Development of antipredator responses in snakes: IV. Interspecific and intraspecific differences in habituation of defensive behavior.

Habituation of defensive attacks directed toward a threatening stimulus was investigated in neonatal garter snakes. The focus of the experiments was on differential effects of a simple experimental process in relation to species, litter, sex, and individual. In Experiment 1 newborn Thamnophis melanogaster from four liters and newborn Thamnophis butleri from three liters were given daily tests in which snakes were confronted with a nonmoving and moving human hand. Over five successive test days the T melanogaster neonates showed a decline in number of strikes directed toward the stimuli. When retested 10-13 days later the animals showed significant response recovery. Although some of the T? butleri newborns demonstrated significant habituation, there was no overall habituation of strike scores in this species. The T? melanogaster had high strike scores, more rapid habituation to moving than nonmoving stimuli, and significant liter differences in habituation rates. The T? melanogaster, but not the T? butleri neonates, showed significant habituation of flight responses over the five tests. In T? butleri, but not T? melanogaster, males were more prone to attack than were females. In both species there were large differences in both overall strike scores and habituation rates of individual newborn animals. In Experiment 2, T? melanogaster 2-months old, were tested for short-term habituation to either a moving or nonmoving stimulus for 10 successive tests on one day. Habituation of strikes was similar to both stimuli, but more animals confronted with the moving stimulus showed an initial increase in strikes, lending support to the dual-process theory of habituation. As in Experiment 1, there were large individual differences in habituation rates. The results are discussed in terms of the ecological and methodological implications for developmental studies.