Is headfirst ingestion essential in gape-limited predators? Prey-handling behavior of the anurophagous snake Rhabdophis tigrinus (Colubridae)

Abstract

Headfirst ingestion of prey is a common adaptive behavioral trait in gape-limited predators that swallow large prey whole. To ascertain this tendency during anurophagy, prey handling and direction of prey ingestion were investigated in Rhabdophis tigrinus (Boie, 1826), a snake that feeds mainly on anurans. Examinations of stomach contents of wild R. tigrinus revealed that this snake does not show a tendency for headfirst ingestion of large prey, unlike most other snake species. In the laboratory, direction of ingestion depended largely on initial bite position, and when R. tigrinus swallowed a frog rump-first, the snake grasped both hind limbs of the frog and aligned them side by side so that both were swallowed together simultaneously from their tips. A simple model test suggested that physical resistance in the buccal cavity incurred during transportation of frogs may not differ between headfirst and hind-first ingestion if the hind limbs of frogs are aligned and swallowed simultaneously. Laboratory experiments also demonstrated that ingestively naive hatchlings of R. tigrinus are able to perform the unique manipulation required to swallow frogs hind-first. It is suggested that this unique ingestion mode is an adaptation for anurophagy, and several possible functional advantages are discussed.