-to-day activities of the racer,
and, 4) wandering movements by which the racer shifts its activities,
perhaps permanently, from one area to another. In the records of any
one snake these different types of movements cannot always be sorted
with certainty. Each type will be discussed separately.
Relatively few movements along the ledges were recorded. It seems that
having migrated to a ledge, the racer promptly finds its hibernaculum
and retires for the winter. In spring there is equally prompt
scattering of the emerging racers, which no longer find the ledge
attractive. Most recorded movements along the ledges were short. Of 76
movements, nine exceeded 1000 feet, and only four others exceeded 500
feet. Most of the shorter movements were recorded within an autumn
season, but several were recorded after the lapse of one or more
seasons of activity. The longer movements were as follows: 1250 feet
after 8 seasons (male); 1300 feet after three seasons (female); 1600
feet after one season (female); 2000 feet after one season (female);
2280 feet after seven seasons (male); 2200 feet in same season
(female); 2410, 2600, and 3200 feet, each after one season (all
males). The trend of these records suggests that the tendency to
return year after year to the same hibernaculum is not strong; after
using one for a period of years, the racer may abandon the stretch of
ledge and, starting out in the opposite direction from its summer
range, find a new hibernaculum as much as half a mile from the old
one. Records of distances between capture points on the ledges for
individual racers are shown in Fig. 12.
A total of 124 movements between summer ranges and ledges were
recorded, and the distances averaged 1309 feet--approximately a
quarter mile. Some racers living in hilltop fields may have had home
ranges that included rock ledges, or at least were adjacent to them.
In such instances no seasonal migrations would have been necessary to
reach hibernacula in the autumn and summer ranges in the spring.
Several short movements--100 feet, 150 feet, and 200 feet--can be
explained on the basis that home ranges and hibernation ledges
overlapped or were near at hand, but most of the movements were
longer. The longest movement was 4020 feet, after a lapse of four
seasons. Twenty-four movements exceeding 2000 feet were recorded. For
these the intervals between captures averaged more than double the
time for the remaining movements, indicating that the longtime
permanent shifts were involved in many instances.
[Illustration: Fig. 9. Histogram of movements of blue racers between
hilltop rock outcrops used for hibernation, and summer habitat on the
Reservation and Rockefeller Tract. Movements of females tend to be
somewhat shorter than those of males.]
For all the racers living in bottomland, ranges were separated from
ledges by areas of wooded hillsides averaging approximately 700 feet
across. These relatively unfavorable areas had to be traversed in the
course of the semi-annual migrations. Even some of the racers that
lived in hilltop fields apparently crossed wooded slopes in order to
reach distant hibernation ledges, or else each reached the ledge by a
roundabout route although it could have found a ledge much nearer its
summer range. For the 124 ledge-to-field and field-to-ledge movements,
the median distance was 1030 feet. The sexes were almost equally
represented in this sample but the average distance for the 55
males--1425 feet--notably exceeded that for the 69 females--1220 feet.
These movements are shown in Fig. 9.
McCauley (1945:76) in Maryland described what seemed to be incipient
territoriality in a large male racer that remained several hours in a
small area, crawling about conspicuously with head raised, seemingly
on patrol. When an even larger male racer intruded, the first one
aggressively drove him away, but neither paid any attention to a king
snake that was also on the area. Other authors have noted the
attachment of a racer to a small familiar area. Conant (1938:53) wrote
that many of the racers he saw sought shelter in definite retreats.
One of these racers was seen resting on top of a brush pile four times
in a single afternoon, and each time it followed the same route to the
same inaccessible spot beneath the brush.
My own observations do not bear out the idea that racers maintain
regular territories, since several males may be present within a small
area, even in the breeding season. Hostile behavior between males has
not been observed by me under natural conditions, and in confinement
has been seen only in instances of self defense. Like the racer Conant
observed on a brush pile, individuals may linger in the vicinity of a
favored shelter or foraging area for periods of hours, but such
associations are ephemeral, and soon the snake moves on. In a
uniformly favorable habitat a racer may cruise about freely in tall
grass or brush. Individuals that I have attempted to follow, after
flushing them or releasing them from traps, often covered distances of
100 to 300 feet within periods of a few minutes before I lost them. In
such instances I maintained sufficient distance between myself and the
snake so that the latter was not actively escaping. Probably the snake
was not aware of pursuit in most instances, although I was able to
glimpse it through the stems of grass, weeds, or shrubs, or was
informed of its course by the swaying tops of grass and other
vegetation.
For many of the racers captured over periods of years it was possible
to plot "minimum home ranges" in the areas that they occupied. One
caught 12 times in five consecutive years will serve as a typical
example. There were seven locations involved; three captures were made
at one point and two captures at each of two others; the other five
locations were each represented by a single capture. One of the seven
locations was for a capture made at a rock ledge in October, and hence
can be eliminated from considerations of home range. The other six
locations are based upon captures made from late May to early August,
and they form a rhomboid pattern, with three locations in alignment on
one side and two others inside the quadrangular figure formed by the
five outlying points. Obviously such a group of records gives some
idea of the location and extent of the snake's activities but the
information is far from complete. As shown by Odum and Kuenzler
(1955), a much larger series of records, usually several dozen, with
eight or more marginal locations, is necessary to illustrate even an
approximation of the actual home range. Under the conditions of my
study such a series of records was unattainable. Few if any of the
racers recaptured had more complete series of records than the one
mentioned above.
For 20 racers the records were sufficiently numerous and well
distributed to permit plotting of minimum home ranges. One of these
ranges was hexagonal, nine were pentagonal, eight were rhomboidal and
three were triangles. In four instances the area encompassed was
broken by woodland, indicating that the home range comprised two or
three disjunct segments. In all instances the smaller segments were
triangular. The 20 minimum home ranges averaged 6.6 acres (3.2 to
12.8). The 15 ranges of males averaged 7.3 acres, whereas the five
ranges of females averaged only 4.5 acres, but the sample is too small
to be relied upon for differences in the sexes.
[Illustration: Fig. 10. Movements of blue racers within or between
areas of summer habitat on the Reservation and Rockefeller Tract. The
trends are much alike for males and females.]
In an earlier publication (Fitch, 1958:73) I discussed an alternative
method for determining size of home range in animals that move about
freely within a chosen area, not having their movements restricted by
attachment to a specific home base. Ordinarily any two records of the
animal within its home range will be separated _on the average_ by a
distance equal to half the diameter of the area. Assuming that home
ranges in general tend to have a circular shape, except as restricted
by limiting environmental factors, the area can be easily computed
from the average recorded movement--the home range radius. It is
necessary, of course, to have a sufficiently large number of records
of movements to obtain an average that is statistically reliable.
A major problem is that of recognizing movements that involve an
extension of the original range or a shift away from it to a new area.
A few exceptionally long movements were recorded. If these are
included in the computations of home range, they greatly increase the
average distance, probably introducing error. Also, the number of
exceptionally short movements was greater than might have been
expected if all locations of capture are at random to each other. In
some instances a racer newly released may have blundered into the same
trap again, or into the trap at the opposite end of its drift fence.
In other instances traps may have been so strategically situated with
respect to preferred travel routes that they caught the same snakes
repeatedly. In still other instances, the range of an individual might
have been mostly outside the study area, with only one end or corner
overlapping the trap sites.
A total of 471 records for consecutive captures in field areas is
available, 305 for males and 166 for females. In 20 instances
successive sites of capture were the same and movement was recorded as
zero. Of the 471 records, 207 involved a relatively long time span,
including at least one hibernation period; the remaining 264 were
based upon successive records within the same season of activity. The
trends were much the same in the records involving a longer time span
(up to four years) as in those records involving captures made in a
single season, but for the longer periods there were some
exceptionally long movements, and relatively few short movements of
less than 100 feet.
Records of male racers and those of females were used for separate
computations. For each series, the ten per cent of movements that were
longest and the ten per cent that were shortest were eliminated from
consideration in calculation of the average distance between points of
capture. For the remaining 244 records of males an average movement of
595 feet was calculated, and for 132 records of females an average
movement of 574 feet. These distances, if accepted as typical home
range radii, would represent home ranges of 26.3 acres for males and
23.8 for females. In an earlier discussion of spatial relationships in
the racer (Fitch, 1958:119), based upon relatively scanty data, I
estimated the home range to be approximately 23 acres in males. But
with only nine records for female racers I calculated the home range
to be 9.7 acres.
The disparate figures obtained from plotting minimum home range and
from calculating average home range radius are not irreconcilable,
since a minimum home range based on only four or five points would
ordinarily include only a fraction of the actual range. Distances up
to 1500 feet are included in the calculation of home range. It seems
that home ranges often have a diameter of this magnitude or a little
larger, although the estimated average diameter is 1140 feet. Home
ranges probably most often deviate from circular shape to form an
ellipse, with one diameter markedly exceeding the other. Woodland,
water, roads, buildings, or cultivated fields, or other areas that are
unfavorable or uninhabitable often form the boundary of a home range
and influence its shape.
Many of the longer movements constituted clear-cut shifts in range. In
one exceptional instance a large adult female captured in the
northeastern part of the Reservation on June 22, 1950, was released 21
days later at a point 3900 feet southwest of the place of capture. On
May 27, 1960 she was caught within 600 feet of the original location,
seemingly having made a homing movement. Among the nine racers
recorded to have made longest movements (exclusive of those movements
made to or from hibernacula) four were recorded also to have made
later long movements in the reverse direction, probably returning,
each to its original home range, although in every instance the return
movement was somewhat less than the original. A female of two-year-old
size when first captured on September 2, 1957, was recaptured 3100
feet southeast on May 10, 1958. On August 7, 1959, she was recaptured
again 2400 feet from the second location in the direction of the
original capture. Similarly, in a three-year-old female a shift of
2730 feet was recorded at the second capture after 21 months, and at
the third capture 14 months after the second, a return trip of 2360
feet had been made. A second-year female made a trip of 2640 feet
between May 17 and October 1, 1960; by May 1961 she had returned 2000
feet to the vicinity of her original capture. From one year to the
next an adult male shifted 2450 feet; after another year he had moved
back 1550 feet. Most of the longer movements recorded were those
between home ranges in fields and hibernacula along ledges, but in
this class of movements, distance was somewhat proportional to elapsed
time. For 59 such movements exceeding 2000 feet the average was 3.1
years, whereas for 114 field-to-ledge movements of less than 2000
feet, average elapsed time was 1.6 years. This trend suggests that
over periods of years a racer is likely to shift its range or its
hibernaculum or both.
[Illustration: Fig. 11. Map showing home ranges of five blue racers,
as indicated by numerous captures in successive summers, in small
valley where Reservation headquarters are located, and spatial
relations of their hibernacula, as represented by points of capture
along hilltop limestone outcrops. In spring and autumn, traveling to
and from hibernacula, the snakes migrate across wooded slopes. Each
"minimum home range" is enclosed in a dotted line, and a distinctive
symbol is used to show successive points of capture for each snake.]
[Illustration: Fig. 12. Map of 600-acre area of Reservation and
Rockefeller Tract, including parts where field study was most
concentrated, showing movements of the 20 blue racers recorded to have
shifted over the longest distances. The figure following the sex sign
of each individual indicates number of months elapsed between the
captures at the localities represented by the dots.]
Average elapsed time between captures was 7.7 months. In the 471
field-to-field movements recorded, 53--slightly more than eleven per
cent--exceeded 1500 feet and can reasonably be considered shifts of
home range. The average elapsed time between captures for this group
of snakes was 9.5 months. The evidence suggests that, even in an area
of favorable habitat, somewhat more than ten per cent of the racers in
a population annually shift their home ranges somewhat, but that many
stay in the same home range for periods of years or perhaps throughout
life.
Shifts in range were especially noticeable where availability of
suitable habitat underwent seasonal change. Along the north edge of
the Reservation, prairie adjoined cultivated fields where grain or hay
was grown. Until late May, the cultivated crops made little growth and
the fields were almost bare. They provided insufficient shelter for
the racers, which tended to keep to the prairie, where old grass of
the previous year's growth furnished them with ample cover. Later in
the season, crops, of oats, wheat, and alfalfa constituted suitable
cover for the racers, and many of them shifted their ranges to the
cultivated fields, but corn and milo crops were much less adequate for
their needs. After harvesting of crops, cover in the fields was again
inadequate for the racers' needs, and they tended to retreat to edge
situations, or to adjacent prairie.
Food Habits
_Methods of Obtaining Prey_
The racer hunts by stealth, but actively, obtaining its prey by keen
eyesight and swift movements. Wright and Bishop (1915:160) wrote that
because of its great speed it can catch anything that moves on the
ground. As a racer moves stealthily through dense vegetation, its
dull, uniform dorsal color blends well with the surface litter of dead
plant material. In prowling, the snake glides along rapidly and
alertly, in a jerky fashion, with frequent momentary pauses and
changes of direction. Because of its inconspicuousness, it is not
likely to be detected by the prey until it is close at hand. The snake
is ready to dash in pursuit of any small animal that flies, jumps or
runs to escape.
On August 27, 1955, my daughter observed a large racer hunting among
tall weeds at the edge of the pond on the Reservation. Several times
in the course of its movements, it flushed small frogs (_Rana
pipiens_) and each time the snake darted in unsuccessful pursuit of
the rapidly hopping frog. On several occasions I have been led to a
blue racer by the distressed croaking of a frog that the snake had
captured. In each instance, despite my cautious approach, the racer
saw me before I detected it, and then darted away, abandoning its
prey. On one occasion, while I was still a few yards from the racer,
and before the latter had detected me, the frog broke free and hopped
away rapidly through tall grass and weeds, and after several leaps,
hid, concealed by dense screening vegetation. The racer darted in
pursuit but could not find the frog. For several minutes the snake
persisted in an active search; with forebody elevated and head held
high, it would turn first in one direction and then in another, with
nervous, jerky movements, obviously keyed up to a high pitch of
excitement. Then it became aware of my presence, lowered its head, and
glided away rapidly, abandoning the search.
Although the racer depends to a large extent on sight to find its
prey, scent may play some part also, as indicated by the presence in
the food of young mammals taken from nests, some probably found
underground. Near Garnett, Kansas, on May 4, 1952, Richard B. Loomis
found a racer attacking a collared lizard (_Crotaphytus collaris_)
beneath a large flat rock. The lizard was retaliating by biting the
snake's neck. The posterior part of the snake protruded into the open,
and its thrashing had directed the attention of the observer to it.
Whether the racer first found the lizard under the rock, or followed
it there after flushing it in the open is unknown.
An encounter between a large blue racer and an adult Great Plains
skink (_Eumeces obsoletus_) on August 30, 1948, was described as
follows: "The skink, grasped by one flank, had twisted back and seized
the skin of the snake's neck in a bulldog grip, and they lay
interlocked, motionless except for their rapid panting, and occasional
straining of the skink to bite harder or of the snake to shift its
grip and work its jaws toward the skink's head. The racer broke the
skink's grip, and began to swallow it head first. When only the hind
legs and tail of the skink still protruded from the racer's mouth, I
lunged forward in an attempt to catch both reptiles. With a sudden
movement the snake disgorged the skink, which darted away into the
grass and escaped" (Fitch, 1955:78).
_Composition of Food_
Many authors have contributed to knowledge of the racer's food habits.
In most instances the records have been few or casual, but several
intensive studies have been made, notably by Surface (1906) in
Pennsylvania, Ortenburger (1928) for the species as a whole, Uhler,
Cottam and Clark (1939) in Virginia, Clark (1949) in Louisiana,
Auffenberg (1949) in southern Texas, Hamilton and Pollack (1956) in
Georgia, and Klimstra (1959) in southern Illinois. However, the
findings of different authors are not strictly comparable; some have
made general statements concerning the food habits but have mentioned
specific items only when these were considered unusual. Certain
authors have listed individual prey animals eaten; others have
indicated the percentages (in bulk or in frequency) that the different
kinds of prey comprised. Some writers have identified food animals
only in broad categories such as "insect," "beetle" or "snake" while
others have undertaken specific determinations for all the prey or for
certain taxonomic groupings that were subjects of special interest.
For the eastern black racer (_C. c. constrictor_) the following food
items have been recorded: 1 robin (_Turdus migratorius_, Storer,
1839:226); 1 copperhead (_Agkistrodon contortrix_, Verrill,
1869:158); 1 weasel (_Mustela_ sp.--presumably the diminutive
_M. rixosa_--Atkinson, 1901:148); 3 undetermined mammals, 1 rabbit,
1 undetermined mouse, 7 voles (2 _Microtus_ sp., 4 _M. pennsylvanicus_,
1 _Clethrionomys gapperi_), 1 undetermined bird, 2 robin eggs, 2
garter snakes (_Thamnophis sirtalis_), 1 water snake (_Natrix
sipedon_), 1 grass snake (_Opheodrys vernalis_), 1 green frog (_Rana
clamitans_), 1 wood frog (_R. sylvatica_), 1 grasshopper (_Melanoplus
femur-rubrum_) 2 camel crickets (_Ceuthophilus_ sp.), 5 moths
(cecropia, regal, imperial), 4 beetles, 1 currant worm, 1 ichneumonid
wasp (_Nematus ribesii_), 1 currant worm (Surface, 1906:170); 1 ribbon
snake (_Thamnophis sauritus_, Ditmars, 1907:282); 3 snakes (1
_Liopeltis vernalis_, 1 _Storeria occipitomaculata_, 1 undetermined),
6 white-footed mice (1 _Peromyscus leucopus_, 5 _P. nuttalli_), 1 vole
(_Microtus pennsylvanicus_), 16 crickets (9 _Gryllus pennsylvanicus_,
4 _G. assimilis_, 2 _Miogryllus verticalis_, 1 _Nemobius fasciatus_),
2 grasshoppers (_Dissosteira_ sp.), 1 lepidopteran, 3 elaterid beetles
(Ortenburger, 1928:200). Richmond and Goin (1938:310) recorded
finding the stomach of a black racer crammed with June beetles
(_Phyllophaga_). Conant (1938:53) recorded a black racer from Ohio
that had a smaller individual of its own species in its stomach. The
smaller snake contained a caterpillar. Uhler, Cottam and Clark
(1939:34) found food in 16 of 34 black racers from Virginia. Mammals,
including a shrew (_Blarina brevicauda_), a mole, a flying squirrel
(_Glaucomys volans_), a microtine, and a mouse (_Peromyscus_ sp.) made
up 26 per cent, 2 worm snakes (_Carphophis amoenus_), 2 ring-necked
snakes (_Diadophis punctatus_), and 1 water snake (_Natrix sipedon_)
made up 25.6 per cent, 5 birds including a warbler and a sparrow, made
up 17.75 per cent; 2 frogs (_Rana_ sp.) made up 9.38 per cent, 1 fence
lizard (_Sceloporus undulatus_) made up 6.25 per cent, and insects,
including cicadas (_Tibicen_ sp.) and larval lepidopterans, made up
15.09 per cent. In Indiana, Minton (1944:457) examined 11
food-containing stomachs; there were rodents in six, snakes in five, a
tree frog in one, and insects (cicadas, large grasshoppers) in four,
and another black racer was found swallowing a small box turtle
(_Terrapene carolina_). In Maryland, McCauley (1945:75) examined eight
digestive tracts and recorded a shrew (_Blarina brevicauda_) in one,
an unidentified mammal in one, 2 small cicadas in one, 2 small
chickens in one, a fence lizard (_Sceloporus undulatus_) in one, and
frogs and toads (including _Hyla crucifer_) in one; a ninth snake had
eaten a half grown rat. In Connecticut, Finneran (1948:124) observed a
large black racer eating a 21-inch garter snake (_Thamnophis
sirtalis_). Duellman (1951:338) recorded a black racer in Greene
County, Ohio, swallowing a large garter snake (_Thamnophis sirtalis_).
In Kentucky, Barbour (1950:104) recorded remains of an unidentified
snake in one stomach.
Many authors likewise have recorded food of the southern black racer
(_C. c. priapus_). In Georgia, Wright and Bishop (1915:160) recorded
finding 2 racerunners (_Cnemidophorus sexlineatus_), a skink
(_Lygosoma laterale_), 4 green tree frogs (_Hyla cinerea_) and 1 pine
woods tree frog (_H. femoralis_) in stomachs. They also stated that
the toad (_Bufo lentiginosus_ [= _terrestris_]) was the most important
article of food. Burt and Hoyle (1934:205) wrote that a racer from
Rogers County, Oklahoma, had eaten an adult male collared lizard
(_Crotaphytus collaris_). In Florida, Carr (1950:80) found one of
these black racers eating a leopard frog (_Rana pipiens_). Hamilton
and Pollack (1956:523) examined digestive tracts of 62 and found food
in 57, comprising the following percentages by volume: _Lygosoma
laterale_, 34.2; _Eumeces fasciatus_ and _E. egregius_, 11.3;
_Cnemidophorus sexlineatus_, 8.8; _Sceloporus undulatus_, 3.5;
undetermined lizard, 3.5; _Opheodrys aestivus_, 6.6; _Diadophis
punctatus_, 3.1; _Storeria dekayi_, 1.6; _Coluber constrictor_, 1.8;
_Heterodon platyrhinos_, 1.8; _Masticophis flagellum_, 1.8; _Rana_
sp., 5.3; _Hyla cinerea_, 1.8; _Hyla versicolor_, 1.8; _Peromyscus_,
1.8; undetermined rodent, 1.8; lepidopterous larva, 1.7.
In southern Illinois in an intergrading population of racers
intermediate between _C. c. priapus_ and _C. c. flaviventris_, Cagle
(1942:188) examined several stomachs and found 1 chipmunk (_Tamias
striatus_), 2 voles (_Microtus_ sp.), 2 mice (_Peromyscus_ sp.), 2
green snakes (_Opheodrys_ sp.), 1 water snake (_Natrix sipedon_) and
grasshoppers. From this same population Klimstra (1959:212) examined
137 digestive tracts of which 115 contained food as follows: 194
locustids, 118 gryllids, 17 undetermined beetles, 13 carabids, 6
scarabaeids, 10 lepidopterans, 9 hemipterans, 1 hymenopteran, 2
homopterans, 1 dipteran, 17 undetermined insects, 73 _Peromyscus_ sp.,
19 _Microtus ochrogaster_, 9 _M. pinetorum_, 12 _Sylvilagus
floridanus_, 3 _Scalopus aquaticus_, 3 _Rattus norvegicus_, 4 _Mus
musculus_, 2 _Tamias striatus_, 2 _Synaptomys cooperi_, 16 _Rana
pipiens_, 8 _Acris crepitans_, 2 _Rana clamitans_, 2 _R. palustris_, 1
_R. catesbeiana_, 4 _Hyla crucifer_, 3 _Pseudacris nigrita_, 4
_Lampropeltis calligaster_, 4 _Sceloporus undulatus_, 4 _Chrysemys
picta_, 1 _Heterodon platyrhinos_, 1 unidentified reptile, 4
_Sturnella magna_, 1 _Otocoris alpestris_, 4 unidentified birds.
Percentages by volume of the various categories in this sample were:
insects, 39.1; mammals, 32.9; amphibians, 10.8; reptiles, 8.3; birds,
6.3; miscellaneous, 2.6.
Food of the "buttermilk snake" (_C. c. anthicus_) is known only
through Clark's study (1949:249). In an unstated number of
examinations he found "mice" in 25, "rats" in five, lizards
(_Sceloporus undulatus_ and perhaps others) in eight, frogs (_Rana
pipiens_) in seven, and birds in three.
The food of _C. c. stejnegerianus_ is known only from the work of
Auffenberg (1949) but his sample was based on 206 racers that had
food, among the total of 291 recorded. Unfortunately, he did not
present actual numbers of the various prey animals, but divided the
food into seven categories and listed these as percentages. He did not
indicate whether the percentages represented volumes or numbers of
individual occurrences, and evidently there was some error in
computation since his combined percentages totalled 111. The
categories and their percentages were as follows: grasshoppers, 42.5;
crickets, 13.5; miscellaneous insects, .6; earless lizards
(_Holbrookia_ sp.), 40.1; scaly lizards (_Sceloporus_ sp.) 2.1; frogs
(_Rana_ sp.) 10.0; rodents, 2.2. Auffenberg divided his sample of
racers into five size classes, and showed that the smaller snakes fed
chiefly on insects whereas vertebrates were increasingly prominent in
the food of the larger snakes.
The food of _C. c. mormon_ is known chiefly through the work of
Ortenburger (1928:228) who cited instances of a skink (_Eumeces
skiltonianus_) and a young garter snake (_Thamnophis sirtalis_) being
eaten, and listed the following items from 24 stomachs that he
examined: 7 decticids, 8 acridids, 5 oedipines, 1 tryxaline, 6
_Melanoplus_ sp., 3 _M. mexicanus_, 2 _M. devastator_, 1 _M.
bivittatus_, 2 _Dissosteira carolina_, 1 _Chortophaga viridis_, 3
_Neduba carinata_, 3 _Trimerotropus_ sp., 7 _Hippiscus_ sp., 2
_Steiroxys_ sp., 3 _Canoula pellucida_, 2 _Stenopelmatus fuscus_, 2
_S. pictus_, 4 _Gryllus assimilis_, 4 _Ceuthophilus_ sp., 1
_Pristoceuthophilus pacificus_, 6 _Gammarotettix bilobatus_ and 2
cicada nymphs. Grinnell, Dixon and Linsdale (1930:149) found that one
of these racers had eaten a cricket. Fitch (1936:644) found another in
the act of swallowing an adult vole (_Microtus californicus_), and
recorded (1935:18) that two alligator lizards (_Gerrhonotus
multicarinatus_) were found in the stomach of still another. Woodbury
(1931:75) recorded that a racer from Utah had a sagebrush scaly lizard
(_Sceloporus graciosus_) in its stomach. Of the specimens examined in
the University of California Museum of Vertebrate Zoology, no. 17256
from the Mad River, Trinity County, California, had eaten an alligator
lizard (_Gerrhonotus coeruleus_), and no. 10120 from Yolla Bolly
Mountain in the same county had eaten a bird (unidentified) and a
Jerusalem cricket (_Stenopelmatus_ sp.).
Several authors have published specific information regarding the food
of _C. c. flaviventris_. Hurter (1911:171) caught a blue racer in the
act of swallowing a copperhead (_Agkistrodon contortrix_). Taylor
(1892:331) recorded finding garter snakes in several large racers.
Pope and Dickinson (1928:53) recorded instances of blue racers feeding
on racerunners (_Cnemidophorus sexlineatus_). Ortenburger (1928:181)
examined 22 stomachs and recorded: 1 large garter snake (_Thamnophis
sirtalis_), 1 vole (_Microtus pennsylvanicus_), 1 frog (_Rana_ sp.),
31 crickets (_Gryllus assimilis_), 4 decticines, 2 acridids,
grasshoppers (1 _Hippiscus_, 2 _Melanoplus_ sp., 1 _M. confusus_, 1
_M. differentialis_, 1 _Dissosteira carolina_, 1 _Sphargemon collare_,
1 _Trimerotropus_ sp., 1 _Orphulella_ sp., 1 _Chloealtis conspersa_, 1
_Chortophaga viridifasciata_, 1 _Omaseus_ sp., 1 _Pedocetes_ sp.), and
2 caterpillars (1 noctuid, 1 sphingid). Gloyd (1928:123) recorded a
hatchling glass lizard (_Ophisaurus attenuatus_) in the stomach of a
juvenal racer. Force (1930:31) found a racer eating eggs from the nest
of a cardinal (_Richmondena cardinalis_) and another racer eating eggs
of a red-wing (_Agelaius phoeniceus_). Gloyd (1932:403) recorded an
observation of a racer overpowering and swallowing a copperhead.
Anderson (1942:210) recorded remains of crickets and grasshoppers in
feces. Hudson (1942:55) recorded a racerunner (_Cnemidophorus
sexlineatus_) in the stomach of a juvenile and recorded an earless
lizard (_Holbrookia maculata_) 3 lizard eggs, and 14 grasshoppers
(_Melanoplus differentialis_ and others) in the stomach of another.
Marr (1944:484) found a harvest mouse (_Reithrodontomys montanus_) in
one. Breckenridge (1944:118) recorded stomach contents including a
garter snake (_Thamnophis sirtalis_), a frog (_Rana pipiens_), 3
crickets and 2 moths. Mossimann and Rabb (1952:27) recorded that a
racer disgorged several grasshoppers. Fouquette and Lindsay
(1955:411) recorded that a blue racer had eaten a harvest mouse
(_Reithrodontomys_ sp.). Carpenter (1958:114) recorded that one blue
racer had eaten a green snake (_Opheodrys aestivus_) and another had
eaten a grasshopper and a camel cricket.
Even though the sets of data cited above are not entirely comparable,
certain trends are evident. The black racers of the eastern states
(especially _C. c. constrictor_ of more northern regions) take a high
proportion of vertebrates in their prey. Among these vertebrates
snakes especially are well represented and the black snake would seem
to be of some importance as an ophiphagous predator. The birds and
mammals taken include some that are bulky (robin, cottontail, and even
a weasel--the most formidable prey eaten). Presumably the rabbits that
were eaten were young. In samples from the eastern United States
insects made up small to insignificant parts of the food; they were
lacking entirely or at least were not mentioned in the samples
examined by McCauley and Wright and Bishop. In the blue racer of the
central states, insects (mostly grasshoppers and crickets) are much
more prominent in the food and vertebrates correspondingly less
prominent. The vertebrates eaten are largely lizards, small snakes and
mice. _C. c. stejnegerianus_ is much like _flaviventris_ in the trend
of its feeding. _C. c. mormon_ is less known than these subspecies in
its feeding, but indications are that it takes a higher proportion of
orthopteran insects and smaller proportions of mammals and snakes than
do any of the other subspecies.
In my own field study a total of 1357 food records were accumulated,
one of the largest samples known for any kind of snake. Most of these
records were from the small area where my population study was carried
on, and studies of other kinds of animals, including those that were
the racer's prey, were simultaneously in progress. Because large
collections of reference materials were available, it was possible to
identify to species many of the prey items found, even though they
were incomplete and highly fragmented because most of them were
recovered from fecal material.
The prey is, of course, swallowed entire, and the recently swallowed
items squeezed from the stomachs provide the best material for the
study of food habits. However, relatively few racers had detectable
food items in their stomachs; digestion is rapid and often the snake
was in a trap for a day or more before it was found. Therefore the
greater number of records were obtained from scats. The residue in
scats consisted entirely of hard and indigestible parts such as the
chitin of insects' exoskeletons and the hair, feathers, scales, teeth
and occasional bone fragments of the vertebrate prey. The insects
eaten could usually be counted individually by sorting parts, such as
heads or hind legs. With mammals, birds and reptiles the hair,
feathers, or scales did not permit counting of individuals--each
occurrence was assumed to represent one individual but in some
instances two or more may have been present. Amphibians, lacking
indigestible dermal structures were in most instances not represented
at all in the scats, since their tissues were more or less completely
dissolved by the digestion of the snakes. Soft-bodied larvae of
insects and other invertebrates conceivably could be likewise
completely digested, but such occurrences must be rare, as most of the
invertebrates known to be eaten have the mouth parts, at least,
heavily chitinized.
Admittedly the factors discussed above would cause some bias in the
percentage composition of the food determined from scats, but I
believe that the amount of error introduced was slight, because,
judging from the records of items from stomachs, amphibians are not
eaten frequently, and even mammals are not eaten frequently enough so
that there is much chance of a snake taking two or more individuals at
the same meal, unless it is robbing a nest containing a litter of
young.
[Illustration: Fig. 13. Diagram showing percentage frequency of
occurrence of various categories of prey in a sample of 1008 food
items identified from scats and stomachs of blue racers from the
Reservation and Rockefeller Tract. Insects, especially, orthopterans,
made up the great majority of prey items taken.]
The largest sample, based on 1008 food items, was obtained from 479
scats collected from the Reservation and Rockefeller Tract over the
period 1949 through 1961. Items recorded were: 183 gryllid crickets
(144 _Gryllus assimilis_, 36 _Gryllus_ sp., 3 unspecified); 353
locustid grasshoppers (41 unspecified, 73 _Arphia simplex_, 67
_Melanoplus femur-rubrum_, 66 _M. bivittatus_, 39 _M. differentialis_,
17 _Melanoplus_ sp., 15 _Dissosteira carolina_, 8 _Chortophaga
viridifasciata_, 6 _Syrbula admirabilis_, 6 _Sphargemon equale_, 2
_Melanoplus scudderi_, 2 _Schistocerca obscura_, 1 _S. americana_);
94 camel crickets (_Ceuthophilus_ sp.), 93 katydids (36
_Neoconocephalus robustus_, 15 _Orchelimum vulgare_, 15 _O. nigripes_,
6 _Conocephalus_ sp., 4 _Orchelimum_ sp., 2 _Amblycorypha inasteca_,
1 _Neoconocephalus_ sp., 1 _Daihinia brevipes_); 7 cicadas (5 _Tibicen_
sp., 1 _T. pruinosa_, 1 _T. lyrica_); 45 unidentified insects; 17
beetles (including 1 _Phyllophaga_, 1 _Calosoma scrutator_, and 2
other carabids); 2 noctuid moths (_Mocis latipes_) and 1 caterpillar;
2 homopterans, 1 bee, 1 ant, 1 spider; 69 voles (59 _Microtus
ochrogaster_, 9 _Microtus_ sp., 1 _M. pinetorum_); 31 white-footed
mice (15 _Peromyscus leucopus_, 14 _Peromyscus_ sp., 1 _P.
maniculatus_); 36 miscellaneous small mammals (6 _Cryptotis parva_, 4
_Sigmodon hispidus_, 4 _Reithrodontomys megalotis_, 3 _Blarina
brevicauda_, 2 each of _Scalopus aquaticus_, _Sylvilagus floridanus_,
and 1 unspecified shrew); 50 snakes (16 _Coluber constrictor_, 15
_Diadophis punctatus_, 14 _Thamnophis sirtalis_, 4 _Elaphe obsoleta_,
1 _Natrix sipedon_); 7 lizards (5 _Eumeces fasciatus_, 1 _E._
_obsoletus_, 1 _Cnemidophorus sexlineatus_); 3 unspecified "reptiles";
5 birds (none identified to genus); 3 bird eggs, 1 narrow-mouthed toad
(_Gastrophryne olivacea_).
[Illustration: Fig. 14. Diagram showing estimated percentage by weight
of various categories of prey in a sample of 1351 items, including all
those represented in Fig. 13 and others from various parts of Kansas.
Since the vertebrate items are on the average much bulkier than the
insects eaten, vertebrates comprise most of the food, even though
insects are eaten in much larger numbers.]
[Illustration: Fig. 15. Diagram showing estimated percentages by
weight of various categories of prey in a sample of 69 food items
squeezed out of stomachs of the blue racers captured at Harvey
County Park. Most of the items were vertebrates, and lizards
(_Cnemidophorus_) were especially prominent in the food at this
locality. Samples of prey from scats (included in Figs. 13 and 14) and
from stomachs show somewhat different trends, and neither is entirely
representative of the actual feeding. Also, local differences in food
sources are important.]
Over the same period that the sample of scats was collected, a much
smaller food sample of 73 prey items was collected by squeezing
recently eaten food from the racers' stomachs, or by finding the
snakes actually swallowing their prey. These items from stomachs are
listed separately because they include relatively more vertebrates
than do the items from scats. A grasshopper or cricket eaten by a
large racer might have passed undetected, while a relatively large
item such as a vole or lizard would have produced a conspicuous bulge
in the snake that ate it, and would have excited the curiosity of the
investigator. A second difference is that the items from stomachs
included several frogs, whereas amphibians were absent from the much
larger sample from scats. A third difference is that the many insects
found in stomachs were all orthopterans with the exceptions of three
noctuid moths and the larva of a moth. Miscellaneous insects, such as
beetles, bees and ants recorded from scats were not found in stomachs.
Amphibians eaten are digested so completely that no recognizable parts
of them are to be found in scats, but remains of the insects
previously eaten by amphibians are to be seen in racers' scats. If not
recognized as secondary items, such remains might lead to erroneous
conclusions regarding the racer's food.
The items from stomachs were as follows: 21 grasshoppers (5 oedipines,
4 tryxalines, 5 _Melanoplus bivittatus_, 3 _M. differentialis_, 1 _M.
femur-rubrum_ and one each of _Chortophaga viridifasciata_,
_Dissosteira carolina_, and _Sphargemon equale_); 8 crickets
(_Gryllus_ sp.), 3 katydids, 3 camel crickets (_Ceuthophilus_ sp.), 3
noctuid moths, 1 larva of a moth; 10 voles (_Microtus ochrogaster_), 6
white-footed mice (5 _Peromyscus leucopus_ and 1 _P. maniculatus_), 4
harvest mice (_Reithrodontomys megalotis_); 1 shrew (_Cryptotis
parva_); 4 snakes (3 _Thamnophis sirtalis_, 1 _Storeria dekayi_); 4
lizards (2 _Eumeces obsoletus_, 1 _Cnemidophorus sexlineatus_, 1
_Ophisaurus attenuatus_); 4 frogs (_Rana pipiens_), 1 tree-frog (_Hyla
versicolor_).
Records from the Harvey County, Kansas study area include a series of
69 food items from 55 stomachs (of living snakes) and 210 food items
from 113 scats. There is a relatively high proportion of vertebrates,
including some frogs, in the stomachs, and with no frogs but more
miscellaneous insect material in the scats. But, for the sake of
brevity, the two categories of items are combined in the following
list: 55 grasshoppers (12 unspecified, 1 "locustid," 31 "oedipines," 7
"tryxalines," 5 "locustines," 2 _Melanoplus bivittatus_ and one each
of _M. femur-rubrum_, _M. scudderi_, _M. differentialis_, and _Arphia
simplex_); 48 crickets (31 _Gryllus assimilis_, 17 unspecified); 14
katydids (11 _Daihinia brevipes_, one each of rhadiphorine,
conocephaline and _Neoconocephalus_ sp.); 9 noctuid moths and 1 moth
larva; 26 miscellaneous insects (including 13 "beetles," 1 elaterid, 1
curculionid, 1 lygaeid bug, 1 ant, 1 wasp); 1 spider, 7 mice (5
_Peromyscus maniculatus_, 2 unspecified), 4 unidentified mammals, 1
vole (_Microtus ochrogaster_), 1 shrew (_Cryptotis parva_), 84 lizards
(77 _Cnemidophorus sexlineatus_, 6 _Sceloporus undulatus_, 1
unspecified), 6 snakes (4 "natricines," 1 _Thamnophis_ sp., 1
_Pituophis melanoleucus_), 1 "reptile," 1 "bird," 9 frogs (4
unspecified, 1 _Rana catesbeiana_, 4 _Rana pipiens_, 1 _Rana_ sp., 1
_Pseudacris triseriata_).
_Kinds of Prey_
Throughout the range of the racer small mammals make up an important
portion of the food, and the bulk of those eaten are voles (_Microtus_
sp.) and white-footed mice (_Peromyscus_ sp.). The voles being
diurnal, and having habitat preferences similar to those of the racer,
are especially subject to attack, but only large adult racers are
capable of swallowing a full grown vole. Probably most of the voles
eaten are immature. Of the white-footed mice, _P. maniculatus_
especially prefers a grassland habitat, and is usually found in
situations frequented by the racer. Being mainly nocturnal and
crepuscular, it is usually in hiding at times when the racer is
prowling, but may be flushed from its nest in a shallow burrow or
beneath a sheltering object, and overtaken by the snake. Other mammals
that are important in the food are harvest mice and other mice,
shrews, and young cottontails. The latter are small enough to be eaten
by racers only in the early stages of their life in the nest before
weaning. Rats (_Rattus_, _Sigmodon_), moles, sciurids, and weasels are
less frequent prey, ordinarily too large to be eaten by racers and
taken chiefly as defenseless juveniles.
Predation on birds is relatively uncommon, and in most instances it
involves the eggs or nestlings, or fledglings still slow and clumsy
and incapable of sustained flight, or, occasionally, injured adults.
Nests that are vulnerable are chiefly those of ground nesting species,
or of kinds that nest near the ground in grass or thickets. Many of
the birds recorded have not been identified to species, but those
identified have included a variety of small passerines and also
domestic chicks.
Lizards figure prominently in most of the food samples, but only a few
species, those that live on or near the ground in grassy places, have
been recorded. Most of the records pertain to scaly lizards
(_Sceloporus undulatus_ and _S. graciosus_), earless lizards (mainly
or entirely _Holbrookia maculata_), racerunners (_Cnemidophorus
sexlineatus_) and skinks (_Lygosoma laterale_ and _Eumeces_ sp.).
Snakes are important in the racer's food in most parts of the range,
but the large racers of the Northeast are those most inclined to
ophiphagous habits. The common garter snake (_Thamnophis sirtalis_) is
the species most commonly eaten. Probably this is a matter of
availability rather than preference, since the garter snake is one of
the commonest and most widely distributed of North American snakes,
occurring throughout most of the racer's range. The green snakes
(_Opheodrys_) also are represented frequently. The other snakes eaten
are mostly medium-sized to small colubrids, of a variety of kinds.
However, there are three records (from Connecticut, Missouri and
Kansas) of the racer preying on the venomous copperhead. There are
many records of the racer preying on smaller individuals of its own
species. In my own records racer remains appeared 18 times, equalling
in frequency those of the common garter snake and exceeding all other
kinds. In four of these instances the scale remains were relatively
few and the scales were relatively large, suggesting as an
alternative to actual predation that a racer may have eaten part of
its own sloughed skin, or that patches of shed skin may have adhered
to the scat after its deposition in the trap. However, in the
remaining 14 instances the remains of racer found in scats clearly
indicated cannibalism, since the scales found were small and numerous
and often were associated with bone. Cannibalism seems to occur
frequently enough to be a significant factor in the reduction of the
first year young. Liner (1949:230) described two instances of
cannibalism in a litter of blue racers hatched in captivity. In one
instance two young had seized the same lizard, and one having
swallowed the lizard, continued to engulf the other snake, although it
was of a size approximately equal to that of the first snake.
Nevertheless, swallowing was completed, with the snake eaten pressed
in a series of curves. A second instance of cannibalism occurred when
one young racer attempting to catch a lizard struck another racer by
mistake, then retained its hold and commenced swallowing. A similar
instance was observed in a brood that I kept in 1962 after hatching
had occurred in the laboratory.
Hatchling turtles of two kinds (_Chrysemys picta_, _Terrapene
carolina_) have been reported in the racer's food. Probably other
kinds are eaten also. However, the awkward shape and almost inflexible
shell of the prey on the one hand, and the slender form of the racer,
with limited distensibility of the gullet on the other, would limit
this type of predation to occasional instances involving an unusually
large racer and a small turtle.
There seem to be no records of the racer preying on salamanders. Many
kinds of frogs are eaten, chiefly ranids and hylids, and the leopard
frog (_Rana pipiens_) is the most frequent victim. Wright and Bishop
(1915:160) stated that the toad (_Bufo terrestris_) occupied first
place in the racer's food in the region of Okefinokee Swamp, Georgia,
but they mentioned no specific instances of this species being eaten.
Klimstra (_loc. cit._) found only four toads in his large sample of
digestive tracts from Illinois. Because of their virulent dermal
secretions, bufonid toads are avoided by many kinds of snakes and
predation on them by the racer probably is unusual.
Most authors who have written concerning the food habits of the racer
have mentioned insects as part of the diet. Statements in the
literature have often seemed to imply that the racer feeds on insects
in general, according to their availability. However, the large number
of records now available demonstrate that the racer is highly
selective in choice of its insect food, that soft-bodied orthopterans,
chiefly crickets, grasshoppers and katydids, are the usual insect
prey, with occasional predation on moths and their larvae. Eating of
other insects such as cicadas and June beetles, is a rarity, but on
occasion a racer may be tempted to sample such prey when it finds the
newly emerged imago before its exoskeleton has hardened. I am
convinced that such rarely occurring items as carabid beetles,
hemipterans, homopterans, diplopods and spiders are secondary prey
items, eaten by frogs that later were eaten by the snakes, in most
instances if not in all. It is noteworthy that several of the same
genera of grasshoppers and crickets are prominent in the food samples
collected in widely separated parts of the racer's range.
As might have been anticipated, different species of prey were not
utilized by the racers to the same extent throughout the snakes'
season of activity. Grasshoppers, for instance, fluctuated from a low
of 25.3 per cent (frequency) in the May sample to a high of 41.4 per
cent in the September sample. Availability of prey, rather than any
change of preference on the part of the racer, explains this trend.
Thus, the locust, _Arphia simplex_, which, unlike most local
grasshoppers, overwinters in the adult stage, is most prominent in the
food in May, represented by 15.7 per cent, but it decreases
progressively to a low of 1.8 per cent in September. The common
grasshoppers of the genus _Melanoplus_ show just the opposite trend,
increasing during the summer, from a low of 2.62 per cent in May (when
all are nymphs and most are too small to constitute a meal worthy of a
racer's attention) to a high of 31.5 per cent in September. Mammals
are best represented in the food in May, when they collectively
comprise nearly 30 per cent of the items taken, and they are
progressively less well represented as the summer advances. Both
_Microtus_ and _Peromyscus_ conform to this trend, but the relative
numbers of _Peromyscus_ rise again abruptly in October. The general
trend may be explained by the fact that in May most small mammal
populations have a high proportion of young of the year, and these
young are especially vulnerable to predation by the snakes. Also,
insects in general are less available in spring, and this may force
the racers to utilize vertebrates to a greater extent than at other
seasons. Actually, the seasonal changes in food sources are not
especially striking, and it seems that each important prey species is
utilized more or less throughout the season of the racer's activity.
Table 5. Distribution by Months of Various Categories of Prey Items
Recorded From Blue Racers From Kansas, Chiefly From the Reservation
and Rockefeller Tract
=======================+======+======+======+======+=======+======
| May | June | July | Aug. | Sept. | Oct.
-----------------------+------+------+------+------+-------+------
Cricket (233) | .17 | .37 | .28 | .01 | .05 | .12
_Ceuthophilus_ (94) | .01 | .19 | .30 | .14 | .13 | .23
Katydid (96) | .03 | .06 | .08 | .25 | .15 | .43
_Melanoplus_ (188) | .03 | .12 | .27 | .15 | .19 | .24
All grasshopper (388) | .15 | .17 | .21 | .16 | .12 | .19
_Microtus_ (79) | .45 | .32 | .13 | .02 | .07 | .01
_Peromyscus_ (39) | .41 | .18 | .08 | .08 | .05 | .20
All mammal (162) | .41 | .25 | .14 | .03 | .05 | .12
Lizard (70) | .07 | .46 | .29 | .15 | .01 | .02
Snake (61) | .37 | .18 | .08 | .13 | .09 | .15
_Arphia_ (72) | .50 | .25 | .12 | .04 | .03 | .06
-----------------------+------+------+------+------+-------+------
Table 6. Distribution of Various Common Prey Animals in a Sample of
625 Among Racers of Different Size Groups
====================+====================================================
| Snout-Vent Length (mm.) of Racers in Sample
Kinds of prey and +-----+-----+-----+-----+-----+-----+-----+-----+----
their percentage | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 |1000
frequencies in | to | to | to | to | to | to | to | to | to
in samples | 299 | 399 | 499 | 599 | 699 | 799 | 899 | 999 |1099
--------------------+-----+-----+-----+-----+-----+-----+-----+-----+----
gryllid cricket | .40 | .39 | .11 | .25 | .23 | .15 | .15 | .12 | .08
| | | | | | | | |
_Melanoplus_ | | .09 | .14 | .14 | .14 | .15 | .20 | .27 | .25
| | | | | | | | |
_Ceuthophilus_ | .20 | | .11 | .13 | .06 | .07 | .12 | .09 | .04
| | | | | | | | |
_Orchelimum_ | | | | .04 | .02 | .01 | .01 | .01 |
| | | | | | | | |
tettigoniid | | | .03 | .02 | .06 | .03 | .02 | .05 |
| | | | | | | | |
"other grasshopper" | | | | | | | | |
and miscellaneous | | | | | | | | |
orthopteran | | .30 | .25 | .10 | .09 | .03 | .12 | .07 | .09
| | | | | | | | |
_Arphia simplex_ | | | .03 | .02 | .05 | .08 | .08 | .04 | .09
| | | | | | | | |
miscellaneous insect| | .04 | .04 | .09 | .07 | .04 | .08 | .05 | .04
| | | | | | | | |
lizard | .20 | .09 | .18 | .09 | .07 | .11 | .01 | .01 |
| | | | | | | | |
snake | .20 | | .07 | .06 | .05 | .04 | .05 | .08 | .12
| | | | | | | | |
_Microtus_ | | | .04 | .02 | .08 | .13 | .09 | .12 | .25
| | | | | | | | |
_Peromyscus_ | | .09 | | .02 | .05 | .06 | .03 | .05 | .04
| | | | | | | | |
"other mammal" | | | | .01 | .04 | .10 | .03 | .03 |
| | | | | | | | |
bird | | | | | | | .01 | .01 |
+-----+-----+-----+-----+-----+-----+-----+-----+----
Total prey items| | | | | | | | |
for size group| 5 | 23 | 28 | 101 | 120 | 121 | 127 | 76 | 24
--------------------+-----+-----+-----+-----+-----+-----+-----+-----+----
The wide disparity in size between young and adult racers also results
in utilization of different food sources to some extent. In some kinds
of snakes adults and young draw their food from entirely different
sources, but in the racer there is broad overlap, as shown in Table 6.
The samples from the largest and smallest size groups of racers are
relatively small. Two important kinds of prey--voles and grasshoppers
of the genus _Melanoplus_--were not found at all in the smallest size
groups of snakes and comprised increasing percentages in the food of
the larger size groups. A large adult vole is too large to be
swallowed except by an unusually large racer, and a young vole old
enough to leave its nest is far too large for a hatchling racer.
Grasshoppers of the genus _Melanoplus_ are relatively large and
heavily armored, and so are relatively immune to attacks from the
smaller snakes. Small soft-bodied orthopterans including _Gryllus_,
_Ceuthophilus_ and _Orchelimum_, and also lizards and snakes, are best
represented in the food of the smaller racers. Other types of prey
showed no definite correlation with size of the racer taking them.
Reproduction
_Sexual Behavior_
Many observers have published accounts of the courtship and/or mating
of the racer, but all of these are, to some degree, incomplete.
Because of the widely different circumstances, and the different
viewpoints of the observers involved, the several accounts give much
different impressions of sexual behavior in this species. Either
singly or combined, the published accounts do not provide an adequate
description of the process.
My own observations, made both under natural conditions and in large
outdoor enclosures, are likewise somewhat incomplete, but indicate
that the whole sequence of courtship and mating is divisible into the
following well-defined stages: 1) the finding of a receptive female by
the male; 2) the persistent following of the female by the male, who
courts her by lying extended along her body and performing writhing
movements, with periodic interruptions during which he momentarily
leaves the female and courses rapidly through the grass around her; 3)
the acceptance of the male by the female, signalled by the raising of
her tail and the almost instantaneous intromission; 4) the dragging of
the passive male by the female while he is firmly attached to her
during the period of coitus; 5) separation of the pair and involution
of the male's hemipenis.
Even in the breeding season, racers that were confined in enclosures
usually were either indifferent to each other or responded with
reactions of fear or hostility. In moving they tended to follow the
edges, and often two moving in opposite directions would approach each
other; when this occurred, one snake might strike at the other with a
short jab that seemed to be mostly bluff, and then would dart away.
The males, being smaller, were usually the more wary.
Sexual behavior was noticed on only a few occasions. Several large
adult males were less wary than others and usually manifested
curiosity or interest toward other racers. My most complete
observations of sexual behavior were made on May 18, 1962, when a
newly caught adult male was added to an enclosure of 100-foot
circumference already containing several racers, two of which were
large adult females. Within half an hour the male was found courting
one of the females. She was lying in a loose coil, with the male
extended along her. At my approach the female darted away in alarm for
approximately three feet, and the male moved with her, so swiftly and
adroitly that he maintained contact and was in approximately his
original position with respect to the female when she stopped.
Spasmodic rippling movements passed down the body of the male as he
lay in contact with the female. These movements lasted several
seconds, increasing in intensity, alternating with longer periods of
little or no movement. As each period of vigorous writhing reached its
climax, the male's head jerked forward and backward several times in
seeming excitement. The female's behavior was mostly passive. She
seemed to be receptive, but from time to time, without any noticeable
warning, she darted away for several feet as she had when the pair was
first discovered. Each time the male darted forward with her,
maintaining contact while she moved. These swift movements of the
female seemed to be spontaneous, at least in most instances there was
no evident cause for alarm. The female's movements seemed to stimulate
the male's interest rather than to discourage him. In most instances
the female moved only four to five feet, then stopped abruptly or
turned back. She would stop in a loose resting coil, in thick grass,
with the male lying over her. Often she coiled in such a way that the
posterior end of her body was beneath her forebody, but this did not
seem to deter the male from moving the posterior end of his body into
position beside hers. After a sudden change in the female's position,
the rear of the male's body would perform groping movements along that
of the female until his cloacal region was approximately opposite
hers. The male sometimes had his chin pressed against the female's
back, especially when he was moving forward along her, but more often
his head was raised, and frequently was as much as 18 inches from the
female's head.
At intervals averaging approximately ten minutes, during a little more
than an hour of observation, the male would suddenly dart away from
the female, and with unusually rapid and animated movements, he would
move around her in an irregular and devious course, sometimes as far
as five feet away, but usually within 18 inches. Usually on each such
expedition several or many circuits were made; then the male would
return to the female and would glide rapidly along her until he
attained the mating position. A period of especially vigorous courting
movements would follow.
At 12:55 p. m. it was necessary for me to discontinue observations,
and I left the female confined in a cloth bag. Returning at 1:20 p. m.
I found that the male was not displaying interest in the female
confined in the bag, nor in the other female loose in the enclosure.
The first female was released from the bag, and was out of sight for
approximately four minutes. When relocated she was again attended by
the male, who was carrying on courtship even more vigorously than he
had before. At 1:35 p. m. the male achieved intromission. Although the
pair was under observation at the time intromission occurred, the
actual eversion of the hemipenis was not seen because the snakes were
partly concealed by dense vegetation. There was a sudden flurry of
movement, the male's head waving and his body thrashing. In an instant
these violent movements subsided, and after a few seconds the female
began to crawl forward slowly. The male had relaxed, and relinquished
his contact with the female anteriorly. As she moved away he was
dragged after her tail-first. He made slight backward wriggling
movements that perhaps aided in maintaining sexual contact. The
female's restlessness increased, and in eight minutes she dragged the
male in a circuitous course a distance estimated to be between 20 and
30 feet. At 1:40 p. m. the pair was ten feet from the point where
copulation had begun. The female showed increasing inclination to
climb, raising her head and forebody against the trunks of saplings,
and finally reaching up one to a branch 20 inches above the ground,
and climbing first along the branch and then farther up the main
trunk. As she progressed the male was lifted from the ground,
dangling limply suspended by his hemipenis and its base had become
exposed. At 1:43 p. m. separation occurred and the male dropped into
the grass. Semen dripped from the cloacae of both snakes. That from
the female was tinged with blood. The individuals involved in this
observation were kept in the enclosure subsequently but no further
sexual behavior was noted.
Contrary to the popular belief that these racers have permanent mates,
all available evidence indicates that they are promiscuous, and two or
more males may simultaneously court the same female in the brief
spring breeding season. On May 24, 1960, while I was walking in a
hilltop field of brome grass, a sudden movement attracted my attention
to three racers lying alongside each other. Only the posterior parts
of their bodies and their tails were visible. Two were males and were
performing the characteristic slow writhing movements against the body
of the female from either side. Although the heads were not in view,
the snakes may have been able to see me through the screening
vegetation; after I had watched for approximately 20 seconds, all
three suddenly took alarm, for no apparent cause, and scattered.
Further evidence of promiscuity is provided by the account of Ellicott
(1880:207) who wrote regarding the eastern subspecies: "I noticed a
ball of black snakes (_Bascanion constrictor_ L) rolling slowly down a
steep and stony hillside ... about two miles above Union Factory,
Baltimore County, Md. ... kept together by procreative impulses." It
was stated that this observation was made in early spring. "Snake
balls" have often been observed, and described in the literature;
usually the snakes involved were garter snakes (_Thamnophis_) or water
snakes (_Natrix_). Seemingly, typical aggregations consist of a single
adult female and several or many males attempting to mate with her.
There is a distinct possibility that the snakes involved in Ellicott's
observations were misidentified.
Sexual behavior of the racer is in most respects remarkably similar to
that of the common garter snake, _Thamnophis sirtalis_, well known
through the work of Blanchard and Blanchard (1942). In studying sexual
behavior of racers, several observers have failed to differentiate
between the different stages of the mating process, and have assumed
that copulation was occurring when actually only the precopulatory
behavior was observed. In an early description of courtship in this
racer in Kansas, Brons (1882:365) stated that the female "at times,
seems to toy with the male, indisposed to yield to his importunities,
though pressed with ardor. To avoid his suit, at times, she will dart
through grass, among stones, or enter a crevice. Should he be able to
reach his mate while within a hole, he is not slow in bringing her to
the surface, again to be repulsed. Upon an unbroken ground the sexual
union is less prolonged. Here she is unable to free herself from his
quick and effectively directed moves. In case she attempts to quit
him, a coil is thrown about her body, and his head laid flat upon her
neck, and replaced as promptly as dislodged, evidently in the endeavor
to propitiate her."
Another account probably based on courtship rather than copulation is
that of Wright and Wright (1957:135), who described the behavior of a
pair of _C. c. priapus_ on Billy Island, Okefinokee Swamp in southern
Georgia, on May 8, 1921, as follows: "They were stretched out, more or
less coiled ... the rear parts of the bodies from the vent were
entwined. The female, or smaller one seemed to have its tail around
that of the male. There were contortions or quiverings from time to
time.... May 8, 1921: Jackson Lee saw black snakes entwined, the male
seizing the female by the top of the neck."
Blanchard and Blanchard (_op. cit._) have described the dragging of
the male by the female during coitus in the garter snake, and the
temporarily inseparable bond formed between members of a pair by the
recurved spines of the engorged hemipenis, but it has not been
generally recognized that the process is much the same in other
colubrines. Cottam (1937:229) described and photographed mating in a
pair of _C. c. mormon_ in Utah. The copulating racers were shown in a
loose coil lying alongside each other with tails intertwined. However,
when disturbed by the observers, these racers made frantic efforts to
escape, crawling in a spiral course, while remaining attached and
intertwined, "with no evident attempt to separate" during
approximately a quarter hour of observation.
The racer is notorious for its aggressive behavior and occasional
alleged attacks on humans in the breeding season. The tendency has
doubtless been much exaggerated, especially in the verbal second- or
third-hand accounts based on the alleged observations of
eye-witnesses. Nevertheless, the supposition that large adults will
sometimes pursue or attack humans when disturbed is well
substantiated. In most of the instances known to me, it is the large
eastern subspecies, _C. c. constrictor_, involved in these incidents,
and seemingly the smaller racers of the Middle West, far West and
South are less inclined to behave aggressively. In May 1958 two pairs
of large racers were confined in a semicircular wire enclosure thirty
feet across and open on top, and with natural vegetation, at the
Reservation headquarters. Often in approaching the cage I saw two or
more racers in close association, but because of sheltering
vegetation, and the snakes' timidity observation was difficult. On May
19 a pair were lying partly extended in loose coils, but immediately
the female took alarm and darted away, breaking loose from the male;
his hemipenis was exposed, and underwent involution and retraction in
approximately 30 seconds. Unlike the female, the male on this occasion
did not attempt to escape, but turned to face me with a show of
aggressiveness. Probably copulation was in its final stages when the
disturbance occurred.
Circling of the female racer by the male from time to time in the
course of courtship has not been recognized by previous observers as a
part of the mating pattern, but Pope (1944:171) described somewhat
analogous behavior, probably modified by unnatural conditions of
captivity and the crowding of many racers in one cage. Pope, citing
earlier observations by Noble, wrote: "When sexually excited, the male
blacksnakes dash wildly about before paying court to individual
females. In captivity these dashes excite all specimens confined
together. A male, after picking out a mate, moves his chin lightly
along her back, while undulations run forward along his sides and he
extends his tongue now and then. Later he throws the part of his body
near his vent over the corresponding part of the female, the two tails
sometimes becoming loosely intertwined."
Recorded dates of mating for the species are all in spring, but
indicate a span of many weeks for the breeding season, and this spread
results in part from geographical differences. Published records are
as follows:
Subspecies _constrictor_
May 12, 1930, in Ohio (Conant, 1938:55)
Subspecies _priapus_
May 8, 1921, in Georgia (Wright and Wright, 1957:135)
May 9, 1921, in Georgia (Wright and Wright, 1957:135)
Subspecies _flaviventris_
May 3, 1931 (two pairs) in Missouri (Boyer and Heinze, 1934:195)
April 18, 1936, in Missouri (Anderson, 1942:210)
May 12, 1928, in Kansas (Gloyd, 1928:123)
Subspecies _mormon_
June 10, 1927, in Utah (Cottam, 1937:229)
July 7, 1938, in California (Cunningham, 1959:17)
In the course of my live-trapping, I occasionally found more than one
racer in a trap. As might be expected from the low yield per trap,
such double or multiple captures were relatively rare. Chance, and
unusually strategic placement of certain traps were doubtless
contributing factors. May and October, being the most productive
months for trapping, yielded a high proportion of these combined
captures. Some involved an adult and an immature snake, or two adults
of the same sex. Eliminating all these, there remain 44 heterosexual
captures of adults. These latter captures are significantly
concentrated in their seasonal distribution and indicate a spring
breeding season; 34 were in May, six were in June and four were in
October. Eight of the May records and one June record each involved a
trio of snakes--two males and a female in every instance. Distribution
of the spring records, grouped in five-day intervals, was as follows:
May 11 to May 15: 14 June 5 to June 9: 0
May 16 to May 20: 5 June 10 to June 14: 2
May 21 to May 25: 8 June 15 to June 19: 2
May 26 to May 30: 13 June 20 to June 24: 0
May 31 to June 4: 1 June 25 to June 30: 1
Approximately 87 per cent of the records fell in the twenty-day
interval, May 11 to 30, which is regarded as the main breeding season.
Presumably males continue to be at the peak of breeding condition and
continue to search for females after the latter have become
unreceptive, partly explaining the scattering of records through most
of June.
Several of the females found in traps with males in May had abundant
active sperm in their cloacae and oviducts and probably had been
inseminated within a few hours of the time they were checked. Others
lacked sperm, but the cramped quarters inside the traps may have
effectively prevented the consummation of courtship, especially when
two males were confined with the same female. None of the females
trapped with males in October was found to be inseminated, and it
seems doubtful whether copulation ever occurs at that time of year,
although males have motile sperm and seem to be in breeding condition
then.
_Cycle of the Male_
Cloacal smears indicate that males mature sexually and first produce
sperm in August and September when they are a little more than a year
old. Insofar as could be determined, there was no sexual activity at
this time of year, and actual breeding of the adolescent racers was
postponed until the following May. By this time at an average age of
20 months, the snakes had made further growth.
[Illustration: Fig. 16. Catches, in semi-monthly periods, of racers in
their summer habitats, at Harvey County Park (upper) and at
Reservation and Rockefeller Tract (lower). Intensive activity in
spring (the breeding season), tapering off rapidly as the season
advances, is well shown by the larger sample, but in the years of
trapping at Harvey County Park operations usually were not fully
underway until the latter part of May.]
Mr. Dwight R. Platt studied the changes in the male reproductive
organs during the annual cycle at Harvey County. In racers recently
emerged from hibernation he found the seminiferous tubules filled with
Sertoli syncytium, but containing few germ cells. Spermatogonia
proliferate in May and June. During the first half of July primary
spermatocytes are the dominant cells in the seminiferous tubules. By
early August spermatids are dominant and the first free spermatozoa
are present. In late October spermiogenesis is essentially complete
and the tubules are relatively empty before the snakes hibernate.
During the season of activity the seminiferous tubules increase to
approximately double their minimum diameter, reaching the maximum in
August. Cyclic changes in size and secretory activity of the ductus
deferens, ductus epididymis, and sexual segment of the renal tubules
occur, with maximum size and secretory activity coinciding with the
time of movement and storage of the spermatozoa. The latter are stored
in both ductus deferens and ductus epididymis. Despite the short
breeding season, a male racer has active sperm at all seasons.
_Eggs_
In accounts of the racer in the humid southeastern United States,
Brimley (1903:261), Wright and Bishop (1915:160) and Tinkle (1959:195)
mentioned the ease with which the eggs might be found and the
superficial situations in which they were sometimes deposited. Both
Wright and Bishop, and Tinkle made field studies in swamps, where
presumably the subsoil was saturated with moisture and too wet for the
eggs. Tinkle mentioned finding one clutch beneath a discarded
newspaper and another beneath a small, thin board. Surface (1906:167)
stated that in Pennsylvania the eggs were to be found in loose soil,
in sawdust piles, or in decaying wood of hollow logs or trees. Clark
(1949:249) stated that in northern Louisiana the eggs are laid in
soft, moist soil such as may be found beside decaying logs. Minton
(1944:457) found two clutches under flat stones on hillsides in
Indiana. In the more arid climates of the far western states the
species' habits are much different in this regard. Through many years
of familiarity with _C. c. mormon_, I have never seen its eggs.
Presumably nests in this part of the range are deep underground, most
often in old burrows of the pocket gopher (_Thomomys_), which are so
abundant that in many areas the soil is riddled with them. Burrows of
the ground squirrels (_Spermophilus_ sp.) and other small digging
mammals also provide potential insulated nest sites with the favorably
moderate temperatures and high humidities that the eggs of snakes
require.
On the morning of July 10, 1962, I was directed to the sites of two
clutches recently plowed up, 1-1/2 miles north of the Reservation (Pl.
21, Fig. 2). The eggs were in a fallow field having a stand of
sunflowers three to five feet high. The plow blades turned the soil at
a depth of approximately seven inches. In each instance only a few
eggs were visible. They were well scattered in the loose soil turned
up by the plow; 21 were found in one clutch and 10 in the other. All
the eggs were intact except two that had minute punctures from which
liquid oozed. Seemingly the eggs _in situ_ had been well above the
level of the blade--at depths of four to five inches. No nest
cavities were discernible where the eggs were found, but elsewhere in
the field tunnels of moles (_Scalopus aquaticus_) and prairie voles
(_Microtus ochrogaster_) were exposed by the plow. Presumably the eggs
had been in such tunnels, which had disappeared as the loose soil
crumbled. Another clutch was discovered in an adjoining field on July
16. The nine eggs were at depths ranging from 6-1/2 to nine inches,
and only the two topmost eggs had been turned up by the plow. All
three clutches were within a few feet of the edges of the fields.
On the Reservation and nearby areas I have seen remains of an
estimated 20 clutches that have been destroyed by predators. The
remains in every instance consisted of an excavation, and the strewn
torn and empty eggshells. Nests were at depths of four to eight inches
in old tunnels, which most often seemed to be those of moles but also
included some of the prairie vole, and perhaps some of the pine vole
(_Microtus pinetorum_). All these nests were in open sunny places in
prairie or pasture habitat.
Table 7. Numbers and Sizes of Eggs in Clutches of the Blue Racer From
Eastern Kansas
========+===============+=================+==============+==============
Number | | | | Snout-vent
of | Lengths | Widths | Weights | length of
Eggs | (mm.) | (mm.) | (grams) | female (mm.)
--------+---------------+-----------------+--------------+--------------
17 | 26.5(29-24) | 17.0(19.0-16.5) | 5.5(6.0-4.4) | 892
8 | 33.3(39-31) | 16.3(17.5-14.0) | 6.0(6.7-5.6) | 899
12 | 29.1(32-25.5) | 17.1(18.5-16.0) | 4.9(5.2-4.4) | 773
14 | 26.9(30-24) | 19.2(20-18) | 5.2(6.2-4.4) | 772
10 | 31.7(33-29) | 16.5(18-15) | 6.0(6.5-5.6) | 807
11 | 29.7(33-27) | 16.7(18-15) | 5.4(5.8-5.0) | 858
21 | 28.9(32-27) | 18.4(19.5-18) | 5.9(6.3-5.6) | 1038
13 | 30.7(34-28) | 19.3(20-18) | 6.8(7.5-6.1) | 907
18 | 29.0(30-26) | 17.9(19-16) | 4.9(5.5-4.3) | 911
12 | 30.3(34-28) | 17.8(19-15) | 5.2(6.1-3.8) | 843
14 | 30.9(36-29) | 19.4(21-18) | 6.8(7.6-6.2) | 846
--------+---------------+-----------------+--------------+--------------
Many observers have described the eggs of the racer, which are white,
elliptical, somewhat elongate, with tough, leathery, somewhat
flexible, shells, and a granular surface. Like other snake eggs, those
of the racer gradually absorb moisture during incubation. They become
more turgid and increase in weight and dimensions, especially in
breadth, and by the time of hatching are nearly twice their size at
laying. Between different clutches and even within the same clutch
there is notable variation in the size of the newly laid eggs. Munro
(1948:199) noted that in a small adult racer kept by him, the eggs
laid were larger but less numerous than those produced by a large
adult. Munro noted also that shape of eggs in the two clutches
differed; the smaller snake produced more elongate eggs of smaller
diameter. The idea that eggs laid by the smaller females are more
slender and elongate is not supported by my own data. For 11 clutches
of eggs examined soon after laying, dimensions, weights, and the
lengths of the females are shown in Table 7.
In a clutch of eggs beginning to hatch on September 3, 1958,
dimensions and weights were as follows: length 31.8 (36-30), diameter
22.0 (24-21), weight 9.7 (10.3-9.3).
Gravid females that were kept in captivity in anticipation of their
laying usually produced their clutches within a few days. The laying
dates of such individuals are shown in the following list. Those with
asterisks were from the Harvey County study area, others were from the
Reservation and Rockefeller Tract.
June 19, 1961 July 1, 1961 July 12, 1961
June 21, 1959 July 4-5, 1962* July 15, 1961*
June 23, 1961* July 6, 1955 July 18, 1961*
June 26, 1959 July 7, 1959* July 20, 1961
June 29-30, 1962* July 7, 1959* August 8, 1960*
A further indication of the period when laying occurs was provided by
the appearance of females gravid and progressively more swollen with
eggs, then their abrupt disappearance and replacement by thin and
wrinkled individuals that obviously were recently parturient. The
following records show the course of these events on the Reservation
in the years when summer trapping was done with sufficient
consistency. These dates provide a rough approximation of the time
when laying occurs locally. They indicate a laying season concentrated
in a period of approximately three weeks in this locality. Records
from published literature also indicate that laying occurs in late
June and early July at the latitude of Kansas, but somewhat earlier in
the southern United States.
Table 8. Dates When Parturient and Gravid Racers were Captured on
Reservation and Rockefeller Tract in Several Years, Indicating Time
of Oviposition
========================+=========+=========+=========+=========+========
Year | 1958 | 1959 | 1960 | 1961 | 1962
------------------------+---------+---------+---------+---------+--------
First parturient female | June 18 | June 17 | June 22 | June 20 | June 13
Last gravid female | July 8 | July 11 | July 5 | July 12 | July 16
------------------------+---------+---------+---------+---------+--------
Many authors have made statements regarding the size of the clutch in
the racer, on the basis of those found in the field, those laid after
capture, or those dissected from gravid females. Some of the
statements were based upon small but unspecified samples, and are far
from the mark. From records accumulated in the course of my own field
work, and a summarization of those in published accounts a substantial
sample is available showing the usual size of clutch in the area of my
study, and the trends of geographic variation in some parts of the
range.
_C. constrictor_ (all combined)
151 clutches averaged 10.61 (2 to 31) eggs.
_C. c. constrictor_ 14 clutches averaged 16.80 (7 to 31) eggs.
_C. c. priapus_ 11 clutches averaged 12.60 (7 to 21) eggs.
_C. c. mormon_ 43 clutches averaged 5.79 (2 to 13) eggs.
_C. c. flaviventris_ 82 clutches averaged 11.78 (5 to 26) eggs.
_C. c. stejnegerianus_, one clutch contained 10 eggs.
In the foregoing list the sample of _C. c. flaviventris_ may be
divided as follows:
Reservation and vicinity: 36 clutches averaged 11.65 (6 to 21) eggs.
Harvey County study area: 21 clutches averaged 12.0 (5 to 18) eggs.
Museum specimens from Kansas: five clutches averaged 9.2 (6 to 14)
eggs.
Published records (Kansas, Indiana, Iowa, Louisiana, Missouri,
Oklahoma, Texas): 20 clutches averaged 12.5 (5 to 22) eggs.
Table 9. Published Records Indicating Dates of Laying in Different
Populations of Coluber constrictor
===============+==================+============+=========================
Date | | |
of Laying | Subspecies | Area | Authority
---------------+------------------+------------+-------------------------
June 9, 1952 | _flaviventris_ | SE Texas | Guidry (1953:50)
July 1-2, 1920 | _flaviventris_ | Texas | Ortenburger (1928:183)
June 1, 1920 | _flaviventris_ | Texas | Ortenburger (1928:183)
June 9, 1926 | _flaviventris_ | Oklahoma | Force (1930:31)
June 24, 1926 | _flaviventris_ | Oklahoma | Force (1930:31)
July 19, 1928 | _flaviventris_ | Oklahoma | Force (1930:31)
July 16 | _flaviventris_ | Oklahoma | Carpenter (1958:114)
July 4-5, 1948 | _flaviventris_ | Kansas | Munro (1948:199)
July 4, 1948 | _flaviventris_ | Kansas | Munro (1948:199)
June 26, 1930 | _flaviventris_ | Ohio | Conant (1938:55)
July 3, 1961 | _mormon_ | NW Oregon | Van de Velde, Martan
| | | and Risley (1962:212)
June 7, 1957 | _priapus_ | S Illinois | Rossman (1960:219)
June 19, 1912 | _priapus_ | S Georgia | Wright and Bishop
| | | (1915:160)
July 10, 1940 | _priapus_ | S Illinois | Cagle (1942:187)
July 6 | _constrictor_ | New York | Ditmars (1907:284)
June 27-July | _constrictor_ | Virginia | Werler and McCallion
5, 1951 | | | (1951:251)
June 5, 1947 | _stejnegerianus_ | S Texas | Auffenberg (1949:54)
---------------+------------------+------------+-------------------------
Published records of clutches laid by racers, from which figures used
in the foregoing account were obtained, include the following:
_C. c. constrictor_: 22 (Barbour, 1950:104); 21, 13 (Brimley,
1903:261); 25 (Conant, 1938:55); 8 (Ditmars, 1907:284); 7,
12, 14, 16, 19, 20, 31 (McCauley, 1945:76); 14 (Wright and
Wright, 1957:136).
_C. c. flaviventris_: 7 (Anderson, 1942:210); 22 (Brumwell,
1951:205); 11 (Carpenter, 1958:114); 8, 9, 9 (Force,
1930:31); 10 (Guidry, 1953:50); 18 (Liner, 1949:230); 5, 8,
17 (Marr, 1944:484); 5, 14 (Munro, 1948:199); 13, 19
(Ortenburger, 1928:183); 6, 15 (Tinkle, 1959:195); 15, 19
(Wright and Wright, 1957:141).
_C. c. priapus_: 20, 21 (Cagle, 1942:187); 7 (Conant,
1938:55); 19 (Rossman, 1960:219); 5, 9, 11, 14 (Wright and
Bishop, 1915:160); 16 (Wright and Wright, 1957:147).
_C. c. mormon_: 13, 9, 8, 5, 5, 5, 4, 4 (Cunningham,
1959:17); 5, 6 (Stebbins, 1954:374); 6 (Van de Velde,
Martan and Risley, 1962:212); 3, 6 (Wright and Wright,
1957:144):
_C. c. stejnegerianus_: 10 (Auffenberg, 1949:54).
In general, the number of eggs in the clutch is proportional to the
size of the female producing them. The larger and bulkier females
produce more eggs. Geographic trends in number of eggs produced are
perhaps controlled by differences in size between different
populations; thus, the large eastern _constrictor_ produces nearly
three times as many eggs per clutch as does the small western
_mormon_, whereas the centrally located _flaviventris_ is somewhat
intermediate in size and in numbers of eggs produced.
In most reptiles growth in length and bulk continues after attainment
of sexual maturity. For many kinds including _Eumeces fasciatus_,
_Crotaphytus collaris_, _Cnemidophorus sexlineatus_, _Agkistrodon
contortrix_ (Fitch, 1954:60; 1956:236; 1958:36; 1960:174), and
_Sceloporus olivaceus_ (Blair, 1960:94), it has been shown that the
larger and older females in a population produce more offspring than
do the smaller and younger individuals. This situation applies in the
racer, as shown by the clutches of 52 females correlated with their
sizes and presumed ages (Fig. 17, Table 10). The two-year-olds
contribute a relatively small quota to the annual brood, partly
because their clutches are small, but more especially because many of
them fail to attain sexual maturity in time to breed. Many of the
female racers that are more than two years old also fail to produce an
annual clutch of eggs. The 24-day period May 28 to June 20 inclusive
is judged to comprise the period when eggs have generally enlarged
sufficiently to be detected in gravid females, but still have not been
laid in most instances. In this period, in 1960, 1961 and 1962, ratios
of gravid females to those not detectably gravid in several supposed
age groups arbitrarily established on the basis of size, were as
follows:
Two-year-olds 2 gravid, 13 apparently not gravid
Three-year-olds 5 gravid, 4 apparently not gravid
Four-year-olds 3 gravid, 2 apparently not gravid
Five-year-olds 4 gravid, 3 apparently not gravid
Six-year-olds (or older) 8 gravid, 2 apparently not gravid
[Illustration: Fig. 17. Graph showing number of eggs per clutch, and
correlation with supposed age (as deduced from length of body) in
female blue racers from the Reservation, Rockefeller Tract, and Harvey
County Park.]
From the appearance of these snakes it is reasonably certain that none
had already laid eggs when it was recorded, but there is some
possibility that a few individuals not noticeably gravid at the times
they were examined, produced eggs subsequently. However, these meager
data do seem to indicate that most of the two-year-old females and a
minority of older individuals fail to produce clutches in the annual
breeding season.
Table 10. Fecundity of Female Racers in Various Age-size Classes,
All From the Reservation and Rockefeller Tract
========================+===========+=====================+==============
Most Probable Age | Number of | Snout-vent length | Number
in Years of Females | females | of females; average | of eggs in
(as indicated by size) | in sample | and extremes | clutch
------------------------+-----------+---------------------+--------------
2 | 10 | 688 (589-748) | 9.2 (6-12)
3 | 19 | 789 (756-840) | 9.9 (5-14)
4 | 7 | 856 (850-861) | 10.8 (8-12)
5 | 6 | 907 (892-933) | 13.0 (8-17)
6 or more | 10 | 1005 (955-1088) | 15.7 (11-19)
------------------------+-----------+---------------------+--------------
Under unfavorable conditions eggs can be resorbed, but probably this
can occur only if initiated before ovulation. A racer in which six
small eggs were palped on June 28, 1960, was kept until July 23 but
did not oviposit. It no longer appeared gravid and the ova could not
be detected by palpation. Another female had 13 eggs on June 21, 1960,
but by July 23 when the snake was released the eggs had not been laid
and no longer could be detected. Both snakes refused to feed
throughout their confinement.
Like other reptilian eggs, those of the racer are dependent upon the
warmth of their surroundings for incubation. They are tolerant of a
wide range of environmental temperatures, but the higher the
temperature the more rapidly incubation proceeds. Under natural
conditions there may be much difference in hatching time in two
clutches laid at the same time and in the same locality. Site of the
nest--deep and well insulated, or shallow; in a well shaded situation
or one exposed to maximum amounts of sunshine--would largely control
rates of development. Clark (1949:249) writing of the subspecies
_anthicus_ in north-central Louisiana, stated: "eggs are laid about
the first of June.... young begin to make their appearance at about
... July 1." Even for the southern states these dates of laying and
hatching seem somewhat too early to reconcile with the records
published by other observers, and are in need of verification,
especially since they seem to be based upon vaguely remembered
observations rather than upon written records. At the other extreme
Surface (1906:167) wrote of _constrictor_ in Pennsylvania that
hatching may occur as late as October, and that there is evidence some
young may even remain in the egg over winter before hatching occurs.
Several incubation periods are on record for clutches laid and hatched
in captivity, as follows:
_C. c. mormon_, Oregon, 47 and 51 days (laid July 3, 1961,
hatched August 19 and 23; Van de Velde, Martan and Risley,
1962:212).
_C. c. stejnegerianus_, Texas, 73 days (laid June 5, 1947,
hatched August 17, Auffenberg, 1949:54).
_C. c. priapus_, S. Illinois, 58 and 59 days (laid July 10,
1940, hatched September 6 and 7, Cagle, 1942:187).
_C. c. flaviventris_, Kansas, 50 days (laid July 4 and 5,
hatched August 23 and 24; Munro, 1950:124).
_C. c. flaviventris_, Texas, 43 days (laid June 9, 1952,
hatched July 22; Guidry, 1953:50).
No incubation periods for eggs in natural nests have been recorded. In
the course of my study, eggs obtained from 12 captive females were
hatched in confinement, with an average incubation period of 51 days
(43 to 63) as follows:
Laid July 6, 1955, hatched August 20.
Laid July 3, 1958, hatched September 3 and 4.
Laid June 21, 1959, hatched August 17.
Laid June 26, 1959, hatched August 17.
Laid July 7, 1959, hatched August 23 to 25.*
Laid June 23, 1960, hatched August 20.*
Laid June 30, 1961, hatched August 30.
Laid July 15, 1961, hatched September 1 and 2.*
Laid July 18, 1961, hatched September 2 and 3.*
Laid July 4 and 5, 1962, hatched August 15 and 16.*
Laid June 29 and 30, 1962, hatched August 14 and 15.*
Laid July 6, 1962, hatched August 16 to 20.*
In the foregoing list those entries marked with asterisks were
obtained from the Harvey County study area; all others were from the
Reservation and Rockefeller Tract.
_Hatching_
Detailed observations on hatching were made on a clutch of eggs laid
on June 29 and 30, 1962, by a female caught in Harvey County. The
first egg in the clutch had already been laid in the trap when the
female was found at 11:30 a. m., June 29. Two of the eggs were
abnormal, with thin transparent shells, and were found to lack embryos
when they were opened on July 7. Later, two other eggs were attacked
by mold and the embryos died early in development. The clutch was kept
in a can of slightly damp soil. At 2:30 p. m. on August 13, when the
clutch was examined, egg no. 6 was found to have hatched. The young
snake had made a 21-millimeter slit in the shell. At 12:50 a. m. on
August 14, it was discovered that eggs 1, 4, 5 and 7 each had been
slit. No. 4 had two parallel slits separated by a two-millimeter strip
of shell, and the young racer could be seen inside. At 1:05 a. m.
this young snake had changed position and was lying upside down in the
egg, his snout protruding slightly through one of the slits. At 1:45
a. m. he was again right side up, still in the shell. At this time
each of the slit eggs showed the protruding snout of a young snake.
Occasionally the viscous liquid egg white would be blown into a large
bubble on the surface of the shell as the young snake exhaled. A third
slit, parallel to the others, had appeared in egg no. 4. A hatchling
emerged from egg no. 1 between 2:20 and 3:20 a. m., and another from
no. 7 between 7:00 and 9:00 a. m. The hatchling struck vigorously many
times, and vibrated his tail when he was disturbed. Egg no. 3 was
first slit between 7:00 and 9:00 a. m., and three more slits appeared
in it between 9:15 and 10:15 a. m. At 12:45 p. m. a hatchling was
found in the act of emerging from egg no. 4, and approximately the
anterior one-fourth of its body protruded. Disturbed by the movements
of the observer, the little snake drew back into its shell. This
hatchling began to emerge again at 12:50 and his hatching was
completed at 1:00 p. m. Between 5:40 and 6:20 p. m. a hatchling
emerged from egg no. 3 (for several hours this hatchling had been
lying on its back inside the egg, with only its snout protruding); two
slits appeared in egg no. 2 and three slits appeared in egg no. 8. At
6:50 p. m. the hatchling in the latter thrust his snout through the
slit in this eggshell. This hatchling was lying on its back at first
but by 10:50 it had shifted to a normal position. It emerged from the
shell between 2:35 and 2:50 a. m. Egg no. 2 was the last to hatch. At
7:05 p. m. the hatchling inside made two additional small slits in the
shell, and at 7:30 p. m. thrust its snout through one of them, while
lying on its back. At 1:45 a. m. it was right side up, but at 3:00 a.
m. had reverted to its previous position. At 4:40 a. m. it was again
right side up, and it emerged from the shell at 5:55 p. m.
On August 17, at 11:00 a. m., hatchlings no. 5 and no. 6 had lost
their egg teeth. All others still had their egg teeth then, but by
10:00 p. m. that of no. 8 was missing, and that of no. 4 was loose and
dropped out while the snake was being handled. On August 20 at 9:00 a.
m., hatchling no. 7 had lost its egg tooth; nos. 2 and 3 retained
theirs only in part, and no. 1 had its egg tooth intact. By noon on
August 22 no trace of an egg tooth remained on any of the hatchlings.
In the same group of hatchlings sign of impending molt was first
noticed on the morning of August 17, when no. 6 was noted to have its
eyes clouded and milky in appearance. By evening no. 1 had attained
the same stage and no. 7 was beginning to show it. On the morning of
August 20, shedding had begun in no. 6, while no. 2 and no. 8 had
milky eyes. The eyes had cleared in no. 1 and no. 7, and were still
clear in the remaining hatchlings. On August 22 shedding had been
completed by no. 1 and no. 8, and all others were in the process of
shedding.
Another clutch of 14 eggs from a recently captured female was found
freshly laid in a cage on July 6, 1962. Hatching of 13 occurred August
16 to 20, as shown in Table 11.
Table 11. Times of Hatching in a Clutch of Racer Eggs From Harvey
County Park
========+================================+=============================
| Time at which shell | Time that hatchling
Number | was slit by hatchling | emerged
of Egg +---------+----------------------+---------+-------------------
| Day | Hour | Day | Hour
--------+---------+----------------------+---------+-------------------
1 | Aug. 17 | 10:50 a. m. | Aug. 18 | 3:00 to 6:00 p. m.
2 | Aug. 17 | 12:15 to 12:50 p. m. | Aug. 18 | 3:25 to 4:25 p. m.
3 | Aug. 17 | 1:40 p. m. | Aug. 17 | 10:45 p. m.
4 | Aug. 18 | 3:00 to 6:00 p. m. | Aug. 19 | before 7:00 a. m.
5 | Aug. 16 | 10:45 a. m. | Aug. 17 | 6:30 to 7:55 a. m.
6 | Aug. 17 | 9:00 a. m. | Aug. 18 | 6:30 to 7:30 a. m.
7 | Aug. 17 | 4:15 p. m. | Aug. 20 | 1:00 to 7:00 a. m.
8 | Aug. 17 | 3:40 p. m. | Aug. 18 | 5:00 to 6:00 p. m.
9 | Aug. 17 | 7:30 p. m. | Aug. 18 | 6:30 to 7:30 a. m.
10 | Aug. 16 | 10:48 a. m. | Aug. 17 | 11:05 a. m.
12 | ? | no record | Aug. 18 | 6:00 to 6:30 a. m.
13 | Aug. 17 | 8:00 to 8:20 a. m. | Aug. 17 | 5:30 to 5:50 p. m.
--------+---------+----------------------+---------+-------------------
Growth
Hatching usually occurs in late August or early September, and the
disparity in size between hatchlings and adults is greater than in
some other kinds of snakes. In 76 young from ten clutches of eggs
incubated in the laboratory, averages and extremes for measurements
and weights were as follows: snout-vent length, 214.5 (186 to 244)
millimeters; tail, 59.3 (44 to 73) millimeters; weight, 4.16 (2.4 to
5.8) grams. In each brood the size tended to be fairly uniform, except
that there were usually one or more stunted individuals markedly
smaller than the others. However, there were striking differences in
size between the young of different broods. None of the young captured
was as small as the average hatchling from the clutches incubated in
captivity, but in the 14 years of my study only four young were
captured in August. The hatchlings are relatively secretive and
elusive, and the lush vegetation of late summer provides them with
abundant hiding places. Nevertheless it is remarkable that the
hatchlings are so seldom seem, when their probable abundance is taken
into account.
Probably all of those captured had already made some growth after
hatching. By early November or the last week of October, racers have
almost or quite completed their season of activity, and are at the
hilltop ledges, preparing to hibernate, if they have not already
retired into dormancy. For 25 young of the year captured in this
period at the end of the growing season, measurements and weights were
as follows: snout-to-vent, 327 (273 to 418) millimeters; tail 93 (72
to 114) millimeters; weight, 12.3 (7 to 19) grams. In the ten-week
period between hatching and hibernation these young had already passed
through their period of most rapid growth, having added, on the
average, more than 50 per cent to their original lengths, and almost
tripled in weight. In these young about to enter their first
hibernation, variation in size and weight is much greater than in the
hatchlings; some have fared much better than others, and there are
significant age differences. Within any one year the time of hatching
is spread over several weeks because of differences in the time of
laying, and differences in nest sites, with variation in heat
received, which promotes or delays the rate of incubation. Year to
year differences in the trend of weather increase the dispersion as
the incubation time is shortened in hot, dry summers and lengthened in
those that are relatively cool and moist.
Table 12. Growth of First-year Racers
=====+=================================+=================================
| Original record | Record(s) of recapture
+---------------+--------+--------+---------------+--------+--------
| | Snout- | | | Snout- |
Sex | | vent | | | vent |
| Date | length,| Weight,| Date | length,| Weight,
| | milli- | grams | | milli- | grams
| | meters | | | meters |
-----+---------------+--------+--------+---------------+--------+--------
[M] | Aug. 17, 1959 | 223 | 5.3 | Sept. 12, 1960| 503 | 42
[F] | Oct. 26, 1959 | 278 | 10 | Oct. 26, 1959 | 566 | 55
[F] | Nov. 2, 1959 | 340 | 18 | May 11, 1961 | 582 | 65
[F] | Nov. 10, 1959 | 348 | 13.7 | June 20, 1961 | 733 | 127
[F] | Oct. 19, 1952 | 361 | 15.3 | Oct. 9, 1953 | 620 | 68
[M] | May 9, 1953 | 368 | 17 | May 13, 1954 | 609 | 84
[F] | April 16, 1950| 328 | 142 | Oct. 10, 1950 | 603 | 78.2
[F] | May 17, 1956 | 358 | 15.2 | Oct. 6, 1956 | 575 | 52
[M] | Nov. 1, 1953 | 330 | 11 | May 21, 1955 | 674 | 92
-----+---------------+--------+--------+---------------+--------+--------
Though covering a wide size-range, the young of the year entering
hibernation are still a distinct size group, not yet overlapping that
of the next older group of young. Growth during the first year of life
is best shown by the individuals in Table 12, all of which were marked
either before their first hibernation or soon after emerging from it,
and were recaptured either the following autumn, or in spring soon
after emerging from a second hibernation.
These records indicate that the young racers at the time of their
second hibernation have grown to a snout-vent length of well over 500
millimeters, but less than 700 millimeters, and a weight of more than
40 grams but less than 100 grams. Other racers marked in the first few
weeks of life were recaptured after two or more seasons of growth, and
indicate the sizes that may be expected in young adults from two to
five years old, as shown in Table 13.
Table 13. Growth of Racers Marked at an Age of Less Than One Year and
Recaptured in Their Second, Third or Fourth Years
Column headings:
A: Snout-vent length in mm.
B: Weight in grams
C: Probable age in months
====+=================================+==================================
| Original record | Record(s) of recapture
Sex +---------------+-----+----+------+--------------+-----+-----+-------
| Date | A | B | C | Date | A | B | C
----+---------------+-----+----+------+--------------+-----+-----+-------
[M] | Nov. 12, 1952 | 342 |....| 2-1/2| May 20, 1955 | 702 | 110 | 33
[M] | Nov. 1, 1953 | 330 | 11 | 2 | Aug. 16, 1956| 780 | 162 | 35-1/2
[M] | Nov. 12, 1953 | 293 |....| 2-1/2| May 14, 1956 | 634 | 96 | 32-1/2
| | | | | Oct. 13, 1956| 689 | 110 | 37-1/2
[M] | April 15, 1955| 320 | 13 | 9-1/2| June 8, 1958 | 740 | 118 | 45
[M] | Oct. 2, 1955 | 348 | 18 | 1 | May 22, 1958 | 728 | 120 | 33
| | | | | May 21, 1960 | 795 | 130 | 57
[M] | June 25, 1959 | 378 | 10 | 10 | June 30, 1960| 590 | 60 | 22
| | | | | June 7, 1961 | 705 | 123 | 33
[M] | Nov. 1, 1953 | 330 | 11 | 2 | Aug. 25, 1957| 805 | 183 | 48
----+---------------+-----+----+------+--------------+-----+-----+-------
Unlike young of the year, racers in their second autumn were trapped
in large numbers. By this time all were large enough to be caught in
the traps of quarter-inch wire mesh, and they were the most abundant
size group. Many that were marked at this stage were recaptured after
intervals of months or years, showing the trend of growth. Some of
these snakes in their second autumn already had overtaken the more
retarded third-year individuals. The two age classes cannot be
separated with certainty. Selected records of individuals that were
almost certainly second-year young at the time they were marked are
presented in Table 14.
Table 14. Growth of Young Racers That Were Marked Near the Time of
Their Second Hibernation
Column headings:
A: Snout-vent length in mm.
B: Weight in grams
C: Probable age in months
====+==================================+====================================
| Original record | Record(s) of recapture
Sex +--------------+-----+-----+-------+---------------+-----+------+-------
| Date | A | B | C | Date | A | B | C
----+--------------+-----+-----+-------+---------------+-----+------+-------
[M] | Oct. 6, 1960 | 595 | 80 | 13 | July 23, 1961 | 650 | 70 | 23
[M] | Oct. 13, 1950| 525 | 52.6| 13-1/2| Oct. 2, 1951 | 675 | 105 | 25
[M] | Nov. 2, 1950 | 545 | 55.6| 14 | Oct. 24, 1951 | 670 | 100 | 26
[M] | Sept. 2, 1957| 522 | 57 | 12 | Oct. 14, 1958 | 690 | 103 | 25-1/2
[M] | Oct. 17, 1953| 558 | 47 | 13-1/2| May 10, 1955 | 718 | .... | 32
[M] | Nov. 14, 1956| 587 | 57 | 14-1/2| May 20, 1958 | 728 | 100 | 52-1/2
| | | | | June 17, 1959 | 880 | 219 | 64-1/2
[M] | Sept. 7, 1959| 533 | 45 | 12 | June 6, 1961 | 740 | 112 | 33
[M] | Oct. 17, 1959| 558 | 56 | 13-1/2| July 21, 1960 | 625 | 63 | 22-1/2
| | | | | June 7, 1961 | 670 | 95 | 33
[M] | Oct. 16, 1952| 577 | 62.0| 13-1/2| May 31, 1955 | 809 | 160 | 45
| | | | | May 11, 1956 | 855 | 144.3| 56-1/2
[M] | Oct. 11, 1950| 570 | 65.9| 13-1/2| July 11, 1956 | 820 | 193.6| 82-1/2
[M] | Oct. 14, 1953| 560 | 52 | 13-1/2| June 29, 1958 | 794 | 256 | 70
[M] | Oct. 6, 1950 | 563 | 55.8| 13 | Sept. 28, 1958| 907 | 243 | 109
[M] | Oct. 14, 1953| 523 | 44 | 13-1/2| May 19, 1959 | 818 | 190 | 80-1/2
| | | | | May 17, 1960 | 850 | 211 | 92-1/2
[M] | Oct. 13, 1953| 521 | 50.1| 13-1/2| May 13, 1958 | 814 | 166.4| 44-1/2
| | | | | June 3, 1959 | 826 | 165 | 47
[M] | Nov. 5, 1953 | 512 | 34 | 14 | May 22, 1958 | 847 | 135 | 69
[F] | Aug. 11, 1953| 534 | 39.2| 11-1/2| Sept. 18, 1954| 670 | 143 | 24-1/2
[F] | Oct. 14, 1949| 588 | 55.2| 13-1/2| Oct. 11, 1950 | 713 | 114.0| 25-1/2
[F] | Oct. 6, 1950 | 570 | 60.4| 13 | Oct. 11, 1951 | 783 | 174 | 25-1/2
[F] | Oct. 31, 1953| 582 | 58 | 14 | Oct. 5, 1954 | 860 | 195 | 25
[F] | Oct. 21, 1959| 588 | 63 | 13-1/2| May 7, 1961 | 730 | 120 | 32
[F] | May 14, 1960 | 506 | 34 | 20-1/2| Oct. 26, 1960 | 690 | 90 | 26
[M] | Oct. 22, 1960| 527 | 45 | 13-1/2| Oct. 7, 1961 | 620 | 74 | 25
[M] | May 3, 1960 | 530 | 48 | 20 | May 16, 1961 | 700 | 110 | 32-1/2
[M] | May 27, 1961 | 535 | 40 | 21 | Oct. 25, 1961 | 672 | 98 | 26
----+--------------+-----+-----+-------+---------------+-----+------+-------
From the records in Table 14 and many more like them, average and
extreme sizes for progressively older age groups were estimated. Even
racers that were already of adult size when they were marked were
tentatively identified with one or another age group, and their
records of subsequent growth were used. Most of the records show that
the females grow more rapidly than the males, and are, on the average,
larger at any given age.
Relatively few individual racers were recaptured after periods of
several years. Each of the eight listed in Table 15 is among those
that were captured in four or more different years, and their records
are significant in revealing the trend of growth after sexual maturity
has been attained. These snakes, one to three years old at the time
they were marked, show well the persistent but decreasing growth, and
the fluctuating weight that is characteristic of this and other
species.
[Illustration: Fig. 18. Graph from records of blue racers marked early
in life and recaptured, showing average and extreme snout-vent lengths
for males and females of various ages. Growth is especially rapid in
the first year, but continues, with gradual slowing, throughout life.
In hatchlings, the sexes are of approximately equal size, but females
grow to be markedly larger than males.]
Some of the largest racers recorded had already reached unusually
large size when they were first captured, so there was no opportunity
to determine their ages. Several others, originally captured as small-
or medium-sized adults, subsequently grew to a size approaching the
maximum, and thus provided a basis for estimating the ages of large
individuals. The records of nine such racers are listed in Table 16.
Table 15. Changes in Lengths and Weights in Eight Racers Recaptured
Repeatedly Over Periods of Years
=====================+=============+=============+========+==========
| Snout-vent | Tail length | Weight | Probable
Date of Capture | length in | length in | in | age in
| millimeters | millimeters | grams | months
---------------------+-------------+-------------+--------+----------
_No. 1, male_ | | | |
October 21, 1953 | 676 | 216 | 85 | 25-1/2
October 12, 1954 | 733 | 238 | 128 | 37-1/2
July 31, 1955 | 755 | 243 | 143 | 46
May 20, 1956 | 785 | 250 | 153 | 55-1/2
July 15, 1957 | 788 | 252 | 162 | 69-1/2
June 30, 1958 | 820 | 264 | 200 | 81
May 15, 1959 | 828 | 263 | 195 | 91-1/2
May 14, 1960 | 840 | 265 | 195 | 103-1/2
_No. 2, male_ | | | |
May 9, 1955 | 678 | 212 | 105 | 32
May 26, 1958 | 827 | 248 | 195 | 69
May 3, 1959 | 865 | 262 | 218 | 80
May 14, 1960 | 877 | 264 | 218 | 92-1/2
July 16, 1960 | 890 | 257 | 190 | 94-1/2
_No. 3, male_ | | | |
May 26, 1955 | 565 | 171 | 53 | 21
August 28, 1957 | 798 | 245 | 155 | 48
May 13, 1958 | 814 | 249 | 137 | 56-1/2
May 4, 1959 | 848 | 252 | 180 | 68
June 12, 1961 | 896 | 262 | 198 | 93-1/2
_No. 4, male_ | | | |
May 19, 1956 | 632 | 208 | 78 | 20-1/2
August 2, 1957 | 740 | 238 | 123 | 35
May 20, 1959 | 796 | 246 | 132 | 56-1/2
May 23, 1960 | 813 | 280 | 140 | 68-1/2
_No. 5, male_ | | | |
June 30, 1956 | 594 | 188 | 73 | 22
October 12, 1956 | 658 | 200 | 80 | 27-1/2
July 14, 1957 | 690 | 220 | 102 | 34-1/2
June 23, 1958 | 749 | 226 | 136 | 46
July 24, 1959 | 751 | 239 | 133 | 59
May 27, 1960 | 765 | 235 | 130 | 69
_No. 6, male_ | | | |
October 19, 1956 | 518 | 167 | 43 | 13-1/2
July 19, 1957 | 673 | 218 | 96 | 22-1/2
May 5, 1960 | 780 | 250 | 175 | 56
May 9, 1961 | 840 | 272 | 272 | 68
_No. 7, female_ | | | |
May 12, 1957 | 790 | 238 | 175 | 32-1/2
September 3, 1957 | 810 | 243 | 208 | 36
October 1, 1958 | 883 | 259 | 206 | 49
July 11, 1959 | 915 | 247[A] | 190 | 58-1/2
September 12, 1960 | 930 | 249[A] | 238 | 72-1/2
September 14, 1961 | 1012 | 268[A] | 332 | 84-1/2
_No. 8, female_ | | | |
June 23, 1955 | 601 | 175 | 67 | 22
August 3, 1958 | 920 | 255 | 300[B] | 60
July 23, 1959 | 955 | 281 | 211 | 71
May 18, 1960 | 962 | 262 | 260 | 81
---------------------+-------------+-------------+--------+----------
[A] Incomplete.
[B] With food.
[Illustration: Fig. 19. Graph from records of blue racers marked early
in life and recaptured, showing average and extreme weights in samples
of different ages. Early in life the females outstrip males in growth
and the size differential increases throughout life.]
A few adult racers recaptured, including different individuals of
small, medium, and large size, failed to make any measurable gain in
length over periods of months, or even over several years. Most often
the large individuals were those that failed to grow or made only
slight gains. Some of the snakes that failed to increase in length
suffered dramatic weight losses, perhaps as a result of injury,
disease, or parasitism. However, other individuals that failed to gain
appreciably in length did gain in weight. Doubtless both genetic and
environmental factors were involved. A few racers gave the impression
of being stunted by adversity. All records obtained of growth (or
failure to grow), throughout the period of my study were used in
compiling Table 17.
Table 16. Growth in Several Racers That Were Already Adult When
Originally Captured and That Subsequently Attained Unusually
Large Size
Column headings:
A: Snout-vent length in mm.
B: Weight in grams
C: Probable age in months
====+==================================+====================================
| Original record | Record(s) of recapture
Sex +--------------+-----+-----+-------+--------------+------+-----+--------
| Date | A | B | C | Date | A | B | C
----+--------------+-----+-----+-------+--------------+------+-----+--------
[M] | May 14, 1956 | 815 | 191 | 56-1/2| May 15, 1959 | 905 | 243 | 92-1/2
| | | | | May 16, 1961 | 945 | 287 | 104-1/2
[M] | May 22, 1958 | 825 | 251 | 68-1/2| June 25, 1959| 840 | 205 | 82
| | | | | May 27, 1960 | 880 | 210 | 93
| | | | | Oct. 14, 1961| 900 | 223 | 109-1/2
[M] | May 19, 1959 | 705 | 105 | 32-1/2| May 28, 1960 | 828 | ... | 45
| | | | | July 3, 1961 | 900 | 265 | 58-1/2
[F] | Nov. 6, 1954 | 823 | 190 | 38 | June 30, 1958| 1030 | 350 | 82
[F] | June 6, 1955 | 810 | 190 | 33 | May 21, 1959 | 1087 | 345 | 80-1/2
[F] | Aug. 29, 1957| 885 | 265 | 48 | Aug. 6, 1960 | 1041 | 235 | 83
[F] | May 1, 1958 | 633 | 84 | 20 | May 30, 1961 | 1088 | 320 | 57
[F] | July 20, 1958| 862 | 203 | 46-1/2| June 30, 1960| 1020 | 238 | 70
[F] | Oct. 18, 1956| 845 | 185 | 37-1/2| May 20, 1958 | 905 | 240 | 56-1/2
| | | | | Oct. 22, 1959| 1085 | 375 | 74
----+--------------+-----+-----+-------+--------------+------+-----+--------
Mortality Factors and Adaptations for Survival
_Defense, and Escape_
The behavior patterns that are associated with defense and escape in
snakes are widespread. The common racer is typical of the more
generalized snakes. Almost all elements of the racer's behavior are
found in snakes of other genera and perhaps, of other families. The
racer differs from these only in minor details of its behavior, in the
circumstances under which various behavioral traits are elicited, and
their relative importance. The common racer is one of the swiftest of
North American snakes, and it usually depends upon speed to avoid
enemies. Racers crossing roads may detect approaching automobiles at a
distance, and thereby may be stimulated to accelerate their movements
and so escape onto the shoulders rather than becoming traffic
casualties as many individuals of most other kinds of snakes do under
the same circumstances. The chances of such escape are of course much
better on dirt roads that are relatively narrow and have a rough
surface permitting efficient traction, than on wide smooth, paved
highways. The snakes are somewhat reluctant to venture onto open
expanses of pavement.
Table 17. Sizes of Racers of Different Age Groups in May and October
========+====================================================
| Males
+-------------------------------+--------------------
Age in | Snout-vent length in mm. | Weight in grams
Years +---------+----------+----------+---------+----------
| | Typical | Observed | | Observed
| Average | range | range | Average | range
--------+---------+----------+----------+---------+----------
1+ | 539 | 432-609 | | |
2- | 615 | 500-676 | 560-674 | 68.2 | 51-92
2+ | 668 | 610-700 | 620-710 | 107.4 | 63-134
3- | 706 | 677-730 | 648-755 | 102.1 | 65-129
3+ | 740 | 701-754 | 667-780 | 147.0 | 93-216
4- | 757 | 731-772 | 725-809 | 139 | 95-251
4+ | 785 | 755-793 | 720-850 | 167.4 | 128-225
5- | 805.5 | 773-810 | 743-855 | 152.4 | 110-198
5+ | 810 | 801-831 | 773-858 | 163.9 | 89-211
6- | 827 | 811-831 | 765-883 | 175.9 | 130-230
7- | 845 | 832-850 | 788-900 | 181.2 | 125-210
8- | 868 | 851-873 | 740-890 | 217.5 | 194-225
8+ | 870 | 861-884 | | |
--------+---------+----------+----------+---------+----------
| Females
+---------+----------+----------+---------+----------
1+ | 581 | | 415-658 | |
2- | 644 | 520-739 | 580-738 | 83.5 | 52-127
2+ | 743 | 685-804 | 670-826 | 135.2 | 73-200
3- | 810 | 740-829 | 730-880 | 149.4 | 98-219
3+ | 836 | 804-869 | 736-915 | 181.2 | 120-268
4- | 866 | 830-880 | 791-920 | 212.3 | 175-243
4+ | 883 | 870-914 | 810-952 | 191.2 | 143-300
5- | 914 | 880-929 | 833-1088 | 209.6 | 136-275
5+ | 932 | 915-954 | 883-990 | 250.4 | 195-336
6- | 965 | 930-961 | 892-1020 | 245.9 | 218-283
6+ | 970 | 955-980 | 885-1003 | 271 | 243-336
7- | 974 | 962-990 | 919-1050 | 251.3 | 150-330
7+ | 1000 | 980-1015 | 930-1085 | 295.6 | 235-375
--------+---------+----------+----------+---------+----------
A racer suddenly startled by close approach of a human usually flees
at high speed. The first part of its course, up to 20 feet or more, is
marked by a violent lateral thrashing of the body and tail, which may
help the snake to gain speed, but which seem chiefly designed to draw
attention of a potential attacker to the spot that the snake is
leaving. In any event, the mode of progression abruptly changes to a
swifter and much smoother travel, and the snake may seem to vanish
completely or as it glides rapidly away, its course may be marked by
the slowly waving tops of tall grass. The trend of travel away from
the site of disturbance is in an irregularly zig-zag course. The
method of crawling, with lateral undulations of the body, supported
against scattered pivot-points along the way, tends to prevent the
snake from moving more than a short distance in a straight line.
In checking traps along hilltop rock ledges in October, I have often
flushed racers that had come to the ledges searching for hibernation
dens. In such an instance the startled racer would usually dart away
down the steep slope at unusually high speed, and within a few seconds
might have covered 100 feet or more, progressing with a minimum of
lateral undulations, and seeming to flow or coast over the ground
surface with scarcely any effort. Although coursing downhill in this
manner provided an effective method of escape, racers startled at the
ledges or on other sloping ground sometimes followed a course parallel
to the ledge, or even turned uphill, with disastrous slowing. Often I
have accomplished capture by hand, by the strategy of running downhill
to get below the escaping snake, causing it to turn back up the slope,
there to be slowed to the extent that it could be overtaken.
A racer that has been flushed, and has disappeared after creating a
commotion by its violent thrashing, may, within a period of minutes,
return surreptitiously to the vicinity, gliding back slowly and
silently from the direction opposite that in which it departed. It may
climb into a tree or bush where, lying stretched on outer twigs and
concealed in dense foliage, it will sometimes permit close approach,
rather than reveal its presence by moving. If too much disturbed
however, such a snake will move away, higher, or to the opposite side
of the clump, with a slow and stealthy gliding motion which is likely
to escape detection. The sudden stops and abrupt changes in direction
make it difficult to follow the course of a climbing racer, even
though it is moving slowly. The tendency to climb to escape danger
seems to be especially strong in the western subspecies, _C. c.
mormon_. In my years of experience with the racers in the chaparral
belt of western Oregon and California, I found that one of the most
characteristic responses to danger was to climb into a bush or low
tree and seek concealment in the thick foliage. In most instances the
snake was from one to eight feet above the ground; usually it did not
attempt to climb high in a tree even when there was opportunity to do
so. The racer's prowess as a climber is limited. In thick brush where
its weight is supported by numerous stiff twigs simultaneously, it is
at home and can travel rapidly, but it cannot cling effectively to
rough bark of a vertical tree trunk as can the rat snakes (_Elaphe_
sp.) and others that are more specialized in their arboreal
adaptations. Chaparral-type shrubs such as _Ceanothus cuneatus_ and
_Arctostaphylos viscida_ were those in which western yellow-bellied
racers were seen climbing most frequently. Crab-apple (_Pyrus
ioensis_) and haw (_Crataegus_ sp.) were the shrubs most frequently
utilized by blue racers on the Reservation. Carr (1950:80) noted that
Florida racers were much less given to tree-climbing than were those
of more northern regions. _C. c. stejnegerianus_ of southern Texas is
reputed to have arboreal tendencies highly developed (Mulaik and
Mulaik, 1942:14).
The racers kept in an outdoor enclosure in the summer of 1962 spent
much of their time above the ground, climbing in several walnut
saplings. Usually in the warmer part of the day three or four of the
five racers in the pen were climbing. In the trees a racer usually lay
extended or in a loose coil among foliage in the outer twigs, at a
height of five to 12 feet. Such a snake might rest for hours in almost
the same position. Racers do not ordinarily enter the water
voluntarily, but they are swift and efficient swimmers when the need
arises. On one occasion a large female, seen near the edge of the pond
on the Reservation, and approached from the landward side, took to the
water without hesitation and swam strongly to the opposite shore more
than 100 feet away. Other observers have recorded similar incidents.
A racer that is suddenly startled at close range may make no attempt
to escape, but instead may coil and perform slow writhing movements,
with the head pressed to the ground and concealed beneath part of the
body. Musk, exuding from the anus is spread over the body surface as
the movements continue. Only a small percentage of the racers found
free in their natural habitats reacted in the manner described. In
each such instance, the circumstances were such that the racer was
prevented from making its usual rapid getaway, either because
temperature was unusually low for activity, or because the snake was
away from suitable cover. After removal from a live-trap, with
handling, and especially clipping of scales, racers were much more
likely to behave in this passively defensive manner, which seemingly
constitutes a second line of defense in snakes which have been
prevented from escaping--either cornered, captured, or injured by a
predator. The musk is creamlike in color and consistency, and is
secreted from sausage-shaped glands in the base of the tail. Its odor
is rather disagreeable, but less so than that of musks of various
other genera. Also, it is less penetrating and lasting than many other
musks. In handling the racers removed from traps I attempted to avoid
being smeared with the musk by grasping the snake by the tail and neck
and keeping its body stretched out. While the snake was being
examined, and measured a droplet of musk would form at the anal
orifice and would begin to flow down the snake's body. To avoid
contact with the musk I would wipe away the droplet with a paper towel
or leaf, but the musk droplet might be replaced several times within
the few minutes that the snake was restrained.
A racer that is confronted with an object arousing its suspicion or
indicating possible danger, may move away slowly with a characteristic
"threat display." The forebody and neck are held rigid, well off the
ground, and slightly arched, with the neck flattened in a vertical
plane--causing this part of the snake to appear from lateral view
larger than it actually is. The tongue is protruded frequently and
waved slowly. A racer that has been disturbed and is trying to gain
shelter in a direction that brings it closer to the danger usually
will adopt this tense attitude, but a single threatening movement will
cause it to abandon its circumspect pose, and panic in an attempt to
reach the nearest shelter in the shortest possible time.
A common response to an alarm is to vibrate the tail. The tail being
long and slender is vibrated much less rapidly than the short,
muscular organ of a rattlesnake, or even the medium-short tail of a
bull snake. The rapid twitching produces a characteristic sound in dry
vegetation. A racer that vibrates its tail is fully active and
aroused; the sound is heard as the snake pauses before it makes a dash
for shelter. At times the sound probably functions as a decoy to
distract the attention of potential predators, affording the racer an
opportunity to escape.
A racer that is cornered or captured usually puts up a spirited
struggle, striking vigorously and repeatedly at its tormentor. If only
cornered, it will make slashing strokes at the enemy, jerking back to
a coil from each stroke in a manner that causes the teeth to lacerate
the enemy's skin in long scratches if the stroke finds its target. The
rapid recoil often causes teeth to be jerked from their sockets and
left embedded in the wound inflicted by the bite. On many occasions in
sustaining a bite from a racer I have received such teeth which have
remained undetected for a day or more until soreness and festering led
to their discovery and removal. A racer that is grasped may deliver
several bites within a few seconds, chewing vigorously to imbed its
teeth to the maximum at each bite.
If grasped by the tail and held clear of the ground, the racer would
swing its body with a rapid whirling and twisting motion, which in a
few seconds would twist off the end of the tail, unless
countermeasures were promptly taken. Many racers, especially the
larger and older ones, have parts of the tail missing, as a result of
such escapes, and perhaps also from freezing in hibernation or from
certain injuries and infections. If grasped by the body, the racer
struggles with a violent lateral thrashing to break the grip of its
captor, at the same time striking to bite and discharging musk,
urinary wastes and feces.
Many of the racers examined bore scars from wounds that were probably
inflicted by predators. A few had survived severe skeletal injuries,
involving deformation of the spinal column or extensive tearing of
muscle and connective tissue layers of the body wall, altering the
normal body shape. A more frequent type of injury involved chiefly the
integument, which had been ripped open by the teeth, claws, or bills
of adversaries, despite the fact that the skin is remarkably tough and
leathery. Patches of scar tissue with scales in irregular sizes,
shapes and patterns characterized such injuries. The most frequently
observed type of injury involved loss of part of the tail. Usually
only a small terminal part was missing, but occasional stub-tailed
individuals had lost as much as three-fourths of the tail.
No consistent trend of difference between the sexes in incidence of
injuries to the tail was noticeable, but there was definite
correlation with age. In the entire sample from the Reservation and
Rockefeller Tract the percentages in each supposed age group (actually
size group) lacking part of the tail were as follows: hatchlings, 2.9
per cent; one-year-olds, 9.5 per cent; two-year-olds, 15.8 per cent;
three-year-olds, 14.3 per cent; four-year-olds, 15.7 per cent;
five-year-olds, 23.2 per cent; six-year-olds, 30.9 per cent;
seven-year-olds, 28.9 per cent; those eight years old or older, 21.1
per cent. The seeming reversal of trend in the older racers is
difficult to explain, but probably results from inadequate numbers in
this part of the sample.
Although the racer's most characteristic response to any disturbance
is to flee at high speed, certain individuals are inclined to behave
aggressively under exceptional circumstances. Records of such
aggressive behavior nearly all pertain to large individuals of the
northeastern black racer (_C. c. constrictor_) in the breeding season.
Cope (1900:794) wrote: "it is courageous and will sometimes attack,
moving forward with the head raised from 1 to 2 feet above the
ground." Ditmars (1944:13) wrote: "Occasional specimens in the
breeding season ... will actually attack ... glide toward an intruder
... striking madly at one's feet or legs." Woods (1944:257) quoted a
13-year-old amateur herpetologist, Leon Gonthier, regarding the
latter's encounter with an aggressive black racer on May 7, 1944, as
follows: "When I ran toward the snake about 20 feet away, it turned
and came for me. As I bent over to catch it, the snake grabbed me by
the shirt and hung on ... held it off with a stick. It jumped twice
more at me and came clear off the ground." Finneran (1948:124)
describing the species' habits in Connecticut, stated: "A farmer ...
constantly warned me away from Coon Ledge during the spring, saying
the snakes were breeding and would 'chase you.' This very thing
happened. In 1943 a blacksnake followed me for approximately ten feet,
and, in 1946, a male aggressively attacked me for a period of three
minutes. There was ample opportunity for escape."
_Natural Enemies_
Little has been published concerning the natural enemies of the common
racer. The king snake (_Lampropeltis getulus_) is notorious for
ophiphagy, and doubtless preys upon the racer at times. Wright and
Bishop (1915:169) wrote of the king snake in Okefinokee Swamp, in
Georgia, that "all the smaller snakes suffer, and of the larger
species, the blacksnake [racer] and spreading adder are the commonest
prey." However, Clark (1949:252) examined 301 stomachs of king snakes
of this species in Louisiana and found no racers, although many other
kinds of snakes were represented, and, collectively, made up the
greater part of the food.
A rat snake (_Elaphe obsoleta_) found in Leon County, Florida, on June
10, 1924, had a racer in its stomach, according to the Patuxent food
habits file of the U. S. Fish and Wildlife Service. A California
garter snake (_Thamnophis elegans terrestris_) was found to have a
juvenal racer in its stomach (Fitch, 1940:96). A large alligator
lizard (_Gerrhonotus multicarinatus_) was found swallowing a small
racer that had been confined with it in a bag (Fitch, 1935:12).
A few records of predation on blue racers by other reptiles on the
Reservation and Rockefeller Tract were obtained. In 25 scats of the
prairie king snake (_Lampropeltis calligaster_), there were 29
vertebrate prey items of which one was a blue racer. On September 15,
1962, an adult male prairie king snake 49-1/2 inches in length was
found to have a 27-inch yearling racer in its stomach. In 254 scats of
the slender glass lizard (_Ophisaurus attenuatus_) vertebrate remains
were rare, but there were scales and bones of one hatchling blue
racer. Among 21 vertebrate prey items in 14 scats of the timber
rattlesnake (_Crotalus horridus_) there were remains of one blue
racer. Among 589 prey items of copperheads there were two juvenal blue
racers (Fitch, 1960:200). In contrast to these scarce records of
racers in the prey of other snakes, there were more frequent records
of the blue racer preying on its own young. The 1008 food items from
479 racer scats contained remains of 16 racers, small young in most
instances.
Raptorial birds are known to be important predators on snakes.
Breckenridge (1944:118) reported finding remains of a blue racer in
the pellet of a marsh hawk (_Circus cyaneus_). Many pellets of the
marsh hawk collected on the Reservation were all found during the
colder half of the year, and they contained no remains of reptiles.
The same seasonal restrictions applied to the many pellets of four
species of owls that were collected, and these also lacked remains of
reptiles. One of the predators whose food habits have been most
thoroughly investigated on the area is the red-tailed hawk (_Buteo
jamaicensis_). Over the period 1955 through 1962, 1131 pellets of
these hawks were collected, many from the Reservation, but more from
localities scattered throughout the eastern one-fourth of Kansas. The
pellets were those of nestlings and fledglings, nearly all collected
from beneath the nests, in late May, June, or early July. Some 49
different nests were represented, and remains of 43 blue racers were
found. In one nest which yielded a total of 191 food items, racer
remains occurred 13 times, but no other nest yielded records of more
than three racers, and some other species of reptiles, notably the
black rat snake (_Elaphe obsoleta_) comprised much more important
components of the food. Since only one meal in 26 contained remains of
racers, it seems that a red-tailed hawk would destroy only a few
racers in the course of a year on its territory of perhaps half a
square mile, and that its predation would not be a major factor in the
racer's ecology.
That the red-tailed hawk is a natural enemy to be reckoned with
throughout the racer's extensive range was demonstrated by the
analysis of contents of 116 stomachs from localities well scattered
over the United States and Canada. Among the 152 vertebrate prey items
represented there were three racers: a juvenile _C. c. constrictor_
from Stag Lake, New Jersey, October 16, 1927; a _C. c. mormon_ from
Weiser, Idaho, April 11, 1930, and a _C. c. stejnegerianus_ from San
Roman, Cameron County, Texas, in the spring of 1938. Because of the
widely scattered geographical origin of these stomachs, a remarkably
large number of species of prey were represented, and no one species
predominated. Small mammals of the genera _Sylvilagus_,
_Spermophilus_, and _Thomomys_ comprised the most important component
of the food; the only other reptile so well represented as the racer
was the common garter snake (_Thamnophis sirtalis_) which likewise had
three occurrences.
In June and July, 1954, a nest of broad-winged hawks (_Buteo
platypterus_) on the Reservation yielded 71 prey items of which seven
were blue racers. At least 19 species of prey were represented,
although specific determinations were not possible in some instances.
The prairie vole with eight records was the most frequent prey, and
the racer and cardinal (nestlings) each had seven, while all other
species were represented by fewer occurrences. Six of the racers were
first-year young but the remaining one was thought to be an undersized
second-year individual. Although an adult racer, especially a large
one, would probably be an adversary too powerful to be killed and
eaten by a broad-winged hawk, this hawk is perhaps one of the more
important natural enemies of the first-year young in the eastern
United States.
Further records of predation on racers by raptors were obtained from
the U. S. Fish and Wildlife Service files through the kindness of Dr.
Wm. H. Stickel. There were three records of such predation by
red-shouldered hawks (_Buteo lineatus_) from Lunenberg, Massachusetts,
May 1, 1896; Portland, Maine, March 16, 1906; and 65 miles northeast
of Sarasota, Florida, June 10, 1918. There were two records of
predation by broad-winged hawks from Catlettsburg, Kentucky, July 26,
1910, and Portland, Connecticut, May 18, 1912. There were four records
of predation by marsh hawks on racers--Peck's Island, Maine, September
18, 1903; Edgartown, Massachusetts, April 12, 1912; West [Tisbury?],
Massachusetts, July 31, 1912; and Okanagan Landing, British Columbia,
June 5, 1918. A sparrow hawk (_Falco sparverius_) from De Ranch,
Wyoming, May 27, 1910, had eaten a racer, as had a barn owl (_Tyto
alba_), from Franklin County, Kansas, November 16, 1922, and a crow
(_Corvus brachyrhynchos_, nestling) from Onaga, Kansas, May 16, 1914.
Perhaps certain mammalian predators are even more important natural
enemies than are raptorial birds, but records of predation on racers
by mammals are few. Substantial samples of scats of opossums and
coyotes from the Reservation have contained no remains of racers. The
Fish and Wildlife Service files include a record of an opossum from
Adrian, Michigan, on April 26, 1934, that had racer remains in its
stomach. No racers were specifically recorded from a collection of 820
scats and 22 stomachs of raccoons (_Procyon lotor_) from Douglas
County, Kansas, reported upon by Stains (1956:43), but occurrences of
unidentified snake may have pertained in part to the racer. Skunks are
probably more important natural enemies, but food habits data from the
Reservation are lacking for the two kinds of skunks occurring there.
Crabb (1941:356) in a study of the food habits of the spotted skunk
(_Spilogale putorius_) in southeastern Iowa, did not report any
reptiles among the many kinds of prey found in scats. Several times in
many years of residence near Medford, Jackson County, Oregon, I saw
remains of racers which appeared to be victims of striped skunks
(_Mephitis mephitis_). Tracks and other sign of the skunks were often
noticed along a little-used road on a hillside, passing between a
pasture and a hay field, with an oak grove, high weeds, and brush,
bordering the road. The racers sometimes found as victims along this
road were small- or medium-sized individuals. In every instance the
predator had begun eating on the tail end of the snake, and later had
abandoned the remains leaving the head and part of the forebody still
intact. Predation had occurred at night. Skunks foraging mostly in
twilight or darkness, probably find racers inactive beneath flat rocks
or in shallow burrows. The skunks would be too slow and clumsy to
catch the snakes in the open when they were fully active.
The funnel traps used for catching the racers also caught many other
kinds of animals. Often a racer and another kind of snake were caught
together, but, ordinarily, in these instances no damage to either
resulted, although racers, copperheads, king snakes, and garter snakes
are all known to eat each other's young. At times, large predatory
ground beetles (_Calosoma scrutator_ and _Pasimachus_ sp.) were
so abundant that a dozen or more were caught together in a trap,
and several times such groups attacked and killed and partly
ate young racers caught in the same traps. White-footed mice
(_Peromyscus leucopus_), deer mice (_P. maniculatus_), harvest
mice (_Reithrodontomys megalotis_), short-tailed shrews (_Blarina
brevicauda_), and least shrews (_Cryptotis parva_) all were caught
rather frequently in the traps, and each, on one or more occasions,
gnawed and killed or severely injured a racer trapped with it. The
attacks probably were motivated by hunger in all instances, the snake
in some instances failing to defend itself or escape because of low
temperature. Occasionally such encounters might occur even under
natural conditions, the mouse or shrew finding and attacking the snake
while the latter was torpid and helpless in its hibernaculum or in a
more superficial temporary shelter.
_Disease_
Relatively few of the racers examined showed signs of disease. The
most common type of affliction was an infection of the skin causing
cankerlike sores, chiefly on the ventral plates, sometimes on the head
or tail. These were seen most often in snakes recently emerged from
hibernation, but persisted later in the season in years of
exceptionally wet weather. Some of the racers most severely afflicted
appeared to be in debilitated condition. The causal organism was not
determined, nor was it definitely determined whether this type of
disease causes mortality.
_Parasites_
The ectoparasites of the racer are chiefly chiggers, the parasitic
larvae of mites. Loomis (1956) in his study of the chigger mites of
Kansas examined many of the racers captured in the early years of my
field work. He checked a total of 130 racers, mostly from the
Reservation, and found four different species of chiggers, all of the
genus _Trombicula_: _T. alfreddugèsi_, _T. lipovskyana_, _T.
kansensis_ and _T. sylvilagi_. The common pest chigger, _T.
alfreddugèsi_, parasitizes most of the species of reptiles, birds, and
mammals occurring in Kansas, and it was by far the most common kind on
the racers. The numbers per racer in different months were as follows:
June, 81; July, 285; August, 432; September, 123; October, 15. Many of
the racers were collected in the relatively cool and moist summers of
1950 and 1951. In a year of typical weather, heaviest infestations
occur in early summer, June or the first half of July, and the numbers
taper off rapidly in the hot but often dry weather of late July,
August, September, and October. In hot, humid weather of early summer
a racer may have several hundred chiggers attached to it, filling most
of the areas of exposed skin between the scales. The chiggers are
conspicuous because of their bright orange color. Like _T.
alfreddugèsi_, _T. lipovskyana_ was also found in large numbers on
racers and is found on many kinds of hosts. Loomis (_op. cit._:1281)
recorded it from one kind of frog, one kind of toad, one kind of
turtle, two of lizards, six of snakes, 19 of birds, and nine of
mammals from eastern Kansas. Five larvae of _T. sylvilagi_ were
recorded from a racer captured in October. That kind of chigger is
primarily a parasite of small mammals, and perhaps cannot develop
successfully when it attaches to a snake. Unlike most other kinds of
chiggers, this species is most in evidence in autumn and winter. A
single larva of _T. kansensis_ was found on a racer in October. This
relatively rare kind of chigger has been found on several kinds of
snakes and small mammals (including pocket gophers) and is known from
hot and dry rocky places. Even the racers that were heavily loaded
with chiggers showed no obvious ill effects, but the chiggers are
potentially vectors of various diseases.
Of the many endoparasites found in racers, the lung fluke, _Neorenifer
lateriporus_ was the only one identified and frequently observed in my
study (Stewart, 1959). This is a digenetic trematode of the subfamily
Reniferinae. The racer is its specific host. The life history is still
unknown, but in other members of the subfamily, all of which
parasitize snakes, an aquatic snail and a frog are required as hosts
at different stages of the life cycle. Presumably _N. lateriporus_ has
similar requirements. The two common local water snails, _Heliosoma
trivolvis_ and _Physa anatina_, are both potential hosts. By far the
most probable frog host is the leopard frog. In wet weather of July
the recently metamorphosed leopard frogs leave the water and disperse
to all habitats, probably carrying with them the parasites acquired in
the tadpole stage. The racers in turn probably acquire their flukes by
eating the young frogs in summer. In any case, the adult racers are
nearly all parasitized, but the flukes have not been found in those
racers that were less than one year old. During their first few
months, the racers are too small to swallow leopard frogs, even the
young. The flukes have been seen in the live racers mostly in May,
when most adults are infested with the flukes. Seemingly at this
season the flukes migrate forward into the mouth of the host.
Probably this is the time when the flukes breed and lay eggs; if so,
the eggs would pass through the digestive tract of the snake and
escape with its feces. The latter are usually left in terrestrial
situations unfavorable for the development of an aquatic stage, but
perhaps some of the eggs are washed into ponds by heavy summer rains.
In late summer and fall the flukes are not to be found in the mouths
of the live snakes.
Most complete records of the flukes present in racers were kept in
1959. The following table shows the numbers of racers examined and the
percentage having flukes in that year.
Ortenburger (1928:182) recorded lung flukes (_Renifer ellipticus_)
from blue racers. In Maryland, McCauley (1945:76) also recorded
numerous lung flukes (_Pseudorenifer_ sp.) in an immature racer 490
millimeters in total length. Parker (1941:34) recorded _Neorenifer
septicus_ from racers collected at Reelfoot Lake, Tennessee,
Greensboro, Georgia, and Kissimmee, Florida; also he recorded _N.
georgianum_ from racers collected at Reelfoot Lake. _N. septicus_ was
recorded by the same author from the water moccasin (_Agkistrodon
piscivorus_) and _N. georgianum_ was also recorded from the king snake
(_Lampropeltis getulus_).
Cloacal smears from the racers examined usually showed an abundance of
ciliate protozoans, either parasites or commensals, and occasionally
nematode worms. Harwood (1933:66) examined two racers from the
vicinity of Houston, Texas, and found four kinds of helminths:
_Kalicephalus agkistrodontis_, _K. rectiphilus_, _Ophidascaris_ sp.,
and _Polydelphis_ sp. Each parasite was found in only one of the two
snakes. McCauley (_loc. cit._) recorded nematodes (_Physaloptera
obtusissima_) from black racers in Maryland, and Ortenburger (_loc.
cit._) recorded _Physaloptera_ sp. from the blue racer.
Table 18. Seasonal Incidence of the Fluke Neorenifer lateriporus,
in Mouths of Blue Racers on the Reservation and Rockefeller Tract
=============+=================+======================
| Number of | Percentage of sample
| racers checked | having flukes
-------------+-----------------+----------------------
Apr. 15-30 | 1 | 100
May 1-15 | 28 | 79
May 15-31 | 25 | 72
June 1-15 | 24 | 50
June 15-30 | 17 | 18
July | 30 | 0
Aug. | 5 | 0
Sept. | 9 | 0
Oct. | 2 | 0
-------------+-----------------+----------------------
Populations
_Composition_
Since there is a brief annual breeding season, any local population of
racers consists of a series of discrete annual age groups. The
population reaches its annual maximum in early September, after
undergoing sudden increase by the addition of the annual crop of
hatchlings. Throughout the remainder of the year numbers of racers
undergo gradual reduction as a result of the many combined mortality
factors that affect them. This mortality is distributed among all the
age classes, but the heaviest losses, both percentage-wise and in
actual numbers, are sustained by the first-year young. Being by far
the most numerous group, these young suffer more mortality than all
the other age classes combined. Presumably much of this mortality is
concentrated in the early weeks of life, while the young are still
near their minimum size; the rate of loss is gradually reduced as
larger size is attained and some of the early hazards are outgrown. In
the adult age classes also, the larger and older snakes live in
greater security, and the rate of mortality is higher in the smaller
and younger snakes. Even before hatching, the eggs are subject to
heavy losses from predators, and probably from drying, flooding, and
other unfavorable climatic factors. Unfortunately it was not possible
to obtain definite figures on any of these losses since the eggs were
never found under natural conditions and the hatchlings were seen only
in relatively small numbers.
The records obtained from trapping racers in late spring and summer in
fields provided a somewhat different picture of the population from
the sample obtained along the ledges in autumn. In the former sample
there were 400 males to 257 females, but in the latter sample there
were 355 males to 379 females. I regard the summer sex ratio as a
distorted one, brought about by the greater activity of the males in
the breeding season. Racers are caught most easily in May, and the
fact that two or more males often were trapped with the same female,
while the reciprocal combinations did not occur, demonstrates the
increased activity of the males in their search for mates at this
season. In autumn there is no sexual activity; both sexes probably are
equally active in seeking places to hibernate when they are trapped
along the hilltop outcrops. The ratio of 51.6 per cent females in my
sample of 734 may indicate that in the males greater activity at other
seasons results in a somewhat higher mortality. This idea is borne out
by the fact that for the supposed two-, three- and four-year-olds
combined, females comprise 51.2 per cent, but they comprise 55.6 per
cent of those more than four years old and 61.3 per cent of those more
than five years old.
[Illustration: Fig. 20. Histograms comparing snout-vent length in
random samples of _Coluber c. flaviventris_ (those captured on the
Reservation and Rockefeller Tract in 1960 and 1961) and _C. c. mormon_
(specimens in the Museum of Vertebrate Zoology, University of
California). In the museum sample, collected by conventional methods,
the first-year young constitute a prominent and fairly distinct size
group, whereas in the sample of racers from the Reservation and
Rockefeller Tract, mostly caught in wire traps of quarter-inch mesh,
relatively few young were secured. It is demonstrated that hatchlings
are approximately the same length in both populations, but
_flaviventris_ grows much longer, and that the differences in length
between the sexes is approximately the same in each population.]
By assigning to each racer caught an arbitrary age, on the basis of
size according to Table 17, I calculated the population (exclusive of
those snakes in their first year of life) to have the composition
shown in Table 19.
Table 19. Percentages of Adult Population of Blue Racers Comprised
by Each Annual Age Group
=================+===============
| Percentage of
Years of Age | population
-----------------+---------------
2 | 41.5
3 | 17.8
4 | 12.6
5 | 9.5
6 | 6.1
7 | 4.3
8 | 2.7
9 | 2.4
10 | 1.2
11 or more | 1.9
-----------------+---------------
Figures are completely lacking to show the relative numbers of
juveniles, until, already approaching adult size, the young are about
to enter their second hibernation. My combined fall samples include
303 of these latter young, as against 142 racers about to enter their
third hibernation. Thus, after having nearly attained adult size,
these adolescent snakes sustained a loss of 53 per cent in a year.
Losses must occur at an even more rapid rate in the younger and
smaller snakes. It may be speculated that of the approximately 300
eggs produced by a population of 100 adult racers, 150 are lost before
or during the period of incubation which lasts nearly two months. Of
the 150 hatchlings emerging in early September, at least one-third
probably are eliminated by the following breeding season in late May,
leaving 100. The 100 survivors at this stage are still small
juveniles, but by autumn they have attained adolescent size. By this
time, if they had undergone a further reduction by 53 per cent, only
47 would remain--approximately the number to be expected if the
population were stable from year to year.
A notable difference between the fall sample and the spring sample
that I obtained was the higher proportion of large and old racers in
the former sample. This difference can be attributed to the
year-to-year changes in the population during the 14 consecutive years
spanned by my field work. The fall sample of 734 racers represented
the combined catch of the years 1949 through 1962, rather evenly
distributed, but the spring sample included few snakes from the years
1949 through 1957; most were from the years 1958 through 1961. In
1949 when the study was begun, the Reservation was being protected for
the first time, and formerly overgrazed pastures or cultivated fields
were acquiring a rank growth of grass and weedy vegetation, and thus
becoming favorable habitat. The abundant new habitat promoted rapid
increase in the population of racers until the newly available areas
were filled to their "carrying capacity." Table 21 shows the changing
trends of the different age groups. Although the separate annual
samples are perhaps too small to show the composition of the
population accurately, it is significant that in the fall of 1949 an
unusually high proportion of the racers caught were one-year-olds,
hatched in September, 1948.
Table 20 shows that in a typical group of 100 subadult and adult
racers (second year and older) only a little more than one-fourth are
productive females. The largest females, six years old and older,
making up less than ten per cent of the adult population, contribute
nearly half the total complement of eggs.
The calculated number of eggs pertains to a stage before oviposition,
and subsequent losses through resorption under unfavorable conditions,
through inviability of embryos and through deaths of some of the
gravid females, are to be expected. In the weeks of incubation further
losses are sustained. Although these losses cannot be measured, they
must be severe as on numerous occasions scattered and torn eggshells
representing entire clutches dug out and destroyed by predators, have
been found. Probably other clutches are destroyed underground by such
predators as moles and egg-eating snakes, and still others by insects.
Tinkle (1959:195) wrote that in a clutch of 15 eggs found under a
board, four were parasitized and had small perforations. Molds destroy
a high percentage of all reptilian eggs that are incubated
artificially and doubtless destroy many under natural conditions also.
Excessive heat or moisture, or desiccation, resulting either from
climatic extremes or from poor choice of a nest site by the female,
would cause further loss. In four different years, Blair (1960:108)
found that losses of eggs between laying and hatching in the Texas
spiny lizard (_Sceloporus olivaceus_) ranged from 69 per cent to 86
per cent; no other comparable study of the extent of egg losses in a
species of reptile is known to me. The racer is somewhat less prolific
than the spiny lizard, and potentially longer lived; the racer's eggs
are larger and thicker-shelled, and they are deposited in deeper
burrows. It might be expected that losses during incubation would be
somewhat less in the racer than in the spiny lizard.
Table 20. Calculated Productivity in a Hypothetical Group of 100
Subadult and Adult Blue Racers
===========+==============+============+============+============+=========
| Percentage | Percentage | Percentage | Eggs |
Age-Group | of | of fecund | productive | per | Number
(years) | population | females in | females in | productive | of eggs
| in age-group | age-group | age-group | female | produced
-----------+--------------+------------+------------+------------+---------
2 | 41.5 | 51.2 | 13 | 9.2 | 26
3 | 17.8 | 51.2 | 56 | 9.9 | 51
4 | 12.6 | 51.2 | 60 | 10.8 | 42
5 | 9.5 | 55.0 | 57 | 13.0 | 39
6 and over | 18.6 | 61.3 | 80 | 15.7 | 143
-----------+--------------+------------+------------+------------+---------
Table 21. Percentages of Racers in Each Annual Age Group (Exclusive of
Hatchlings) in Autumnal Samples at Different Stages of the Field
Study, Showing Shift Toward Older Age-Groups in the Later Years
==============+=========================================================
| Year or combination of years represented by each sample
+-----------+-----------+-----------+----------+----------
| 1949 | 1950 | 1953 | 1956 | 1959
Years of Age | | 1951 | 1954 | 1957 | 1960
| | 1952 | 1955 | 1958 | 1961
| | | | | 1962
--------------+-----------+-----------+-----------+----------+----------
1 | 54 | 44 | 39 | 39 | 41
2 | 14 | 24 | 21 | 19 | 19
3 | 18 | 11 | 23 | 16 | 13
4 | 4 | 10 | 10 | 11 | 9
5 | 6 | 6 | 3 | 8 | 8
6 | 2 | 1 | 3 | 1 | 3
7 | 2 | 4 | 4 | 2 | 3
8 | ...... | ...... | ...... | .5 | 2
9 | ...... | 1 | .4 | .5 | 2
10 | ...... | ...... | .4 | 2 | 1
Older than 10 | ...... | ...... | ...... | .5 | .....
| | | | |
Number in | | | | |
sample | 49 | 126 | 117 | 194 | 242
--------------+-----------+-----------+-----------+----------+----------
Although figures for the youngest age groups--one-year-olds and
hatchlings--are missing, approximations of them may be furnished by
extrapolation, from the information available regarding the
productivity of the population. Some factors involved in productivity
are that the sex ratio deviates from parity, slightly in favor of the
females in the adolescents but more markedly in favor of the females
among the older age groups; that some adult females apparently fail to
produce eggs in the breeding season, but the percentage decreases in
the older snakes; and that number of eggs per clutch increases in
proportion to the size and age of the female producing them. Too few
figures are available concerning most of these factors to indicate
more than the trends; nevertheless the available figures have been
used in Table 20 in an attempt to estimate the productivity of a
hypothetical population.
_Numbers_
Conant (1938:178, Pl. 7) published a photograph of 106 blue racers
killed in February, 1932, by farmers near Bellville, Ohio, and Pope
(1944:173) mentioned that scores of blue racers aggregated in October
around an oak-covered dune near Chicago. In both these instances large
hibernating aggregations were involved, and the areas represented by
them are unknown; nothing has been recorded regarding population
densities.
The records obtained through my fall trapping, along hilltop rock
outcrops, yielded no information concerning population densities, but
those obtained in fields in summer did provide significant information
in this regard. Even after years of trapping on the same area, the
catch still consisted largely of new individuals; the method was not
sufficiently effective to catch all racers present at any one time,
and the total catch for a season therefore provided only a crude index
of the minimum number present.
The summer trapping was carried on in three separate areas. One of
these was the area of bottomland pastures and formerly cultivated
fields where the Reservation headquarters are located, a block of 39
acres bounded on three sides by woodland, and on the fourth by
cultivated farm land. Effective trapping in this area was carried on
through the years 1955 to 1961 inclusive. A second area, of 48 acres,
was one of upland fields, mostly covered with re-established prairie
grasses, in the northeastern part of the Reservation. A third area, of
137 acres, also upland, was that of the Rockefeller Tract, cultivated
through 1956 and sown to prairie grasses the following year, and the
adjacent northwestern hilltop portion of the Reservation. Effective
trapping on these two latter areas was carried on in 1958 through
1962.
For the seven years of trapping in the House Field area, the catch was
as follows: 30, 33, 38, 38, 34, 24, and 20. In four years of trapping,
the northeast field area yielded 42, 28, 37, 59, and 19 blue racers,
and the Rockefeller Tract yielded 52, 67, 67, 126, and 106. The actual
catch was hence less than one per acre in nearly all instances, but
the year-to-year differences in catch are believed to be caused
chiefly by differences in numbers of traps used and in trapping
effort, rather than by changes in the numbers of racers present.
Best index to the number of racers actually present is provided by the
number of recaptures, and their ratio to first captures. The
population of course, undergoes alteration from year to year, with
many racers eliminated and replaced by others.
In 1955, 26 racers were caught in the May-June-July period, in the
headquarters field area. In the August-September-October period of the
same year five racers were caught of which only one was a member of
the original 26. The five-to-one ratio indicates that the original 26
may have represented an actual population of 130, but of course the
single recapture is much too small a sample to provide a reliable
ratio. Some of the racers caught in May were recaptured in June,
others in July, and still others not until late summer or early
autumn. Somewhat different estimates can be obtained for the
population depending on how the season's records are divided. For
instance, in the headquarters field area in May 1955, eleven racers
were caught; in the remainder of the season 20 were caught, of which
two were members of the original group of eleven. The 20 to 2 ratio
indicates that the 11 caught in May represented an actual population
of 110. In the period May-June, 18 racers were caught, and in
July-August-September-October, 15 were caught, including four of the
original 18, hence indicating a population of 67. Although obviously
the population underwent some change during the course of the season,
the three sets of census figures apply essentially to the same
population, and the divergence in them illustrates the wide range of
error arising from insufficiently small samples.
Common sources of error in the censusing of natural populations of
animals by the capture-recapture method ("Lincoln Index" or "Petersen
Index") arise from the fact that the composition of a local population
often changes between two sampling periods, or even within them. Some
of the animals marked may move elsewhere, to be replaced by unmarked
immigrants, or they may die and be replaced by unmarked maturing
young. First-year racers that could pass through the quarter-inch mesh
of the traps in spring and early summer became too large to escape in
this way in the latter half of the summer, but these young were
excluded from the census computations. There was doubtless some
shifting of marked individuals away from the study areas and shifting
of new individuals onto these areas in the periods of weeks between
successive samplings. Jackson (1939) has explained a method of
correcting census computations based on capture-recapture ratios when
there is a consistent trend of diminishing recaptures with increase in
elapsed time. However, in my records no such trend is discernible;
furthermore it has been demonstrated that individual racers tend to
stay within the same home range area throughout most of their season
of activity. Therefore, I conclude that shifts of individuals away
from the study areas or into them, in the intervals between samplings
constitute only a minor source of error.
A combination of the figures from the three samples listed above
provides an intermediate "smoothed" figure that can be accepted with
somewhat more confidence than any one of the separate censuses because
it is based on more records. The combined ratios indicate a total of
105 racers in the headquarters field area. The figures obtained in the
different sampling periods, and the census figures derived from their
ratios are shown in tables 22 and 23. Differences from year-to-year in
the census figures for any one area show no consistent trends and
their variation is similar to that shown in different samples for the
same season. Probably populations were fairly stable throughout the
periods involved. If such stability is assumed, the samples from
different years may be combined, and the composite figures derived
from them may be accepted with more confidence. For the headquarters
field area, for instance, 419 records of racers were gathered in all
the preliminary sampling periods of the seven seasons involved; the
records totalled 263 for all the secondary sampling periods, with 70
recaptures in secondary periods of the snakes recorded in the
corresponding preliminary periods. A population of 75 racers is
indicated--1.9 per acre. Corresponding figures for the northeast field
area are: preliminary samples 453, secondary samples 163, recaptures
39, calculated number 135 (2.82 per acre). For the Rockefeller Tract
the figures are as follows: Preliminary samples 807, secondary samples
476, recaptures 126, the ratio indicating a population of 153, or 1.11
per acre.
These figures represent the number of adults present in early summer
when the population is near its annual low point. The first-year
young, excluded from this census because they cannot be caught in
representative numbers, perhaps approximate the number of adults, in
May, so the figures obtained would need to be approximately doubled to
be representative of the entire population. By late summer the
adults, and especially the yearlings, have undergone substantial
reduction in numbers, but in late August and early September the
hatching of a new crop of young increases the population to its annual
maximum. The maximum numbers probably are about three times those
obtained by censusing adults in early summer. The peak population of
late summer or early autumn is estimated to consist of hatchlings,
comprising somewhere near 50 per cent; adults, comprising a little
more than 25 per cent; and yearlings comprising a little less than 25
per cent.
Table 22. Captures Recorded and Population Calculated From Them on
Hilltop Grassland Areas of Rockefeller Experimental Tract and
Adjacent Reservation in Four Different Years
==========================+======+======+======+======+===========
| | | | | Four-year
| 1959 | 1960 | 1961 | 1962 | average
--------------------------+------+------+------+------+-----------
_First Census_: | | | | |
Early May | 0 | 8 | 21 | 32 | 61
Late May | 3 | 13 | 33 | 35 | 84
Recaptures | 0 | 1 | 2 | 7 | 10
Estimated population | | 104 | 346 | 160 | 128
| | | | |
_Second Census_: | | | | |
May | 3 | 25 | 54 | 59 | 141
June | 9 | 6 | 25 | 40 | 80
Recaptures | 0 | 3 | 6 | 24 | 33
Estimated population | | 50 | 165 | 99 | 85
| | | | |
_Third Census_: | | | | |
May-June-July | 25 | 34 | 94 | 100 | 253
Sept.-Oct | 8 | 13 | 20 | 13 | 54
Recaptures | 1 | 3 | 5 | 4 | 13
Estimated population | 200 | 182 | 376 | 324 | 263
| | | | |
_Fourth Census_: | | | | |
May-June | 31 | 30 | 73 | 76 | 210
July-Aug.-Sept.-Oct | 24 | 15 | 34 | 35 | 108
Recaptures | 3 | 2 | 14 | 12 | 31
Estimated population | 104 | 225 | 177 | 222 | 183
| | | | |
_Fifth Census_: | | | | |
May | 3 | 25 | 54 | 60 | 142
June to October | 23 | 20 | 67 | 40 | 150
Recaptures | 0 | 5 | 14 | 20 | 39
Estimated population | | 100 | 258 | 120 | 162
| | | | |
_Five Sets Combined_: | | | | |
Combined first samples | 62 | 122 | 296 | 327 | 807
Combined second samples | 67 | 67 | 179 | 163 | 476
Recaptures | 4 | 14 | 41 | 67 | 126
Estimated population | 208 | 117 | 258 | 159 | 153
--------------------------+------+------+------+------+-----------
Densities in early summer of one to three adult blue racers per acre
probably are typical of the better types of habitat in the region of
my study. The upland field area estimated to have 2.82 racers per acre
was better habitat than the other two study areas. Prior to 1948 it
had been cultivated and severely eroded. In 1949 most of it was sown
to seeds of prairie grasses, and by 1958 different parts of it were
dominated by different species of native perennial tall grasses
interspersed with areas that supported a weedy type of vegetation, and
other areas that supported dense thickets of sumac, dogwood, elm
saplings, or other woody plants. The abundance and diversity of dense
cover and of small animals made this area especially favorable habitat
for the racer.
Table 23. Captures Recorded and Populations Estimated From Them in
Headquarters Field Area of Reservation
Column headings:
A: 1955
B: 1956
C: 1957
D: 1958
E: 1959
F: 1960
G: 1961
H: Seven-year average
==========================+=====+=====+=====+=====+=====+=====+=====+====
| A | B | C | D | E | F | G | H
--------------------------+-----+-----+-----+-----+-----+-----+-----+----
_First Census_: | | | | | | | |
May | 11 | 21 | 7 | 24 | 17 | 13 | 6 | 99
June-July-Aug. | 20 | 11 | 25 | 20 | 22 | 12 | 14 | 124
Recaptures | 2 | 1 | 4 | 5 | 5 | 2 | 0 | 19
Estimated population | 110 | 231 | 44 | 96 | 75 | 78 | ... | 92
| | | | | | | |
_Second Census_: | | | | | | | |
May-June | 18 | 25 | 17 | 28 | 27 | 15 | 13 | 143
July-Aug.-Sept.-Oct | 15 | 8 | 17 | 15 | 15 | 11 | 8 | 89
Recaptures | 4 | 1 | 7 | 5 | 9 | 3 | 1 | 30
Estimated population | 68 | 200 | 41 | 84 | 45 | 55 | 104 | 61
| | | | | | | |
_Third Census_: | | | | | | | |
May-June-July | 26 | 28 | 22 | 31 | 31 | 20 | 19 | 177
Aug.-Sept.-Oct | 5 | 7 | 13 | 12 | 6 | 5 | 2 | 50
Recaptures | 1 | 2 | 7 | 5 | 3 | 1 | 1 | 20
Estimated population | 130 | 128 | 47 | 87 | 63 | 75 | 148 | 63
| | | | | | | |
_Three Sets Combined_: | | | | | | | |
Combined first samples | 55 | 74 | 46 | 83 | 75 | 48 | 38 | 419
Combined second samples | 40 | 26 | 55 | 47 | 43 | 28 | 24 | 263
Combined recaptures | 7 | 4 | 18 | 15 | 17 | 6 | 3 | 70
Estimated population | 105 | 160 | 47 | 87 | 63 | 75 | 101 | 75
--------------------------+-----+-----+-----+-----+-----+-----+-----+----
[Illustration: PLATE 19
Fig. 1. Head of hatchling blue racer, dorsal view, September 1962,
approximately × 3.
Fig. 2. Head of hatchling blue racer, lateral view, September 1962,
approximately × 3.
Fig. 3. Head of yearling male blue racer, lateral view, August 1,
1961, a little less than twice natural size.
Fig. 4. Head of adult male blue racer, lateral view, July 16, 1961,
approximately × 2. All three snakes from Rockefeller Experimental
Tract, Jefferson County, Kansas.]
[Illustration: PLATE 20
Fig. 1. Abandoned limestone quarry on a hilltop of southward exposure
on The University of Kansas Natural History Reservation, in late
autumn of 1951. The crevices along the base of the ledge provided
favorite hibernating sites for blue racers.
Fig. 2. Hatchling blue racer and eggshell from which it had recently
emerged, in early September, 1962; × approximately 1-2/3.]
[Illustration: PLATE 21
Fig. 1. Wire funnel trap set at base of hilltop limestone outcrop in a
spot strategically located for interception of blue racers searching
for deep crevices in which to hibernate, October 15, 1949.
Fig. 2. Large clutch of 21 blue racer eggs, recently plowed out, at
Harold Brune farm, Jefferson County, Kansas, July 10, 1962.]
[Illustration: PLATE 22
Fig. 1. Habitat of blue racer, blue-stem prairie on Botany Bluff at
northwest corner of the University of Kansas Natural History
Reservation, looking south. Trees and brush in background are along
limestone outcrop at top of slope. Mowed area in foreground is
southwest corner of Rockefeller Experimental Tract, a privately owned
farm at the time this photograph was taken in the summer of 1951.
Fig. 2. Habitat of blue racer, blue-stem prairie on south slope of
Botany Bluff, looking north along west edge of the Reservation, summer
of 1951. By 1962, with exclusion of fire, and protection from mowing,
prairie vegetation had largely disappeared from this slope, and had
been replaced by trees and brush. As a result of these successional
changes racers no longer found this slope a suitable habitat in
summer, but they continued to resort to the hilltop rock outcrop to
hibernate in autumn.]
Some local areas probably support higher populations of racers than do
areas where censuses were made, but under modern conditions,
situations that offer near optimum habitat are not likely to be
extensive or to persist long. On land that is capable of producing a
good crop of vegetation, the crop is usually harvested either by
grazing of livestock or by using the land for cultivation, with the
result that the racers are, at least in some seasons, forced into
marginal situations. More than 50 years ago in Missouri, Hurter
(1911:170) wrote that the racer "was quite common 20 years ago in
pastures, meadows and fields but as cultivation has advanced it is
becoming quite rare." In 1962 the widespread and adaptable blue racer
is still common in many parts of its range, including Missouri, but in
most places its population densities probably are lower than formerly.
Reduction since 1911 has probably been far more drastic than the
reduction that had occurred up to that time. Schmidt and Necker
(1935:69), writing of the racer in the Chicago region, noted "the
snakes which raise their heads and face mowing machinery tend to be
exterminated in agricultural areas." They stated that in the Chicago
region the racer had been exterminated by the advance of agriculture
except in two extensive sand dune areas. In July 1962, Mr. V. B.
Howell, a progressive farmer of the Great Bend area in central Kansas,
told me that the kinds of snakes inhabiting cultivated land--blue
racer, bull snakes, prairie king snakes, hog-nosed snakes, and
others--had undergone great reduction in numbers during the period of
his farming. He estimated that in a forty-year period the numbers had
declined to perhaps five per cent of their level in the area most
familiar to him, centering at his farm 11 miles northwest of Great
Bend, Barton County. In accounting for this change in population
density Howell pointed out the relative destructiveness to small
animals of modern farm machinery as contrasted with horse-drawn
equipment or that used with tractors of earlier models. Modern
tractors move forward so rapidly that there is little opportunity for
snakes or other small animals to avoid them, and the plows and disks
cut wide swaths penetrating more deeply into the soil than did older
types. On July 10, 1962, in searching the furrows of a freshly plowed
small field on the Harold Brune farm, for turned-up nests of the
snakes, I found two adult blue racers that had been struck and killed
by the plow, possibly while they were underground. In fields that are
plowed or cultivated between the times of egg-laying and hatching, the
eggs are destroyed. Because of its rapid movements and alertness, the
racer is more likely to escape farm machines than are most other
kinds of snakes. Nevertheless, it is vulnerable and survives in
cultivated areas only when they are interspersed with pastures,
woodlots, or streamside thickets where at least part of the population
may find refuge.
Summary
Field study of the blue racer was carried on in several localities in
Kansas, but chiefly at the University of Kansas Natural History
Reservation (the northeasternmost section of land in Douglas County),
and the adjacent 160-acre Rockefeller Experimental Tract in Jefferson
County. By October 26, 1962, after 14 years of field work, a total of
1423 racers had been captured some 2197 times.
The locale of the present study was near the geographic center of the
blue racer's range. The range, chiefly in the Mississippi Valley and
Great Plains region, is centrally situated with respect to the other
seven subspecies. An extensive but scattered literature concerning the
ecology of the species as a whole, and its several geographic races,
has been reviewed and utilized for comparison with my own field data.
Blue racers were caught in wire funnel traps set in prairie and
pastureland habitat in summer, and along hilltop limestone outcrops in
woodland in autumn. The autumn trapping along rock outcrops was
carried on each year from 1949 to 1962, but effective summer trapping
was carried on only in the last six years of the study. Each racer
caught was individually and permanently marked by scale clipping. More
than half were caught only once, but many were recorded repeatedly,
with a maximum of 16 captures.
The racer occurs throughout most of the United States, and its
populations are subject to much geographic variation. The snakes are
largest in the northeastern part of the range, with clines of
decreasing size toward the southeastern, southern and western parts of
the United States. There are somewhat parallel trends in coloration;
the black racer of the northeastern states grades into paler, gray or
light brown subspecies in southern Florida, Texas, and the far western
states. Accompanying these changes in color and size are minor
morphological changes and major ecological changes. The black racers
of the eastern states often inhabit forest or forest-edge habitats
while the paler and smaller snakes of more southern or western areas
typically inhabit scrub, chaparral, or prairie. The large,
dark-colored racers of the eastern and northeastern states are
especially inclined to attack larger prey including small
vertebrates, even weasels, rabbits, and chipmunks, whereas the
smaller and paler racers of more southern and more western areas take
a higher proportion of insects and rarely attack vertebrates other
than small reptiles.
On the area where field work was carried on in northeastern Kansas,
tall-grass prairie habitat is preferred, but fields of grain or
alfalfa, grazed pasture, brush, woodland edge, groves or open
woodland, and weedy fields are all utilized to some extent. The racer
is strictly diurnal and largely terrestrial but it may climb through
bushes or small trees in foraging or escaping.
The blue racer is a typical colubrine snake of slender build, with
large eyes, and vision plays an important role in finding prey and
detecting enemies. In the adult blue racer the dorsal color is
variable, pale brown or gray, bluish, greenish or slaty. In the
hatchling, however, there is a distinct pattern of a type widespread
among colubrines and also among snakes of other groups--a series of
middorsal blotches on an olive ground color, with alternating rows of
smaller spots on each side. The ventral surface is pale, with dark
speckling. The pattern is sharply defined on the anterior part of the
body, but markings become progressively more obscure posteriorly and
are scarcely discernible on the tail.
The juvenal pattern fades gradually as growth proceeds, and there is
much individual variation in the rate of its loss. Some racers still
retain the juvenal pattern faintly discernible after attainment of
sexual maturity. There are also striking ontogenetic changes in the
proportions of the head, body and tail. The diameter of the eye is
approximately one per cent of the snout-vent length in hatchlings, but
is only a little more than half that relative size in the largest
adults. In the course of allometric growth other parts of the head
also enlarge less rapidly than the body, but more rapidly than the
eye. In hatchlings there is a slight average difference between the
sexes in relative tail length, with males' tails the longer. Relative
tail length increases slightly in both sexes up to the time of sexual
maturity, and then decreases slightly with advancing age.
Racers in northeastern Kansas spend nearly half the year in
hibernation, with average recorded emergence date April 16, and
average date of retirement into hibernation November 8. Hibernacula
are usually in crevices in hilltop limestone outcrops with south
exposures. Winter temperatures within the hibernacula are usually well
within the range 0 degrees to 10 degrees Centigrade. Spring emergence
has been recorded at an air temperature of only 12.5 degrees
Centigrade. Racers bask in sunshine frequently even in warm weather,
and the temperature preferendum is several degrees higher than in most
other kinds of snakes. Bodily temperatures obtained from blue racers
that were fully active, either under natural conditions or in a large
outdoor enclosure, were concentrated in the neighborhood of 34 and 35
degrees Centigrade. For short periods racers can survive temperatures
up to 45 degrees without damage, but more prolonged exposure to
temperatures of slightly less than 40 degrees can be fatal. In
hibernation, racers can withstand temperatures slightly below
freezing, but they cannot survive being frozen solid.
Blue racers tend to limit their activities to familiar areas or home
ranges; some individuals may live out their entire lives within the
same home range, but others shift from time to time. Average home
ranges of approximately 26 acres for males and 24 acres for females
were calculated. The racers' preference for hibernacula in a habitat
different from that to which summer activities are confined
necessitates spring and fall migrations between the limestone outcrops
where hibernation occurs and the grasslands where the snakes stay in
summer. The average spring or fall migration is approximately a
quarter of a mile, but an individual racer does not consistently
return to the same hibernaculum. Many racers were recorded to have
made movements of 2000 to nearly 4000 feet, involving shifts in home
range, but some later shifted back to their original areas. Some may
have made even longer shifts but their movements would not have been
recorded since they would have gotten beyond the limits of the study
area.
Blue racers hunt by various methods, often by coursing through dense
vegetation in active search in which vision is of primary importance
in locating the prey. Almost any small animal that moves nearby may be
overtaken and caught with a sudden dash. From analysis of scats and
prey from stomachs, a total of 1357 food items of more than 50 species
was compiled. Favorite prey species were the cricket (_Gryllus
assimilis_), grasshoppers (_Arphia simplex_, _Melanoplus
femur-rubrum_, _M. bivittatus_, _M. differentialis_), camel crickets
(_Ceuthophilus_ sp.), katydid (_Neoconocephalus robustus_), vole
(_Microtus ochrogaster_), white-footed mouse (_Peromyscus_ sp.),
racerunner, (_Cnemidophorus sexlineatus_), and leopard frog (_Rana
pipiens_). The insects taken greatly outnumbered the vertebrates, but
the vertebrates made up most of the actual bulk of prey eaten.
Crickets, grasshoppers, and katydids comprised most of the insect
prey. Beetles, moths and cicadas were rarely taken. Vertebrate prey
included miscellaneous small snakes (some of them juvenal racers),
mammals, and birds. Seasonal change in the composition of the food is
slight, but vertebrates figure more prominently in early summer, and
insects comprise increasing percentages later in the season.
Composition of the food differs according to size of the snake;
gryllid and ceuthophilid crickets are best represented in the food of
juveniles whereas small mammals, and grasshoppers of the genus
_Melanoplus_ are best represented in the food of large adults.
The breeding season is mainly in May. Mating is promiscuous and two or
more males may court the same female simultaneously. A courting male
lies on or alongside a receptive female, with spasmodic rippling
abdominal movements, and with his vent adpressed to hers. At intervals
in the courtship period the female moves swiftly for a few feet or a
few yards shifting to a new spot, and during her activity the male
strives to maintain contact with her. From time to time the male
leaves the female briefly and courses rapidly around her in a devious
route. Courtship is consummated when the female raises her tail in
acceptance of the male and intromission is effected. During coitus,
which lasts for periods of minutes, the female moves forward slowly,
dragging the passive male, tail-first behind her.
Ovulation normally is in late May. Eggs from 29 to 39 millimeters in
length and 14 to 21 millimeters in breadth are laid, from mid-June to
early August, usually in tunnels of fossorial mammals such as voles or
moles, at depths of five to 12 inches. Clutches of the blue racer
average 11.8 eggs but the number is correlated with age and size of
females; two-year-olds average only 9.2 eggs, whereas those females
that are six years old or more average 15.7 eggs. Also, there is
geographic variation in size of clutch, from only 5.8 eggs in _C. c.
mormon_ of the West Coast to 16.8 eggs in _C. c. constrictor_ of the
northeastern states. In each breeding season some females of adult
size do not produce clutches. Only about 13 per cent of the
two-year-olds in a small sample were fecund, but the ratio increased
to 80 per cent in old adults. Incubation averages 51 (43 to 63) days.
Hatchlings usually make several longitudinal slits in the eggshell
with the egg tooth before emerging, and often require a day or more to
emerge after the first slit is made. Hatchlings average 10-3/4 inches
and 4.16 grams. By late October when these young are ready to enter
hibernation, they have grown to 16-3/4 inches and 12.3 grams. Typical
October lengths (overall) in inches for males and females,
respectively, after successive seasons of growth, are as follows:
yearlings, 27-3/4 and 29; two-year-olds, 34-1/4 and 37-1/4;
three-year-olds, 37-3/4 and 41-3/4; four-year-olds, 40 and 44-3/4;
five-year-olds, 41-1/2 and 46-1/4; six-year-olds, 42-1/4 and 48-1/4;
seven-year-olds, 43-3/4 and 50; eight-year-olds, 44 and 51-1/4.
Judging from trends in the small samples available, sex ratio in
hatchlings is approximately 1:1. In the summer trapping of blue
racers, males are caught in larger numbers than females, but seemingly
this is because of their greater activity. In fall along the limestone
outcrops where the racers hibernate females were caught in slightly
greater numbers than males among the young adults, and made up a
little more than 60 per cent of the old adults. Presumably the males
are eliminated more rapidly, because of their greater activity, their
smaller size, or a combination of both factors. The composition by age
groups of the adult racers captured was as follows: two-year-olds,
41.5 per cent; three-year-olds, 17.8 per cent; four-year-olds, 12.6
per cent; five-year-olds, 9.5 per cent; six-year-olds, 6.1 per cent;
seven-year-olds, 4.3 per cent; eight-year-olds, 2.7 per cent;
nine-year-olds, 2.4 per cent; ten-year-olds, 1.2 per cent; more than
ten years old, 1.9 per cent.
Attempts to census blue racers on the study plots, from the
capture-recapture ratios, yielded highly variable figures for
different areas and even for the same area at different times.
Variability is believed to result mostly from the small sizes of the
samples, none of which is large enough to yield a census figure that
is statistically reliable. Combined samples yielded figures indicating
populations of one to three adults per acre in early summer in areas
of favorable habitat. To represent the entire population in late
summer--the time of its annual maximum--these figures would need to be
approximately tripled.
The blue racer depends mostly on speed to escape its enemies. In
escaping it often takes advantage of a downhill slope to increase its
speed. A racer startled at close range often sets out with a violent
thrashing that attracts attention to a given spot, then glides away so
silently and rapidly that its course is not detected. The snake may
circle back and approach the scene of disturbance slowly and
stealthily, from the direction opposite to that taken in departing.
Often a racer seeks concealment by climbing into a bush or tree, and
occasionally escape is effected by swimming. A racer that is caught or
cornered usually makes a spirited defense by striking and biting. An
alternative reaction, seen most typically when the snake is
handicapped by injury or by low temperature, is to coil with the head
concealed, and, with writhing movements, to smear the surface of the
body with musk discharged from glands in the base of the tail.
Many natural enemies prey upon the racer, but in the present study the
majority of records pertained to the red-tailed hawk. The broad-winged
hawk, marsh hawk, red-shouldered hawk, sparrow hawk, and barn owl also
are among the raptors that feed on this kind of snake. Among mammals
the striped skunk is the only species definitely recorded to prey on
the racer, feeding on the eggs as well as upon the young and adults.
The common king snake, prairie king snake, timber rattlesnake,
copperhead, and even the slender glass lizard have been recorded to
prey on the blue racer, but probably all are of minor importance as
natural enemies. Shrews (_Blarina_, _Cryptotis_) and mice
(_Peromyscus_, _Reithrodontomys_) have sometimes killed and eaten
racers confined in traps, and under natural conditions they possibly
prey upon snakes that are immobilized when torpid from cold, in their
hibernacula and temporary shelters. Chiggers are the most common
ectoparasites of the racers. Four species of the chigger genus
_Trombicula_ have been recorded on racers from the Reservation. The
racer is an important host of the common pest chigger, _Trombicula
alfreddugèsi_, which often attacks humans. Most adult racers on the
Reservation and nearby areas carry the fluke, _Neorenifer
lateriporus_. In spring these flukes are conspicuous in the mouths of
the racers, but in late summer they are not in evidence.
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1960. Autecology of the copperhead. Univ. Kansas Publ. Mus. Nat.
Hist., 13(4):85-288.
Fitch, H. S. and Packard, R. L.
1955. The coyote on a natural area in northeastern Kansas.
Trans. Kansas Acad. Sci., 58:211-221.
Fitch, H. S. and Sandidge, L. L.
1953. Ecology of the opossum on a natural area in northeastern
Kansas. Univ. Kansas Publ. Mus. Nat. Hist., 7(2):305-338.
Force, E. R.
1930. The amphibians and reptiles of Tulsa County, Oklahoma, and
vicinity. Copeia, 1930(2):25-39.
Fouquette, M. J. and Lindsay, H. L., Jr.
1955. An ecological survey of reptiles in parts of northwestern
Texas. The Texas Jour. Sci., 7(4):402-421.
Gloyd, H. K.
1928. The amphibians and reptiles of Franklin County, Kansas.
Trans. Kansas Acad. Sci., 31:115-141.
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Grinnell, J., Dixon, J., and Linsdale, J. M.
1930. Vertebrate natural history of a section of northern
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Guidry, E. V.
1953. Herpetological notes from southeastern Texas.
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Hamilton, W. J., Jr., and Pollack, J. A.
1956. The food of some colubrid snakes from Fort Benning,
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Harwood, P. D.
1933. The helminths parasitic in the Amphibia and Reptilia of
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1936. The amphibians and reptiles of Mammoth Cave National Park
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Hudson, G. E.
1942. The amphibians and reptiles of Nebraska. Nebraska
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Hudson, R. G.
1949. A record length milk snake. Herpetologica, 5:47.
Hurter, J. H.
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20:59-274.
Inger, F. and Clark, P. J.
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1939. The analysis of an animal population. Jour. An. Ecology,
8:238-246.
King, W.
1939. A survey of the herpetology of Great Smoky Mountain
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Klimstra, W. D.
1959. Food of the racer, _Coluber constrictor_, in southern
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Langbartel, D. A.
1947. Snakes collected at Camp Eastman, Hancock County,
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1949. Notes on the young of the blue racer, _Coluber constrictor
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1954. The herpetofauna of Lafayette, Terrebonne, and Vermilion
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1927. Amphibians and reptiles of Doniphan County, Kansas.
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1940. On some reptilian cestodes of the genus Oochoristica
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1932. Some account of the amphibians and reptiles of British
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1956. The chigger mites of Kansas (Acarina, Trombiculidae).
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1944. Notes on amphibians and reptiles from the central United
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Martin, E. P.
1956. A population study of the prairie vole (_Microtus
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Maslin, T. P.
1959. An annotated check list of the amphibians and reptiles of
Colorado. Univ. Colorado Studies, Biol. Series, No. 6, 98
pp.
McCauley, R. H.
1945. The reptiles of Maryland and the District of Columbia.
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1944. Introduction to the study of reptiles in Indiana. Amer.
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Mossiman, J. E. and Rabb, G. B.
1952. The herpetology of the Tiber River area, Montana. Copeia,
1952(1):23-27.
Mulaik, S. and Mulaik, D.
1942. A neglected species of Coluber. Copeia, 1942:13-15.
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1948. Comparative sizes of two female blue racers and their
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Herpetologica, 6:124.
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1948. Hibernation of amphibians and reptiles in Richmond County,
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1941. The trematode parasites from a collection of amphibians
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1942. Reptiles and amphibians of Cumberland County, Illinois.
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1935. The reptiles of China. Amer. Mus. Nat. Hist., Nat. Hist.
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1960. Herpetological survey of the pine hills area of southern
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1959. Lung flukes of _Thamnophis_ and _Coluber_ in Kansas.
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1937. Ecological observations on amphibians and reptiles
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1931. A descriptive catalog of the reptiles of Utah. Bull. Univ.
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xviii + 564 pp.
_Transmitted June 3, 1963._
[]
29-7864
UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY
Institutional libraries interested in publications exchange may obtain
this series by addressing the Exchange Librarian, University of Kansas
Library, Lawrence, Kansas. Copies for individuals, persons working in
a particular field of study, may be obtained by addressing instead the
Museum of Natural History, University of Kansas, Lawrence, Kansas.
There is no provision for sale of this series by the University
Library, which meets institutional requests, or by the Museum of
Natural History, which meets the requests of individuals.
Nevertheless, when individuals request copies from the Museum, 25
cents should be included, for each separate number that is 100 pages
or more in length, for the purpose of defraying the costs of wrapping
and mailing.
* An asterisk designates those numbers of which the Museum's supply
(not the Library's supply) is exhausted. Numbers published to date, in
this series, are as follows:
Vol. 1. Nos. 1-26 and index. Pp. 1-638, 1946-1950.
*Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest.
Pp. 1-444, 140 figures in text. April 9, 1948.
Vol. 3. *1. The avifauna of Micronesia, its origin, evolution,
and distribution. By Rollin H. Baker. Pp. 1-359,
16 figures in text. June 12, 1951.
*2. A quantitative study of the nocturnal migration of
birds. By George H. Lowery, Jr. Pp. 361-472,
47 figures in text. June 29, 1951.
3. Phylogeny of the waxwings and allied birds. By M.
Dale Arvey. Pp. 473-530, 49 figures in text,
13 tables. October 10, 1951.
*4. Birds from the state of Veracruz, Mexico. By George
H. Lowery, Jr., and Walter W. Dalquest. Pp. 531-649,
7 figures in text, 2 tables. October 10, 1951.
Index. Pp. 651-681.
*Vol. 4. (Complete) American weasels. By E. Raymond Hall.
Pp. 1-466, 41 plates, 31 figures in text.
December 27, 1951.
Vol. 5. Nos. 1-37 and index. Pp. 1-676, 1951-1953.
*Vol. 6. (Complete) Mammals of Utah, _taxonomy and distribution_.
By Stephen D. Durrant. Pp. 1-549, 91 figures in text,
30 tables. August 10, 1952.
Vol. 7. Nos. 1-15 and index. Pp. 1-651, 1952-1955.
Vol. 8. Nos. 1-10 and index. Pp. 1-675, 1954-1956.
Vol. 9. *1. Speciation of the wandering shrew. By James S.
Findley. Pp. 1-68, 18 figures in text.
December 10, 1955.
2. Additional records and extension of ranges of mammals
from Utah. By Stephen D. Durrant, M. Raymond Lee, and
Richard M. Hansen. Pp. 69-80. December 10, 1955.
3. A new long-eared myotis (Myotis evotis) from
northeastern Mexico. By Rollin H. Baker and Howard J.
Stains. Pp. 81-84. December 10, 1955.
4. Subspeciation in the meadow mouse, Microtus
pennsylvanicus, in Wyoming. By Sydney Anderson.
Pp. 85-104, 2 figures in text. May 10, 1956.
5. The condylarth genus Ellipsodon. By Robert W. Wilson.
Pp. 105-116, 6 figures in text. May 19, 1956.
6. Additional remains of the multituberculate genus
Eucosmodon. By Robert W. Wilson. Pp. 117-123,
10 figures in text. May 19, 1956.
7. Mammals of Coahulia, Mexico. By Rollin H. Baker.
Pp. 125-335, 75 figures in text. June 15, 1956.
8. Comments on the taxonomic status of Apodemus
peninsulae, with description of a new subspecies
from North China. By J. Knox Jones, Jr. Pp. 337-346,
1 figure in text, 1 table. August 15, 1956.
9. Extensions of known ranges of Mexican bats. By
Sydney Anderson. Pp. 347-351. August 15, 1956.
10. A new bat (Genus Leptonycteris) from Coahulia. By
Howard J. Stains. Pp. 353-356. January 21, 1957.
11. A new species of pocket gopher (Genus Pappogeomys)
from Jalisco, Mexico. By Robert J. Russell.
Pp. 357-361. January 21, 1957.
12. Geographic variation in the pocket gopher, Thomomys
bottae, in Colorado. By Phillip M. Youngman.
Pp. 363-387, 7 figures in text. February 21, 1958.
13. New bog lemming (genus Synaptomys) from Nebraska.
By J. Knox Jones, Jr. Pp. 385-388. May 12, 1958.
14. Pleistocene bats from San Josecito Cave, Nuevo León,
México. By J. Knox Jones, Jr. Pp. 389-396.
December 19, 1958.
15. New subspecies of the rodent Baiomys from Central
America. By Robert L. Packard. Pp. 397-404.
December 19, 1958.
16. Mammals of the Grand Mesa, Colorado. By Sydney
Anderson. Pp. 405-414, 1 figure in text,
May 20, 1959.
17. Distribution, variation, and relationships of the
montane vole, Microtus montanus. By Sydney Anderson.
Pp. 415-511, 12 figures in text, 2 tables.
August 1, 1959.
18. Conspecificity of two pocket mice, Perognathus
goldmani and P. artus. By E. Raymond Hall and Marilyn
Bailey Ogilvie. Pp. 513-518, 1 map. January 14, 1960.
19. Records of harvest mice, Reithrodontomys, from
Central America, with description of a new subspecies
from Nicaragua. By Sydney Anderson and J. Knox Jones,
Jr. Pp. 519-529. January 14, 1960.
20. Small carnivores from San Josecito Cave (Pleistocene),
Nuevo León, México. By E. Raymond Hall. Pp. 531-538,
1 figure in text. January 14, 1960.
21. Pleistocene pocket gophers from San Josecito Cave,
Nuevo León, México. By Robert J. Russell.
Pp. 539-548,1 figure in text. January 14, 1960.
22. Review of the insectivores of Korea. By J. Knox
Jones, Jr., and David H. Johnson. Pp. 549-578.
February 23, 1960.
23. Speciation and evolution of the pygmy mice, genus
Baimoys. By Robert L. Packard. Pp. 579-670, 4 plates,
12 figures in text. June 16, 1960.
Index. Pp. 671-690
Vol. 10. 1. Studies of birds killed in nocturnal migration. By
Harrison B. Tordoff and Robert M. Mengel. Pp. 1-44,
6 figures in text, 2 tables. September 12, 1956.
2. Comparative breeding behavior of Ammospiza caudacuta
and A. maritima. By Glen E. Woolfenden. Pp. 45-75,
6 plates, 1 figure. December 20, 1956.
3. The forest habitat of the University of Kansas
Natural History Reservation. By Henry S. Fitch and
Ronald R. McGregor. Pp. 77-127, 2 plates, 7 figures
in text, 4 tables. December 31, 1956.
4. Aspects of reproduction and development in the
prairie vole (Microtus ochrogaster). By Henry S.
Fitch. Pp. 129-161, 8 figures in text, 4 tables.
December 19, 1957.
5. Birds found on the Arctic slope of northern Alaska.
By James W. Bee. Pp. 163-211, plates 9-10, 1 figure
in text. March 12, 1958.
*6. The wood rats of Colorado: distribution and ecology.
By Robert B. Finley, Jr. Pp. 213-552, 34 plates,
8 figures in text, 35 tables. November 7, 1958.
7. Home ranges and movements of the eastern cottontail
in Kansas. By Donald W. Janes. Pp. 553-572, 4 plates,
3 figures in text. May 4, 1959.
8. Natural history of the salamander, Aneides hardyi.
By Richard F. Johnston and Gerhard A. Schad.
Pp. 573-585. October 8, 1959.
9. A new subspecies of lizard, Cnemidophorus sacki,
from Michoacán, México. By William E. Duellman.
Pp. 587-598, 2 figures in text. May 2, 1960.
10. A taxonomic study of the middle American snake,
Pituophis deppei. By William E. Duellman.
Pp. 599-610, 1 plate, 1 figure in text. May 2, 1960.
Index. Pp. 611-626.
Vol. 11. Nos. 1-10 and index. Pp. 1-703, 1958-1960.
Vol. 12. 1. Functional morphology of three bats: Sumops, Myotis,
Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates,
24 figures in text. July 8, 1959.
*2. The ancestry of modern Amphibia: a review of the
evidence. By Theodore H. Eaton, Jr. Pp. 155-180,
10 figures in text. July 10, 1959.
3. The baculum in microtine rodents. By Sydney Anderson.
Pp. 181-216, 49 figures in text. February 19, 1960.
*4. A new order of fishlike Amphibia from the
Pennsylvanian of Kansas. By Theodore H. Eaton, Jr.,
and Peggy Lou Stewart. Pp. 217-240, 12 figures in
text. May 2, 1960.
5. Natural history of the bell vireo. By Jon C. Barlow.
Pp. 241-296, 6 figures in text. March 7, 1962.
6. Two new pelycosaurs from the lower Permian of
Oklahoma. By Richard C. Fox. Pp. 297-307, 6 figures
in text. May 21, 1962.
7. Vertebrates from the barrier island of Tamaulipas,
México. By Robert K. Selander, Richard F. Johnston,
B. J. Wilks, and Gerald G. Raun. Pp. 309-345,
pls. 5-8. June 18, 1962.
8. Teeth of Edestid sharks. By Theodore H. Eaton, Jr.
Pp. 347-362, 10 figures in text. October 1, 1962.
9. Variation in the muscles and nerves of the leg in
two genera of grouse (Tympanuchus and Pedioecetes).
By E. Bruce Holmes. Pp. 363-474, 20 figs. October
25, 1963.
10. A new genus of Pennsylvanian Fish (Crossopterygii,
Coelacanthiformes) from Kansas. By Joan Echols.
Pp. 475-501, 7 figures. October 25, 1963.
11. Observations on the Mississippi Kite in southwestern
Kansas. By Henry S. Fitch. Pp. 503-519. October 25, 1963.
12. Jaw musculature of the Mourning and White-winged doves.
By Robert L. Merz. Pp. 521-551, 22 figures. October 25,
1963.
More numbers will appear in volume 12.
Vol. 13. 1. Five natural hybrid combinations in minnows
(Cyprinidae). By Frank B. Cross and W. L. Minckley.
Pp. 1-18. June 1, 1960.
2. A distributional study of the amphibians of the
Isthmus of Tehuantepec, México. By William E.
Duellman. Pp. 19-72, pls. 1-8, 3 figures in text.
August 16, 1960.
3. A new subspecies of the slider turtle (Pseudemys
scripta) from Coahulia, México. By John M. Legler.
Pp. 73-84, pls. 9-12, 3 figures in text.
August 16, 1960.
4. Autecology of the copperhead. By Henry S. Fitch.
Pp. 85-288, pls. 13-20, 26 figures in text.
November 30, 1960.
5. Occurrence of the garter snake, Thamnophis sirtalis,
in the Great Plains and Rocky Mountains. By Henry S.
Fitch and T. Paul Maslin. Pp. 289-308, 4 figures in
text. February 10, 1961.
6. Fishes of the Wakarusa river in Kansas. By James E.
Deacon and Artie L. Metcalf. Pp. 309-322, 1 figure
in text. February 10, 1961.
7. Geographic variation in the North American cyprinid
fish, Hybopsis gracilis. By Leonard J. Olund and
Frank B. Cross. Pp. 323-348, pls. 21-24, 2 figures
in text. February 10, 1961.
8. Descriptions of two species of frogs, genus
Ptychohyla; studies of American hylid frogs, V.
By William E. Duellman. Pp. 349-357, pl. 25,
2 figures in text. April 27, 1961.
9. Fish populations, following a drought, in the Neosho
and Marais des Cygnes rivers of Kansas. By James
Everett Deacon. Pp. 359-427, pls. 26-30, 3 figs.
August 11, 1961.
10. Recent soft-shelled turtles of North America (family
Trionychidae). By Robert G. Webb. Pp. 429-611,
pls. 31-54, 24 figures in text, February 16, 1962.
Index. Pp. 613-624.
Vol. 14. 1. Neotropical bats from western México. By Sydney
Anderson. Pp. 1-8. October 24, 1960.
2. Geographic variation in the harvest mouse.
Reithrodontomys megalotis, on the central Great
Plains and in adjacent regions. By J. Knox Jones, Jr.,
and B. Mursaloglu. Pp. 9-27, 1 figure in text.
July 24, 1961.
3. Mammals of Mesa Verde National Park, Colorado.
By Sydney Anderson. Pp. 29-67, pls. 1 and 2,
3 figures in text. July 24, 1961.
4. A new subspecies of the black myotis (bat) from
eastern Mexico. By E. Raymond Hall and Ticul Alvarez.
Pp. 69-72, 1 figure in text. December 29, 1961.
5. North American yellow bats, "Dasypterus," and a list
of the named kinds of the genus Lasiurus Gray.
By E. Raymond Hall and J. Knox Jones, Jr. Pp. 73-98,
4 figures in text. December 29, 1961.
6. Natural history of the brush mouse (Peromyscus
boylii) in Kansas with description of a new
subspecies. By Charles A. Long. Pp. 99-111, 1 figure
in text. December 29, 1961.
7. Taxonomic status of some mice of the Peromyscus
boylii group in eastern Mexico, with description of
a new subspecies. By Ticul Alvarez. Pp. 113-120,
1 figure in text. December 29, 1961.
8. A new subspecies of ground squirrel (Spermophilus
spilosoma) from Tamaulipas, Mexico. By Ticul Alvarez.
Pp. 121-124. March 7, 1962.
9. Taxonomic status of the free-tailed bat, Tadarida
yucatanica Miller. By J. Knox Jones, Jr., and Ticul
Alvarez. Pp. 125-133, 1 figure in text.
March 7, 1962.
10. A new doglike carnivore, genus Cynaretus, from the
Clarendonian Pliocene, of Texas. By E. Raymond Hall
and Walter W. Dalquest. Pp. 135-138, 2 figures in
text. April 30, 1962.
11. A new subspecies of wood rat (Neotoma) from
northeastern Mexico. By Ticul Alvarez. Pp. 139-143.
April 30, 1962.
12. Noteworthy mammals from Sinaloa, Mexico. By J. Knox
Jones, Jr., Ticul Alvarez, and M. Raymond Lee.
Pp. 145-159, 1 figure in text. May 18, 1962.
13. A new bat (Myotis) from Mexico. By E. Raymond Hall.
Pp. 161-164, 1 figure in text. May 21, 1962.
14. The mammals of Veracruz. By E. Raymond Hall and
Walter W. Dalquest. Pp. 165-362, 2 figures.
May 20, 1963.
15. The recent mammals of Tamaulipas, México. By Ticul
Alvarez. Pp. 363-473, 5 figures in text.
May 20, 1963.
More numbers will appear in volume 14.
Vol. 15. 1. The amphibians and reptiles of Michoacán, México.
By William E. Duellman. Pp. 1-148, pls. 1-6,
11 figures in text. December 20, 1961.
2. Some reptiles and amphibians from Korea. By Robert
G. Webb, J. Knox Jones, Jr., and George W. Byers.
Pp. 149-173. January 31, 1962.
3. A new species of frog (Genus Tomodactylus) from
western México. By Robert G. Webb. Pp. 175-181,
1 figure in text. March 7, 1962.
4. Type specimens of amphibians and reptiles in the
Museum of Natural History, the University of Kansas.
By William E. Duellman and Barbara Berg. Pp. 183-204.
October 26, 1962.
5. Amphibians and Reptiles of the Rainforests of
Southern El Petén, Guatemala. By William E. Duellman.
Pp. 205-249, pls. 7-10, 6 figures in text.
October 4, 1963.
6. A revision of snakes of the genus Conophis (Family
Colubridae, from Middle America). By John Wellman.
Pp. 251-295, 9 figures in text. October 4, 1963.
7. A review of the Middle American tree frogs of the
genus Ptychohyla. By William E. Duellman.
Pp. 297-349, pls. 11-18, 7 figures in text.
October 18, 1963.
8. Natural history of the racer, Coluber constrictor.
By Henry S. Fitch. Pp. 351-468, pls. 19-22,
20 figures. December 30, 1963.
More numbers will appear in volume 15.
Transcriber's Notes
Where tables or images split them, the text was moved to rejoin
paragraphs. The List of Publications before the article was moved
down to rejoin the portion after the end of the article.
Table 6 re-arranged due to use of vertically printed text. Tables 18
and 19 rearranged due to width considerations in text version.
Page 451 may have a typo "...wide range of error arising from
insufficiently =small= samples..." should probably have been
"...=large= samples..." (emphasis added here). This was left as is.
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