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.