Development of antipredator responses in snakes: I. Defensive and open-field behaviors in newborns and adults of three species of garter snakes (Thamnophis melanogaster, T. sirtalis, T. butleri).

Abstract

A comparative study of defensive behavior in multiple litters of newborn garter snakes and adult female garter snakes from three species was conducted in the laboratory. In Experiment 1, 241 one-day old snakes, roughly equally divided among the three species, were tested for defensive behaviors directed towards a moving or nonmoving stimulus. Thamnophis melanogaster babies were by far the most reactive in terms of strikes, bites, and defensive tongue-flicks. Thamnophis sirtalis and Thamnophis butleri were far less reactive and not significantly different from each other. In Experiment 2, adult females of each species reacted in ways similar to the neonates with the exception that the T. sirtalis females were more reactive towards the moving stimulus than were the T. butleri females. Experiment 3 showed large and significant differences in openfield behavior among the three species, but few significant correlations between open-field measures and antipredator responses. Although neonates in altricial species typically rely on adults for defense against predators, members of precocial species with no parental care must be ready to cope with potential predators soon after birth, which has consequences for subsequent behavioral development (cf. Burghardt, 1984). Snakes are among the most precocial of terrestrial vertebrates and are capable of engaging in defensive responses from the moment they are born, sometimes even before totally emerged from the egg in oviparous species (Burghardt, 1978). Because snakes exhibit a variety of defensive behaviors, they are excellent subjects for the comparative study of antipredator displays in closely related species prior to any effects of postnatal experience. This approach has been used successfully to examine innate differences in response to chemical cues from prey among closely related species of snakes (e.g., Burghardt, 1969) but has not previously been systematically extended to the study of neonatal antipredator behaviors. Although there are many anecdotal reports of defensive behavior in snakes (Greene, in press), few investigators have attempted to apply quantitative techniques to the study of