Description and Preliminary Analysis of Antipredator Behavior of Rhabdophis tigrinus tigrinus, a Colubrid Snake with Nuchal Glands

Abstract

Antipredator responses of adult and hatchling Rhabdophis tigrinus tigrinus were investigated in the laboratory and field. In laboratory experiments 1 and 2, the snakes were repeatedly pinned at neck, body, and tail with a snake hook at ambient temperatures of approximately 15•Ž and 25•Ž. In laboratory experiment 3, hatch-lings were confronted with a nonmoving and moving human hand (non-physical contact stimulus) and tapped by a human hand (physical contact stimulus). Field observations were made when snakes were captured in their natural habitat. A total of 17 types of antipredator responses were recognized. Among them, characteristic responses frequently observed were neck flattening, body flattening, neck arching, jerking, neck butting , and open mouth. "Dorsal facing posture", in which snakes keep the dorsal neck region directed toward the physical contact stimulus, was also a characteristic response of the snakes. Ambient temperature, type of stimulus, body part stimulated, and age of snakes affected the antipredator responses in R. t. tigrinus. Neck arching was more frequently observed at 15•Ž than at 25•Ž and flight response was more freq exhibited at 25•Ž than at 15•Ž in adults. Neck/body flattening, neck arching, st and flight were more frequently elicited by the tapping stimulus than by nonmoving and moving stimuli in hatchlings. Individual differences in antipredator responses were observed in adults. Characteristic antipredator behaviors of R. t. tigrinus such as neck flattening, neck arching, and dorsal facing posture seemed to be associated with the presence of the nuchal glands, suggesting a predator deterrent function of the glands.