Development of antipredator responses in snakes: V. Species differences in ontogenetic trajectories.

The ontogeny of antipredator responses in five species of Natricine snakes was examined. In a split-litter experiment, neonates were given a standardized defensive behavior test at 1 and/or 20 days of age. Thamnophis sirtalis and Thamnophis melanogaster showed a significant increase in both striking and fleeing from a threatening stimulus. Thamnophis butleri was not reactive in terms of striking at either age but did flee frequently at both ages. Thamnophis radix showed low rates of striking and high rates of fleeing; only fleeing increased significantly between the two tests. Nerodia rhombifer exhibited moderate rates of both striking and fleeing at both ages with no developmental effects. Subsets of most of these species tested at 40 or 60 days of age found no further developmental changes.