Rattlesnake predatory behaviour: mediation of prey discrimination and release of swallowing by cues arising from envenomated mice.

Abstract Responses of rattlesnakes to envenomated mice were examined in five experiments. In experiment 1 rattlesnakes ( Crotalus durissus terrificus and C. viridis viridis ) discriminated mice that they had envenomated, as indexed by number of tongue flicks and accumulated investigation time, when these prey items were paired with control mice killed by the experimenter. Experiment 2 demonstrated that rattlesnakes also exhibited this discrimination when presented with mice envenomated by a conspecific and controls killed by the experimenter. In experiments 1 and 2, we observed that rattlesnakes delivered a large number of tongue flicks to exudates associated with nasal-oral tissues of envenomated mice. It has commonly been noted that rattlesnakes typically swallow envenomated, dead mice head first. In experiment 3 this observation was statistically verified. Evidence obtained in experiment 4 indicated that nasal-oral tissues of envenomated, dead mice were discriminated from anogenital tissues by rattlesnakes. Cues arising from the nasal-oral tissues probably (1) assisted the snakes in locating the head-end of the rodent, and (2) released the swallowing modal-action pattern, the final phase of the predatory sequence. In experiment 5, rattlesnakes exhibited no discrimination between nasal-oral and anogenital tissues of non-envenomated, dead mice, indicating that the results of experiment 4 were probably dependent upon effects of envenomation.