Antipredator behaviour of hatchling snakes: effects of incubation temperature and simulated predators

All animals that are exposed to predators must distinguish dangerous from nondangerous threats and respond correctly. In reptiles, emerging hatchlings are vulnerable to a wide range of predators, particularly if they emerge during daylight. In these experiments I tested the response of pine snake, Pituophis melanoleucus, hatchlings incubated at 22-23, 27-28, or 32-33 degrees C to visual and vibratory stimuli to examine antipredator behaviour. Emerging hatchlings were exposed to one of five conditions: (1) hawk model, (2) white head model. with no facial features, (3)white head model with black eyes, (4) a person, or (5) a vibration without a visual stimulus. I tested the null hypotheses of no differences in response as a function of predator type or incubation temperature. Emergence behaviour when undisturbed was affected by incubating temperature, and antipredatory behaviour was affected by both predator type and incubation temperature. Pine snake hatchlings responded more protectively (withdrawal into tunnels) than defensively (striking), responded with less intensity to a vibration compared with visual predator stimuli, and required longer to respond to a head model without eyes than to all other predator types. Given the relatively small size of hatchlings, it is adaptive for them to withdraw into the nest rather than attack a predator. Hatchlings from eggs that were incubated at medium temperatures required less time to emerge from their underground nests when undisturbed, and had stronger protective responses than snakes incubated at other temperatures. These results suggest that hatchlings incubated at medium temperatures are generally less vulnerable to predators than hatchlings incubated at higher or lower temperatures. (C) 1998 The Association for the Study of Animal Behaviour.