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 deg. C. to 37.6 deg. C.,
but more than two-thirds were within the relatively narrow range, 24.0
deg. to 31 deg.. 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.