Comparative Prey-Attack Studies in Newborn Snakes of the Genus Thamnophis

Abstract

Garter snakes (Thamnophis) from five species (including three subspecies of one form) were tested several days after birth with water extracts of at least 12 small animals (1.5 g animal to 10 ccm warm distilled water). The 12 prey animals included three species of earthworms and three of fish, a salamander and its larva, a frog, a leech, a slug and a baby mouse. A distilled water swab elicited tongue flicking only, while certain extract swabs resulted in actual prey-attack behavior after at least one tongue flick. A score was given to each extract test using a simple formula based upon tongue flick frequency and attack latency. Differences and similarities between the species were found and are discussed in relation to the actual feeding preferences in nature and captivity. For example, the aquatic Thamnophis elegans aquaticus attacked only the extracts made from the salamander larva, the frog, and the three fish; Thamnophis sirtalis also attacked the leech and the three earthworm extracts. It is suggested that the perceptual selectivity shown by naive snakes is an evolutionary response to present and past ecological conditions. The ability of newborn snakes to rapidly acquire a food avoidance response was also demonstrated.