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Title: Field Study of Kansas Ant-Eating Frog
Author: Henry S. Fitch
Release Date: August 29, 2010 [EBook #33574]
Language: English
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* * * * *
UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY
Volume 8, No. 4, pp. 275-306, 9 figs. in text
February 10, 1956
A Field Study
of the Kansas Ant-Eating Frog,
Gastrophryne olivacea
BY
HENRY S. FITCH
UNIVERSITY OF KANSAS
LAWRENCE
1956
UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
Robert W. Wilson
Volume 8, No. 4, pp. 275-306, 9 figs. in text
Published February 10, 1956
UNIVERSITY OF KANSAS
Lawrence, Kansas
PRINTED BY
FERD VOILAND. JR., STATE PRINTER
TOPEKA, KANSAS
1956
25-7819
A FIELD STUDY OF THE KANSAS ANT-EATING FROG, GASTROPHRYNE OLIVACEA
By
Henry S. Fitch
INTRODUCTION
The ant-eating frog is one of the smallest species of vertebrates on the
University of Kansas Natural History Reservation, but individually it is
one of the most numerous. The species is important in the over-all
ecology; its biomass often exceeds that of larger species of
vertebrates. Because of secretive and subterranean habits, however, its
abundance and effects on community associates are largely obscured.
The Reservation, where my field study was made, is the most northeastern
section in Douglas County, Kansas, and is approximately 5½ miles north
and 2½ miles east of the University campus at Lawrence. The locality
represents one of the northernmost occurrences of the species, genus,
and family. The family Microhylidae is a large one, and most of its
representatives are specialized for a subterranean existence and a diet
of termites or ants. The many subfamilies of microhylids all have
distributions centering in the regions bordering the Indian Ocean, from
South Africa and Madagascar to the East Indies, New Guinea, and
Australia (Parker, 1934). Only one subfamily, the Microhylinae, is
represented in the New World, where it has some 17 genera (de Carvalho,
1954) nearly all of which are tropical. _G. olivacea_, extending north
into extreme southern Nebraska (Loomis, 1945: 211), ranges farther north
than any other American species. In the Old World only _Kaloula
borealis_ has a comparable northward distribution. Occurring in the
vicinity of Peiping (Pope, 1931: 587), it reaches approximately the same
latitude as does _Gastrophryne_ in Nebraska. The great majority of
microhylid genera and species are confined to the tropics.
Nearly all ant-eating frogs seen on the Reservation have been caught and
examined and individually marked. By November 1, 1954, 1215 individuals
had been recorded with a total of 1472 captures. In the summer of 1950,
Richard Freiburg studied this frog on the Reservation and his findings
(1951) led to a better understanding of its natural history. The
numbers of frogs studied by him however, were relatively small and the
field work was limited to the one summer. The data now at hand,
representing six consecutive years, 1949 through 1954, serve to
supplement those obtained by Freiburg, corroborating and extending his
conclusions in most instances, and also indicating that certain of his
tentative conclusions need to be revised.
While the present report was in preparation, Anderson (1954) published
an excellent account of the ecology of the eastern species _G.
carolinensis_ in southern Louisiana. Anderson's findings concerning this
closely related species in a much different environment have been
especially valuable as a basis for comparison. The two species are
basically similar in their habits and ecology but many minor differences
are indicated. Some of these differences result from the differing
environments where Anderson's study and my own were made and others
certainly result from innate genetic differences between the species.
The frog with which this report is concerned is the _Microhyla
carolinensis olivacea_ of the check list (Schmidt, 1953: 77) and recent
authors. De Carvalho (1954: 12) resurrected the generic name,
_Gastrophryne_, for the American species formerly included in
_Microhyla_, and presented seemingly valid morphological evidence for
this plausible generic separation.
_G. olivacea_ is obviously closely related to _G. carolinensis_; the
differences are not greater than those to be expected between well
marked subspecies. Nevertheless, in eastern Oklahoma and eastern Texas,
where the ranges meet, the two kinds have been found to maintain their
distinctness, differing in coloration, behavior, calls, and time of
breeding. Hecht and Matalas (1946: 2) found seeming intergrades from the
area of overlapping in eastern Texas, but some specimens from this same
area were typical of each form. Their study was limited to preserved
material, in which some characters probably were obscured. More field
work throughout the zone of contact is needed. The evidence of
intergradation obtained so far seems to be somewhat equivocal.
Besides _G. olivacea_ and typical _G. carolinensis_ there are several
named forms in the genus, including some of doubtful status. The name
_mazatlanensis_ has been applied to a southwestern population, which
seems to be a well marked subspecies of _olivacea_, but as yet
_mazatlanensis_ has been collected at few localities and the evidence of
intergradation is meager. The names _areolata_ and _texensis_ have been
applied to populations in Texas. Hecht and Matalas (1946: 3) consider
_areolata_ to be a synonym of _olivacea_, applied to a population
showing intergradation with _carolinensis_, but Wright and Wright (1949:
568) consider _areolata_ to be a distinct subspecies. _G. texensis_
generally has been considered to be a synonym of _olivacea_. Other
species of the genus include the tropical _G. usta_, _G. elegans_ and
_G. pictiventris_.
Of the vernacular names hitherto applied to _G. olivacea_ none seems
appropriate; I propose to call the species the Kansas ant-eating frog
because of its range extending over most of the state, and because of
its specialized food habits. The type locality, originally stated to be
"Kansas and Nebraska" (Hallowell, 1856: 252) has been restricted to Fort
Riley, Kansas (Smith and Taylor, 1950: 358). Members of the genus have
most often been referred to as toads rather than frogs because of their
more toadlike appearance and habits. However, this family belongs to the
firmisternial or froglike division of the Salientia and the terms "frog"
and "toad," originally applied to _Rana_ and _Bufo_ respectively, have
been extended to include assemblages of related genera or families.
Members of the genus and family usually have been called
"narrow-mouthed" toads from the old generic name _Engystoma_, a synonym
of _Gastrophryne_. _G. olivacea_ usually has been referred to as the
Texas narrow-mouthed toad, or western narrow-mouthed toad. The latter
name is inappropriate because the geographic range is between that of a
more western representative (_mazatlanensis_) and a more eastern one
(_carolinensis_). The names _texensis_, _areolata_ and _carolinensis_
have all been applied to populations in Texas, and it is questionable
whether typical _olivacea_ even extends into Texas.
HABITAT
In the northeastern part of Kansas at least, rocky slopes in open woods
seem to provide optimum habitat conditions. This type of habitat has
been described by several earlier workers in this same area, Dice (1923:
46), Smith (1934: 503) and Freiburg (1951: 375). Smith (1950: 113)
stated that in Kansas this frog is found in wooded areas, and that rocks
are the usual cover, but he mentioned that outside of Kansas it is often
found in mesquite flats that are devoid of rocks. Freiburg's field work
was done almost entirely on the Reservation and was concentrated in
"Skink Woods" and vicinity, where much of my own field work, both before
and afterward, was concentrated. On the Reservation and in nearby
counties of Kansas, the habitat preferences of the ant-eating frog and
the five-lined skink largely coincide. In an account of the five-lined
skink on the Reservation, I have described several study areas in some
detail (Fitch, 1954: 37-41). It was on these same study areas (Quarry,
Skink Woods, Rat Woods) that most of the frogs were obtained.
Although _G. olivacea_ thrives in an open-woodland habitat in this part
of its range, it seems to be essentially a grassland species, and it
occurs throughout approximately the southern half of the Great Plains
region. Bragg (1943: 76) emphasized that in Oklahoma it is widely
distributed over the state, occupying a variety of habitats, with little
ecological restriction. Bragg noted, however, that the species is
rarely, if ever, found on extensive river flood plains. On various
occasions I have heard _Gastrophryne_ choruses in a slough two miles
south of the Reservation. This slough is in the Kaw River flood plain
and is two miles from the bluffs where the habitat of rocky wooded
slopes begins that has been considered typical of the species in
northeastern Kansas. It seems that the frogs using this slough are not
drawn from the populations living on the bluffs as Mud Creek, a Kaw
River tributary, intervenes. The creek channel at times of heavy
rainfall, carries a torrent of swirling water which might present a
barrier to migrating frogs as they are not strong swimmers. The frogs
could easily find suitable breeding places much nearer to the bluffs.
Those using the slough are almost certainly permanent inhabitants of the
river flood plain. The area in the neighborhood of the slough, where the
frogs probably live, include fields of alfalfa and other cultivated
crops, weedy fallow fields, and the marshy margins of the slough. In
these situations burrows of rodents, notably those of the pocket gopher
(_Geomys bursarius_), would provide subterranean shelter for the frogs,
which are not efficient diggers.
The frogs may live in many situations such as this where they have been
overlooked. In the absence of flat rocks providing hiding places at the
soil surface, the frogs would rarely be found by a collector. The volume
and carrying quality of the voice are much less than in other common
anurans. Large breeding choruses might be overlooked unless the observer
happened to come within a few yards of them. Most of the recorded
habitats and localities of occurrence may be those where the frog
happens to be most in evidence to human observers, rather than those
that are limiting to it or even typical of it.
On September 20, 1954, after heavy rains, juveniles dispersing from
breeding ponds were in a wide variety of situations, including most of
the habitat types represented on the Reservation. Along a small dry
gully in an eroded field formerly cultivated, and reverted to tall
grass prairie (big bluestem, little bluestem, switch grass, Indian
grass), the frogs were numerous. Many of them were flushed by my
footsteps from cracks in the soil along the gully banks. In reaching
this area the frogs had moved up a wooded slope from the pond, crossed
the limestone outcrop area at the hilltop edge, and wandered away from
the woods and rocks, out into the prairie habitat. In this prairie
habitat there were no rocks providing hiding places at the soil surface,
but burrows of the vole (_Microtus ochrogaster_) and other small rodents
provided an abundance of subterranean shelter. In the summer of 1955 the
frogs were seen frequently in this same area, especially when the soil
was wet from recent rain. When the surface of the soil was dry, none
could be found and presumably all stayed in deep cracks and burrows.
Anderson (1954: 17) indicated that _G. carolinensis_ in Louisiana
likewise occurs in diverse habitats, being sufficiently adaptable to
satisfy its basic requirements in various ways.
BEHAVIOR
Ordinarily the ant-eating frog stays beneath the soil surface, in cracks
or holes or beneath rocks. Probably it obtains its food in such
situations, and rarely wanders on the surface. The occasional
individuals found moving about above ground are in most instances
flushed from their shelters by the vibrations of the observer's
footsteps. On numerous occasions I have noticed individuals, startled by
nearby footfalls, dart from cracks or under rocks and scuttle away in
search of other shelter. Such behavior suggests that digging predators
may be important natural enemies. The gait is a combination of running
and short hops that are usually only an inch or two in length. The flat
pointed head seems to be in contact with the ground or very near to it
as the animal moves about rapidly and erratically. The frog has a
proclivity for squeezing into holes and cracks, or beneath objects on
the ground. The burst of activity by one that is startled lasts for only
a few seconds. Then the frog stops abruptly, usually concealed wholly or
in part by some object. Having stopped it tends to rely on concealment
for protection and may allow close approach before it flushes again.
Less frequently, undisturbed individuals have been seen wandering on the
soil surface. Such wandering occurs chiefly at night. Diurnal wandering
may occur in relatively cool weather when night temperatures are too low
for the frogs to be active. Wandering above ground is limited to times
when the soil and vegetation are wet, mainly during heavy rains and
immediately afterward.
Pitfalls made from gallon cans buried in the ground with tops open and
flush with the soil surface were installed in 1949 in several places
along hilltop rock outcrops where the frogs were abundant. The number of
frogs caught from day to day under varying weather-conditions provided
evidence as to the factors controlling surface activity. After nights of
unusually heavy rainfall, a dozen frogs, or even several dozen, might be
found in each of the more productive pitfalls. A few more might be
caught on the following night, and occasional stragglers as long as the
soil remained damp with heavy dew. Activity is greatest on hot summer
nights. Below 20° C. there is little surface activity but individuals
that had body temperatures as low as 16° C. have been found moving
about.
Frogs uncovered in their hiding places beneath flat rocks often remained
motionless depending on concealment for protection, but if further
disturbed, they made off with the running and hopping gait already
described. Although they were not swift, they were elusive because of
their sudden changes of direction and the ease with which they found
shelter. When actually grasped, a frog would struggle only momentarily,
then would become limp with its legs extended. The viscous dermal
secretions copiously produced by a frog being handled made the animal so
slippery that after a few seconds it might slide from the captor's
grasp, and always was quick to escape when such an opportunity was
presented.
TEMPERATURE RELATIONSHIPS
Ant-eating frogs are active over a temperature range of at least 16° C.
to 37.6° C. They tolerate high temperatures that would be lethal to many
other kinds of amphibians, but are more sensitive to low temperatures
than any of the other local species, and as a result their seasonal
schedule resembles that of the larger lizards and snakes more than those
of other local amphibians. The latter become active earlier in the
spring.
Earliest recorded dates when the frogs were found active in the course
of the present study from 1950 to 1955 were in April every year; the
20th, 25th, 24th, 2nd, 25th, and 21st. Latest dates when the frogs were
found in the six years of the study were: October 22, 1949; October 13,
1950; October 7, 1951; August 24, 1952; August 18, 1953; and October 27,
1954 (excluding two late stragglers caught in a pitfall on December 5).
Severe drought caused unseasonably early retirement in 1952 and 1953.
Body temperatures of the frogs were taken with a small mercury
thermometer of the type described by Bogert (1949: 197); the bulb was
used to force open the mouth and was thrust down the gullet into the
stomach. To prevent conduction of heat from the hand, the frog was held
down through several layers of cloth, at the spot where it was
discovered, until the temperature reading could be made. This required
approximately five seconds.
[Illustration: FIG. 1. Temperatures of ant-eating frogs grouped in
one-degree intervals; upper figure is of frogs found active in the open,
and lower is of those found under shelter. The frogs are active over a
temperature range of more than 20 degrees, and show no clear cut
preference within this range.]
Most of the 79 frogs of which temperatures were measured, were found
under shelter, chiefly beneath flat rocks. The rocks most utilized were
in open situations, exposed to sunshine. Most of the frogs were in
contact with the warmed undersurfaces of such rocks. Forty-three of the
frogs, approximately 54.5 percent, were in the eight-degree range
between 24° and 31° C. Probably the preferred temperatures lie within
this range. The highest body temperature recorded, 37.6° C., was in a
frog which "froze" and remained motionless in the sunshine for half a
minute after the rock sheltering it was overturned. Probably its
temperature was several degrees lower while it was sheltered by the
rock. Other unusually high temperatures were recorded in newly
metamorphosed frogs found hiding in piles of decaying vegetation near
the edge of the pond, on hot afternoons of late August. Temperatures
ranged from 17.0° to 30.7° in frogs that were found actually moving
about. Several with relatively low temperatures, 22° to 17°, were
juveniles travelling in rain or mist on cool days. These frogs, having
relatively low temperature, were sluggish in their movements, as
compared with individuals at the upper end of the temperature range.
[Illustration: FIG. 2. Body temperatures and nearby air temperatures for
frogs found under natural conditions. Dots represent frogs found under
shelter; circles represent those found in the open.]
After the first frost each year the frogs usually could not be found,
either in the open or in their usual hiding places beneath rocks. They
probably had retired to deep subterranean hibernation sites. The only
exception was in 1954, when two immature frogs were found together in a
pitfall on the morning of December 5 after a rain of .55 inches ending
many weeks of drought. Air temperature had been little above 10° C. that
night, but had often been below freezing in the preceding five weeks.
Reactions of these same two individuals to low temperatures were tested
in the laboratory. At a body temperature of 11° C. they were extremely
sluggish. They were capable of slow, waddling movements, but were
reluctant to move and tended to crouch motionless. Even when they were
prodded, they usually did not move away, but merely flinched slightly.
At 6° C. they were even more sluggish, and seemed incapable of
locomotion, as they could not be induced to hop or walk by prodding with
a fine wire. When placed upside down on a flat surface, they could turn
over, but did so slowly, sometimes only after a minute or more had
elapsed. Respiratory throat movements numbered 46 and 60 per minute.
BREEDING
Many observers have noted that breeding activity is initiated by heavy
rains in summer. In my experience precipitation of at least two inches
within a few days is necessary to bring forth large breeding choruses.
With smaller amounts of precipitation only stragglers or small
aggregations are present at the breeding ponds. Tanner (1950: 48) stated
that in three years of observation, near Lawrence, Kansas, the first
storms to bring large numbers of males to the breeding ponds occurred on
June 20, 1947, June 18, 1948, and May 1, 1949.
In 1954 the frogs were recorded first on April 25, but these were under
massive boulders, and were still semi-torpid. Frogs were found fully
active, in numbers, under small flat rocks on May 7. They were found
frequently thereafter. On the afternoon of May 13, the third consecutive
day with temperature slightly above 21° C., low croaking of a frog was
heard among rocks at an old abandoned quarry. Throughout the remainder
of May, calling was heard frequently at the quarry on warm, sunny
afternoons. Often several were calling within an area of a few square
yards, answering each other and maintaining a regular sequence. In the
last week of May rains were frequent, and the precipitation totalled
2.09 inches. On June 1 and 2 also, there were heavy rains totalling 2.26
inches. On the evening of June 2 many frogs were calling at a pond ½
mile south of the Reservation, and one was heard at the pond on the
Reservation. By the evening of June 4, dozens were calling in shallow
water along the edge of this pond in dense _Polygonum_ and other weeds.
There was sporadic calling even in daylight and there was a great
chorus each evening for the next few days, but its volume rapidly
diminished.
In mid-June a system of drift fences and funnel traps was installed 200
yards west of the pond in the dry bottom of an old diversion ditch
leading from the pond. The ditch constituted the boundary between
bottomland pasture and a wooded slope, and therefore was a natural
travelway. The object of the installation was to intercept and catch
small animals travelling along the ditch bottom. The drift fence was
W-shaped, with a funnel trap at the apex of each cone so that the
animals travelling in either direction would be caught. The numbers of
frogs caught from time to time during the summer provided information as
to their responses to weather in migrating to the pond.
TABLE 1. NUMBERS OF FROGS CAUGHT WITHIN TWO DAYS AFTER RAIN IN FUNNEL
TRAPS IN 1954, FROM MID-JUNE, TO THE TIME OF FIRST FROST.
Date Precipitation No. of
in inches caught frogs
July 1 2.02 8
July 10 .11 none
July 16 1.26 none
July 20-21 .94 3
July 24 .38 2
July 28 .29 none
August 1-2 3.22 31
August 6-7-8 2.43 none
August 12 .28 none
August 16 .29 none
August 19-22 .70 none
August 27-28 1.05 none
September 9 .50 none
September 29-30 .38 none
October 4 .74 none
October 12-14 3.51 none
From the positions of the traps and drift fences, it was obvious that
all of the frogs that were caught were travelling toward the pond.
Capture of an equal number moving away from the pond a few days
afterward might have been expected but none at all was caught while
making a return trip. Therefore it seems that the frogs returned by a
different route to their home ranges after breeding. Of necessity they
make the return trip under conditions drier than those that prevail on
the pondward trip, which is usually made in a downpour. Probably the
return travel is slower, more leisurely, and with more tendency to keep
to sheltered situations.
The call is a bleat, resembling that of a sheep, but higher, of lesser
volume, and is not unlike the loud rattling buzz of an angry bee. The
call is usually of three to four seconds duration, with an interval
several times as long. Calling males were floating, almost upright, in
the water within a few yards of shore, where there was dense vegetation.
The throat pouch when fully expanded is several times as large as the
entire head. When a person approached to within a few yards of frogs
they usually stopped calling, submerged, and swam to a place of
concealment.
Having heard the call of typical _G. carolinensis_ in Louisiana, I have
the impression that it is a little shorter, more sheeplike, and less
insectlike than that of _G. olivacea_. The call of _Gastrophryne_ is of
such peculiar quality that it is difficult to describe. Different
observers have described it in different terms. Stebbins (1951: 391) has
described the call in greatest detail, and also has quoted from the
descriptions of it previously published. These descriptions include the
following: "high, shrill buzz"; "buzz, harsh and metallic"; "like an
electric buzzer"; "like bees at close range but more like sheep at a
distance"; "bleating baa"; "shrill, long-drawn quaw quaw"; "whistled
wh[=e][=e] followed by a bleat."
Stebbins observed breeding choruses (_mazatlanensis_) at Peña Blanca
Springs, Arizona, and stated that sometimes three or four called more or
less together, but that they seldom started simultaneously. Occasionally
many voices would be heard in unison followed by an interval of silence,
but this performance was erratic. At the pond on the Reservation I noted
this same tendency many times. After a lull the chorus would begin with
a few sporadic croaks, then four or five or even more frogs would be
calling simultaneously from an area of a few square yards. Anderson
(_op. cit._: 34) found that in small groups of calling _G. carolinensis_
there was a distinct tendency to maintain a definite pattern in the
sequence of the calls. One "dominant" individual would initiate a series
of calls, and others each in turn would take up the chorus.
Pairing takes place soon after the breeding aggregations are formed. On
the night of June 4, 1954, a clasping pair was captured and kept in the
laboratory in a large jar of water. This pair did not separate, and
spawning occurred between noon and 1:30 P. M. on June 5. When the newly
laid eggs were discovered at 1:30 P. M. most of them were in a surface
film. Some were attached to submerged leaves and a few rested on the
bottom. The pair was still joined, but the male was actually clasping
only part of the time, and as the frogs moved about in the water, it
became evident that they were adhering to each other by the areas of
skin contact, which were glued together by their dermal secretion. They
were unable to separate immediately, even when they struggled to do so.
They were observed for approximately 15 minutes before separation
occurred, and during this time they were moving about actively. As they
separated, the area of adhesion was discernible on the back of the
female. It was U-shaped, following the ridges of the ilia and the
sacrum.
On August 2, 1954, after a rain of 3.22 inches, the previously mentioned
funnel trap in the ditch had caught 31 ant-eating frogs. Water had
collected to a depth of several inches in the depression where the trap
was situated. A dozen of the trapped frogs were clasping pairs. These
frogs struggled vigorously as they were removed from the traps, handled
and marked. As a result most of the clasping males were separated from
the females. In handling those of each pair I noticed that they were
glued together by dermal secretions, as were those of the pair observed
on June 5. The areas of adhesion were of similar shape and location in
the different pairs, and included the U-shaped ridge of the female's
back and the male's belly, and the inner surfaces of the male's forelegs
with the corresponding surfaces of the female's sides where the male
clasped.
This adhesion of the members of a pair during mating may be a normal
occurrence. The copious secretion of the dermal glands is of especially
glutinous quality in _Gastrophryne_. The adhesion of members of a pair
may have survival value. These small frogs are especially shy, and in
the breeding ponds they respond to any disturbance with vigorous
attempts to escape and hide. Under such circumstances the adhesion may
prevent separation. Also, it may serve to prevent displacement of a
clasping male by a rival. Anderson (_op. cit._) who observed many
details of the mating behavior of _G. carolinensis_, both in the
laboratory and under natural conditions, mentioned no such adhesion
between members of a pair.
Anderson (_op. cit._: 31) discussed the possibility that reproductive
isolation might arise in sympatric populations, such as those of _G.
carolinensis_ in southern Louisiana, through inherent differences in
time of spawning. However, in _G. olivacea_ at least, such isolation
would be prevented by individual males returning to breed at different
times in the same season. Furthermore, individual differences in choice
of breeding time probably result from environmental factors rather than
genetic factors in most instances. In _G. olivacea_ in Kansas, time of
breeding is controlled by the distribution of heavy rainfall creating
favorable conditions. Onset of the breeding season may be hastened or
delayed, or an entire year may be missed because of summer drought. If
favorable heavy rains are well distributed throughout the summer, frogs
of age classes that are not yet sexually mature in the early part of
the breeding season, may comprise the bulk of the breeding population in
late summer.
DEVELOPMENT OF EGGS AND LARVAE
Eggs laid on June 5 by the pair kept in the laboratory were hatching on
June 7, on the average approximately 48 hours from the time of laying.
By June 8 all the eggs had hatched and the tadpoles were active. On
August 28 and 29 thousands of newly metamorphosed young were in evidence
on wet soil at the pond margin; in some the head still was tadpolelike
and they had a vestige of the tail stump. These young were remarkably
uniform in size, 15 to 16 mm. (the smallest one found was 14½ mm.)
and almost all of them had originated from eggs laid after heavy
precipitation, totalling 3.22 inches, in the first 36 hours of August.
Allowing one day for adults to reach the pond and spawn, and two days
more for eggs to hatch, the tadpole stage must have lasted approximately
24 days in this crop of young.
Wright and Wright (1949: 582) stated that the tadpoles metamorphosed
after 30 to 50 days, and that the newly metamorphosed frogs are 10 to 12
mm. in length. Length of time required for larval development probably
varies a great deal depending on the interaction of several factors such
as temperature and food supply.
GROWTH
Little has been recorded concerning the growth rate of _Gastrophryne_ or
the time required for it to attain sexual maturity. Wright (1932) found
that _G. carolinensis_ in the Okefinokee Swamp region has a mean
metamorphosing-size of 10.8 mm. Young thought to be those recently
emerged from their first hibernation were those in the size group 15.0
to 20.0 mm., while the frogs in the 20 to 27 mm. size class and those in
the 27 to 36 mm. class were interpreted as representing two successively
older annual age classes. Anderson (1954: 41) thought he could recognize
four successive annual age classes in the same species in southern
Louisiana. He found that sexual maturity is attained at a length of 21
to 24 mm. in frogs which he believed to be late in the second year of
life.
Allowing for size differences between the two species, Wright's and
Anderson's conclusions regarding growth in _G. carolinensis_, on the
basis of size groups, are largely substantiated by my own data on the
growth of marked individuals of _G. olivacea_ living under natural
conditions in Kansas.
In 1954, an opportunity to investigate the early growth was afforded by
unusually favorable circumstances. The population of frogs that emerged
from hibernation in the late spring of 1954 included few, if any, that
were below adult size; drought had prevented successful breeding in 1952
and 1953. Heavy rains in the first week of June, 1954, and again in the
first week of August, resulted in the production of two successive crops
of young so widely spaced that they were easily distinguishable. Some
young may have been hatched after other minor rains, but certainly these
were relatively few. Young from the eggs laid in the first week of
August were metamorphosing during the last week of August. Growth in the
frogs of this group can be shown by the average size and the size range
of the successive samples collected.
TABLE 2. GROWTH IN FROGS METAMORPHOSED IN THE LAST WEEK OF AUGUST, 1954.
=========================================================
|Number in| Mean size |Size range
Time of sample | sample | in mm. | in mm.
--------------------+---------+--------------+-----------
August 27 to 31 | 27 | 15.55 ± .079 | 15 to 17
--------------------+---------+--------------+-----------
September 11 | 114 | 17.2 ± .033 | 14 to 20
--------------------+---------+--------------+-----------
September 15 to 22 | 12 | 18.7 ± .090 | 16 to 20
--------------------+---------+--------------+-----------
September 27 to 30 | 37 | 19.3 ± .055 | 17 to 21.5
--------------------+---------+--------------+-----------
October 1 to 7 | 62 | 20.8 ± .072 | 17 to 24
--------------------+---------+--------------+-----------
October 12 to 17 | 49 | 22.3 ± .092 | 18 to 24
=========================================================
By mid-October, six weeks after metamorphosis, these frogs had increased
in over-all length by approximately 50 percent. Having grown a little
more than 1 mm. per week on the average, they were approximately
intermediate in size between small adults and newly metamorphosed young.
The frogs hatched in June were present in relatively small numbers
compared with those hatched in August, and were not observed
metamorphosing. In late August a sample of 33 judged to belong to the
June brood averaged 26.2 (22-28) mm. long. A sample of 39 from the first
week of October averaged 28.1 (24.5-32) mm. Frogs of this group thus
were approaching small adult size late in their first growing season.
Such individuals possibly breed in the summer following their first
hibernation, when they are a year old or a little more. Because
recaptured frogs were not sacrificed to determine the state of their
gonads, the minimum time required to attain sexual maturity was not
definitely determined. The available evidence indicates that sexual
maturity is most often attained late in the second year of life, at an
age of approximately two years. The darkened and distensible throat
pouch of the adult male probably is the best available indicator of
sexual maturity.
[Illustration: FIG. 3. Growth shown by successive samples of young
ant-eating frogs of two size groups in late summer and early fall of
1954. For each sample the mean, standard deviation, and range are shown.
Lower series are those metamorphosed in late August, and upper series
are those metamorphosed in late June.]
[Illustration: FIG. 4. Rapid growth of a young female caught in June,
July, and August, 1949. Presumably this individual metamorphosed late in
the summer of 1948, and at the age of approximately one year it was near
small adult size.]
Frogs that metamorphose in late summer have little time to grow before
hibernating, and still are small when they emerge in spring. The
smallest one found was 19 mm. long (May 19, 1951), and in each year
except 1954 many such young were found that were less than 25 mm. in
length in May or early June. None of the frogs marked at or near
metamorphosing size has been recaptured, but the trend of early growth
is well shown by Table 2 and Fig. 3. However, many juveniles that were
captured and marked within a few weeks of metamorphosis were recaptured
as adults. The selected individuals in Table 3 are considered typical of
growth from "half-grown" to small adult size. Growth in many other
individuals is shown in Figs. 6 and 7.
TABLE 3. GROWTH IN FROGS MARKED AS YOUNG AND RECAPTURED AS SMALL ADULTS.
==============================================================
Individual | Dates | Length | Probable time
and sex | of capture | in mm. |of metamorphosis
-----------------+-----------------+---------+----------------
No. 1 [Female] | August 28, 1951 | 21.5 |Mid-July, 1951
| May 5, 1952 | 23 |
| July 3, 1952 | 32 |
| August 31, 1952 | 33 |
-----------------+-----------------+---------+----------------
No. 2 [Female] | June 8, 1950 | 25 |Late July, 1949
| May 24, 1951 | 31 |
| July 30, 1951 | 34 |
| June 24, 1952 | 35 |
-----------------+-----------------+---------+----------------
No. 3 [Male] | August 31, 1951 | 24 |Late June, 1951
| May 23, 1953 | 32 |
==============================================================
[Illustration: FIG. 5. Ant-eating frogs, a little less than twice
natural size, adult and newly metamorphosed young, showing differences
in size and coloration. The young is darker and has a leaflike middorsal
mark which fades as growth proceeds.]
The trend of growth after attainment of minimum adult size is also well
shown by the records of marked individuals recaptured. Many of these
were marked while they were still small so that their approximate ages
are known. For those recaptured in their second year, after one
hibernation, length averaged 30.92 mm. Some of this group were young
metamorphosed late the preceding summer and still far short of adult
size (as small as 23 mm.) when recaptured. Others were relatively large,
up to 33 mm. A group of 22 recaptured frogs known to be in their third
year averaged 33.3 mm. (males 31.9, females 35.3, excluding four
individuals of undetermined sex). Fifteen other recaptured frogs were
known to be in their fourth year at least, and some probably were older,
as they were already large adults when first examined. These 15 averaged
36.6 mm. (males 34.7, females 37.9 mm.). Size was similar in a sample of
58 individuals intercepted en route to the breeding pond in heavy rains
of June and August, 1954. The 38 males in this sample ranged in size
from 30 mm. to 38 mm., averaging 34.5. The 20 females ranged from 34 mm.
to 40 mm., averaging 37.65. The large average and maximum size in this
sample of a breeding population may be typical after periods of drought
years have prevented successful reproduction. Summer drought in 1952 and
1953 prevented breeding in those years, or, at least, it drastically
reduced the numbers of young produced. One-year-old and two-year-old
frogs may not have been represented at all in the sample of 58.
Three-year-old frogs presumably made up a substantial part of the
sample, since 1951 was a year of successful breeding.
[Illustration: FIG. 6. Growth in a group of frogs, each marked while
still short of adult size and mostly recaptured after lapse of one or
more hibernation periods. Each line connects records of an individual
frog.]
Differences in size between species and geographic variation in size in
_Gastrophryne_ have been given little attention by herpetologists, but
if understood, would help to clarify relationships. Hecht and Matalas
stated in their revision (1946: 5) that size is of no importance as a
taxonomic character, as typical _carolinensis_, _olivacea_, and
_mazatlanensis_ all averaged approximately the same--26 to 28
mm.--females slightly larger than males. However, they arbitrarily
classed as adults all individuals 22.5 mm. in length or larger, having
found individuals this small that showed the darkened and distensible
throat pouches characteristic of adult males. From the trend of my own
measurements of _G. olivacea_ in northeastern Kansas, I conclude that
either many immature individuals were included in their samples, or that
the populations sampled included some with individuals that were
remarkably small as adults.
[Illustration: FIG. 7. Growth in another group of frogs that were marked
as young or small adults and recaptured after intervals of more than a
year. Frogs of this group were, on the average, larger than the
individuals shown in Fig. 6, and they made less rapid growth.]
The population which I studied may be considered typical of _G.
olivacea_. They averaged large, including individuals up to 42 mm. in
length, well above the maximum sizes for any reported in the literature.
At metamorphosis these _olivacea_ are of approximately 50 percent
greater length than _G. carolinensis_ as reported by Wright and Wright
(1949: 573) and Anderson (1954: 41). Yet Blair (1950: 152) observed that
in eastern Oklahoma, where the ranges of _olivacea_ and _carolinensis_
overlap, the latter is larger. On the basis of field and laboratory
observations he tentatively concluded that one of the main barriers to
interbreeding was the reluctance of the males of _carolinensis_ to clasp
the smaller females of _olivacea_.
That size differs in different populations, and is still poorly
understood, is illustrated by the following discrepant figures from
various authors.
TABLE 4. SIZE RANGE OF ADULTS IN VARIOUS POPULATIONS OF GASTROPHRYNE.
===============+=======================+=================+=============
Species or | Geographic population | Authority |Size range of
subspecies | sampled | |adults in mm.
---------------+-----------------------+-----------------+-------------
| | |
_olivacea_ |Douglas Co., Kansas |present study | 31 to 42
| | |
_olivacea_ |entire range |Wright and Wright| 19 to 38
| | (1949) |
| | |
_carolinensis_ |entire range |Wright and Wright| 20 to 36
| | (1949) |
| | |
_carolinensis_ |southern Louisiana |Anderson | 22 to 35
| | (1954) |
| | |
_areolata_ |southeastern Texas |Wright and Wright| 23 to 29
| | (1949) |
| | |
_mazatlanensis_|Arizona and New Mexico |Wright and Wright| 22 to 30
| | (1949) |
| | |
_mazatlanensis_|Santa Cruz Co., Arizona|Stebbins | 25.2 to 31.5
| | (1951) |
---------------+-----------------------+-----------------+-------------
COLOR AND PATTERN
The color pattern changes in the course of development, and the shade of
color changes in response to environmental conditions. At the time of
metamorphosis, young are dark brown with specks of black and with a
dark, cuneate, leaflike middorsal mark. The narrow end of this mark
arises just behind the head, and the mark extends posteriorly as far as
the hind leg insertions. At its widest, the mark covers about half the
width of the dorsal surface. The lateral edges of the mark are sharply
defined, but at its anterior and posterior ends it blends into the
ground color. In most individuals smaller than 20 mm., this dorsal mark
is well defined and conspicuous. As growth proceeds, however, it becomes
faint. In frogs 19 to 25 mm. long the marks have disappeared. In
individuals of this size the brown ground color is markedly paler than
in those newly metamorphosed, but is darker than in adults.
In large adults the dorsal coloration is a uniform pale tan, paler on
the average in females than in males. Temperature and moisture both
affect the shade of coloration. In frogs that were partly desiccated,
the color was unusually pale, with a distinctly greenish tint, and at
high temperatures coloration tended to be relatively pale.
Hecht and Matalas (1946) have described and figured color patterns in
various populations of _Gastrophryne_, demonstrating geographic trends
and helping to clarify relationships. Their account indicates that the
dark dorsal mark present in young of _olivacea_ but not present in
adults, is better developed and longer persisting in other forms.
Specimens of _carolinensis_, presumably adult, are figured which have
the dark middorsal area contrasting with paler color of the sides. The
dark area is seen to consist of dots or blotches of black pigment which
may be in contact producing more or less continuous black areas, or may
be separate and distinct producing a spotted pattern. Pigmentation is
usually most intense along the lateral edges of the dorsal leaflike
mark; the central portion may be so much paler that the effect is that
of a pair of dorsolateral stripes. This latter type of pattern is best
developed in the population of Key West, Florida. Hecht and Matalas did
not consider these insular frogs to be taxonomically distinct, because
only 48 percent of specimens from the Florida keys had the "Key West"
pattern, while 29 per cent resembled _olivacea_ and 23 per cent
resembled _carolinensis_. In the southwestern subspecies (or species)
_mazatlanensis_, recorded from several localities in Sonora and from
extreme southern Arizona, the dorsal pigmentation similarly tends to be
concentrated in dorsolateral bands, but is much reduced or almost
absent, and there is corresponding pigmentation dorsally across the
middle of the thigh, across the middle of the shank, and on the foot.
When the leg is folded, these three dark areas are brought in contact
with each other and with the dorsolateral body mark, if it is present,
to form a continuous dark area, in a characteristic "ruptive" pattern.
Hecht and Matalas found similar leg bars, less well developed, in
certain specimens of _olivacea_ including one from Gage County,
Nebraska, at the northern end of the known geographic range.
MOVEMENTS
Freiburg (_op. cit._: 384) concluded that ant-eating frogs seem to have
no individual home ranges, but wander in any direction where suitable
habitat is present. However, from records covering a much longer span of
time, it became increasingly evident that a frog ordinarily tends to
stay within a small area, familiar to it and providing its habitat
requirements.
Nevertheless, in all but a few instances the marked frogs recaptured
were in new locations a greater or lesser distance from the site of
original capture. The movements made by these frogs were of several
distinct types:
1. Routine day to day movements from shelter to shelter within
the area familiar to the animal, the "home range."
2. Shifts from one home range to another; such shifts may have
been either long or short, and may have occurred abruptly or
by gradual stages.
3. Travel by adults to or from a breeding pond. In most or all
instances these adults were regularly established in permanent
home ranges, and they often moved through areas unsuitable
as habitat to reach the ponds.
4. Movements of dispersal in the young, recently metamorphosed
and not yet settled in a regular home range.
Usually there was uncertainty as to which types of movements had been
made by the recaptured individuals. Some may have made two or three
different types of movements in the interval between captures.
On many occasions individuals were found beneath the same rock on two
consecutive days, or occasionally on several successive days. Rarely,
such continued occupancy of a niche lasted several weeks. In 1949, a
frog was found under the same rock on June 4, 6, 26, 27, and July 1, 3
and 11. This was an immature female, presumably metamorphosed late in
the summer of 1948. During the five weeks period covered by the records,
it grew from 27 mm. to 34 mm. In 1952, another individual was found
under its home rock on June 23 and 30, July 2 and 3, and August 14 and
20. In 1952 a juvenile was found under a rock on May 30, June 4, and
June 17. These three individuals were exceptional in their continued
occupancy of the same niches. Among the hundreds of others recorded,
none was found more than twice in any one place.
Despite the fact that field work was concentrated on small areas which
were worked intensively, only eight per cent of the frogs recorded were
ever recaptured, and most of those were recaptured only once. Only 13
individuals yielded series of records, well spaced, in two or more
different years. These few individuals recaptured frequently may not be
typical of the entire population. The low incidence of recaptures
indicates that relatively few of the frogs present on an area at any one
time have been taken. Because of their secretive and subterranean habits
most of the frogs are missed by a collector who searches by turning
rocks, or trapping with pitfalls. Therefore, even though a marked frog
may survive and remain within a radius of a few hundred feet of one
point for months or even years, the chances of recapture are poor.
One female was caught first as a juvenile on June 8, 1950. On April 24,
1951, when first recaptured, she had grown to small adult size, and was
only 18 feet from the original location. On July 30, 1951, however, she
was recaptured 750 feet away. At a fourth capture on May 21, 1952, she
had shifted 70 feet farther in the same direction. At the final capture
on June 24, 1952, she was approximately 140 feet from both the third and
fourth locations. The sequence of these records suggests that the frog
had already settled in a home range at the time of her first capture in
1950, and that approximately a year later she shifted to a second home
range, which was occupied for the following year, at least.
[Illustration: FIG. 8. Distances between captures in frogs marked, and
recaptured after substantial intervals including one or more
hibernations. Distances are grouped in 25-foot intervals. For longer
distances the trend is toward progressively fewer records, indicating
that typical home ranges are small.]
In several instances, after recaptures as far as 400 feet from the
original location, frogs were again captured near an original location,
suggesting that for some individuals, at least, home ranges may be as
much as 400 feet in diameter.
Figure 8 shows that for movements of up to 400 feet, numbers of
individuals gradually decrease with greater distance. For distances of
more than 400 feet there are comparatively few records. Of the 59
individuals recaptured after one or more hibernations, only nine had
moved more than 400 feet from the original location. Twenty-five were
recaptured at distances of 75 feet or less. The mean distance for
movement for all individuals recaptured was 72 feet. A typical home
range, therefore, seems to average no more than 75 feet in radius. Of
the 59 individuals recaptured after one or more hibernations, 47 were
adults and probably many of these had made round-trip migrations to the
breeding pond. This was not actually demonstrated for any one
individual, but several were captured in each of three or four different
years near the same location.
[Illustration: FIG. 9. Distances between captures and elapsed time in
months in marked frogs recaptured. Few records are for distances more
than 400 feet. There is but little tendency to longer movements in those
caught after relatively long intervals.]
The trend of movements differed in the sexes. Males are more vagile. Of
21 adult males recaptured, none was less than 40 feet from its original
location, whereas six of the 26 adult females were less than 40 feet
away from the original point of capture. Of seven frogs that had
wandered 700 feet or more, five were males.
FOOD HABITS
According to Smith (1934: 503) stomachs of many specimens, from widely
scattered localities in Kansas, contained only large numbers of small
ants. Tanner (1950: 47) described the situation of a frog found on the
Reservation buried in loose soil beneath a flat rock, beside an ant
burrow, where, presumably, the frog could snap up the passing ants
without shifting its position. Anderson (_op. cit._: 21) examined
alimentary tracts of 203 specimens of _carolinensis_ from Louisiana,
representing a year round sample for several different habitats. He
found a variety of small animals including ants, termites, beetles,
springtails, bugs, ear-wigs, lepidopterans, spiders, mites, centipedes,
and snails. Most of these prey animals were represented by few
individuals, and ants were much more numerous than any of the other
groups. Anderson concluded that ants, termites, and small beetles were
the principal foods. He noted that some of the beetles were of groups
commonly found in ant colonies. Tanner reported that in a large number
of the frogs which he collected in Douglas, Riley, Pottawatomie, and
Geary counties, Kansas, the digestive tracts and feces contained only
ants. Wood (1948: 226) reported an individual of _G. carolinensis_ in
Tennessee found under a flat rock in the center of an ant nest.
Freiburg (_op. cit._: 383) reported on the stomach contents of 52
ant-eating frogs collected near the Reservation. Ants constituted nearly
all these stomach contents, though remains of a few small beetles were
found. The ants eaten were of two kinds, _Lasius interjectus_ and
_Crematogaster_ sp. The latter was by far the more numerous.
Although I made no further study of stomach contents, the myrmecophagous
habits of _Gastrophryne_ have come to my attention frequently in the
course of routine field work. Individuals kept in confinement for a day
or more almost invariably voided feces which consisted mainly or
entirely of ant remains, chiefly the heads, as these are most resistant
to digestion.
Often upon examining frogs I have found ants (_Crematogaster_ sp.) or
their severed heads, attached with mandibles embedded in the skin. To
have been attacked by ants, the frogs must have been in or beside the
ants' burrow systems. Frequently the frogs that were uncovered beneath
rocks were adjacent to clusters of ants or to their nests or travelways,
in a position strategically located to feed upon them, as described by
Tanner. Often the feces of the frogs were found in pitfalls or under
flat rocks. Although these feces were not analyzed, they seemed to
consist mainly or entirely of ant remains.
The species of _Crematogaster_, which is the chief food of
_Gastrophryne_ in this region, is largely subterranean in habits, and is
extremely abundant. Any flat rock in damp soil is likely to harbor a
colony beneath it. Colonies are situated also in damp soil away from
rocks, beneath almost any kind of debris, and in hollow weed stalks and
decaying wood. Live-traps for small mammals, having nest boxes attached,
almost always were occupied by colonies of _Crematogaster_, if they were
left in the field in warm, humid weather. Occasionally the ants attacked
and killed small mammals caught in such traps. Among the thousands of
kinds of insects occurring on the Reservation, this ant is one of the
most numerous in individuals, one of the most important on the basis of
biomass and provides an abundant food source for those predators that
are ant eaters. Food supply probably is not a limiting factor to
populations of _Gastrophryne_ on the area.
PREDATION
Young copperheads are known to feed upon ant-eating frogs occasionally
(Anderson, 1942: 216; Freiburg, 1951: 378). Other kinds of snakes
supposedly eat them also. The common water snake (_Natrix sipedon_) and
garter snake (_Thamnophis sirtalis_) probably take heavy toll of the
adults at the time they are concentrated at the breeding pools. Larger
salientians may be among the more important enemies of the breeding
adults, the tadpoles, and the newly metamorphosed young. Bullfrogs
(_Rana catesbeiana_) and leopard frogs (_Rana pipiens_) are normally
abundant at the pond on the Reservation. These large voracious frogs
lining the banks are quick to lunge at any moving object, and must take
heavy toll of the much smaller ant-eating frogs that have to pass
through their ranks to reach the water. The newly metamorphosed young
often are forced to remain at a pond's edge for many days, or even for
weeks, by drought and they must be subject to especially heavy predation
by ranid frogs. Even the smallest newly metamorphosed bullfrogs and
leopard frogs would be large enough to catch and eat them.
As a result of persistent drought conditions in 1952 and 1953, bullfrogs
were completely eliminated from the pond by early 1954. Re-invasion by a
few individuals occurred in the course of the summer; these probably
made long overland trips from ponds or streams that had persisted
through the drought. Leopard frogs reached the pond in somewhat larger
numbers, but their population in 1954 was only a small percentage of
that present in most other years. Notable success in the ant-eating
frog's reproduction in 1954 may have been due largely to the scarcity of
these large ranids at the breeding ponds.
Freiburg (_loc. cit._) noted that many of the ant-eating frogs he
examined were scarred, and some had digits or limbs amputated. He did
not speculate concerning the origin of these injuries. However, it seems
likely that many or all of them were inflicted by the short-tailed shrew
(_Blarina brevicauda_). Five-lined skinks living on the same area were
likewise found to be scarred by bites which I identified (Fitch, 1954:
133) as bites of the short-tailed shrew. This shrew is common on the
Reservation, especially in woodland. Many have been trapped in the
pitfalls. On several occasions when a short-tailed shrew was caught in
the same pitfall with ant-eating frogs, it was found to have killed and
eaten them. Like the frogs, the shrews were most often caught in
pitfalls just after heavy rains. Once in 1954 a shrew was found at the
quarry in a pitfall that had been one of those most productive of frogs.
The bottom of the pitfall was strewn with the discarded remains (mostly
feet and skins) of perhaps a dozen ant-eating frogs. All had been eaten
during one night and the following morning, as the trap had been checked
on the preceding day. On other occasions shrews caught in pitfalls with
several frogs had killed and eaten some and left others unharmed.
SUMMARY
In northeastern Kansas the ant-eating frog, _Gastrophryne olivacea_, is
one of the more common species of amphibians. This area is near the
northern limits of the species, genus, and family. The species prefers a
dry, rocky upland habitat often in open woods or at woodland edge where
other kinds of salientians do not ordinarily occur. It is, however,
tolerant of a wide variety of habitat conditions, and may occur in river
flood plains or cultivated land. In these situations where surface rocks
are absent, cracks and rodent burrows presumably furnish the
subterranean shelter that it requires.
This frog is secretive and spends most of the time in subterranean
shelter, obtaining its food there rather than in the open. Only on warm
rainy nights is it inclined to venture into the open. Then, it moves
about rapidly and with a scuttling gait, a combination of running and
short hops. However, it may be flushed in daylight from a hiding place
by the vibrations from footsteps of a person or an animal, or it may
move about in the daytime when temperatures at night are too low for
activity. Though not swift of foot, the frogs are elusive because of
their tendency to keep under cover, their slippery dermal secretion, and
the ease with which they find and enter holes, or crevices to escape.
Breeding occurs at any time from late May through August and is
controlled by the distribution of rainfall. Heavy precipitation,
especially rains of two inches or more, stimulates the frogs to migrate
in large numbers to breeding ponds. Even though there are several well
spaced periods of unusually heavy rainfall in the course of a summer,
each one initiates a new cycle of migration, mating and spawning. Heavy
rainfall is a necessity, not only to ensure a water supply in temporary
pools where the frogs breed, but to create the moist conditions they
require for an overland migration. An individual male may migrate to a
pond and breed at least twice in the same season. Whether or not the
females do likewise is unknown. Amplexus and spawning occur mainly
within a day or two after the frogs reach the ponds. The males call
chiefly at night, but there may be daytime choruses when breeding
activity is at its peak. Many males concentrate within a few square
yards in the choruses and float upright usually beside or beneath a stem
or leaf, or other shelter, rendering them extremely inconspicuous. The
call is a bleat of three seconds duration, or a little more. In amplexus
the members of a pair sometimes become glued together by their viscous
dermal secretions. The eggs hatch in approximately 48 hours. The
tadpoles metamorphose in as few as 24 days. Newly metamorphosed frogs
are 15 to 16 mm. in length, or, rarely as small as 14.5 mm. They are
thus much larger than newly metamorphosed _G. carolinensis_, which have
been described as 10-12 mm. or even as small as 8.5 mm. The newly
metamorphosed frogs disperse from the breeding ponds as soon as there is
a heavy rain. The young grow a little more than one mm. in length per
week. Those metamorphosed in early summer may attain minimum adult size
before hibernation which begins in October. It seems that sexual
maturity is most often attained in the second season, at an age of one
to two years.
_Gastrophryne_ belongs to a family that is primarily tropical in
distribution, and frogs of this genus have much higher temperature
thresholds than most other amphibians of northeastern Kansas, with a
correspondingly short season of activity. For more than half the year,
mid-October to early May the frogs are normally in hibernation. Body
temperatures of active frogs ranged from 17.0° C. to 37.6° C., but more
than two-thirds were within the relatively narrow range, 24.0° to 31°.
Near the date of the first autumn frost the frogs disappear from the
soil surface and from their usual shelters near the surface, presumably
having retired into hibernation in deep holes and crevices.
The natural enemies include young of the copperhead. The bullfrog and
leopard frog probably take heavy toll of both the adults and the newly
metamorphosed young at the breeding ponds. Reproductive success of the
ant-eating frogs was much greater in 1954 when these ranids were
unusually scarce. The short-tailed shrew is an important enemy. On
occasion it took heavy toll of frogs trapped in pitfalls, and many of
the larger adults were scarred or mutilated from bites, probably of the
shrew.
Each of several frogs was found consistently under the same rock for
periods of weeks. The hundreds of other frogs that were marked were
rarely found twice in any one spot. Usually an individual recaptured
after weeks or months was still near the original site. In many
instances the distance involved was only a few yards, but there is some
evidence that home ranges may be as long as 400 feet in greatest
diameter. Of those caught in two or more different years only 15 per
cent were shown to have moved more than 400 feet. These few
exceptionally long movements, up to 2000 feet, involve shifts in home
range or migrations motivated by reproductive urge.
LITERATURE CITED
ANDERSON, P.
1942. Amphibians and reptiles of Jackson County, Missouri. Bull.
Chicago Acad. Sci., 6: 203-220.
ANDERSON, P. K.
1954. Studies in the ecology of the narrow-mouthed toad, Microhyla
carolinensis carolinensis. Tulane Studies in Zool., 2: 15-46.
BLAIR, A. P.
1950. Note on Oklahoma microhylid frogs. Copeia, 1950: 152.
BOGERT, C. M.
1949. Thermoregulation in reptiles, a factor in evolution.
Evolution, 3: 195-211.
BRAGG, A. N.
1943. Observations on the ecology and natural history of Anura, XV.
The hylids and microhylids in Oklahoma. Great Basin Nat.,
4: 62-80.
de CARVALHO, A. L.
1954. A preliminary synopsis of the genera of American microhylid
frogs. Occas. Papers Mus. Zool. Univ. Michigan, no. 555: 19
pp., 1 pl.
DICE, L. R.
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_Transmitted February 28, 1955._
* * * * *
Transcriber's Notes
A small number of inconsistencies and typographical errors have been
changed in the text as follows:
p. 279 "near-by" changed to "nearby" (in nearby counties of Kansas)
p. 289 "successivly" changed to "successively" (two successively older
annual age classes)
p. 297 "per cent" changed to "percent" (only 48 percent of specimens from
the Florida keys)
p. 303 "famliy" changed to "family" (the northern limits of the species,
genus, and family.)
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