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.