Microhabitat and prey odor selection in the foraging pigmy rattlesnake

We tested the roles of shelter and prey odor cues on the prestrike movement patterns of the dusky piginy rattlesnake, Sistrurus miliarius barbouri. In the first experiment, prey odors-mouse, frog, lizard, plus control-were presented in various combinations with and without shelters. The pigmy rattlesnake initially preferred sites with both from odor and shelter. However, this changed over a 23-h period so that shelter alone became the most preferred feature of the microhabitat choices. The initial 2 h pigmy response was similar to that reported for the western rattlesnake (Crotalus viridius), in that they responded differently to the four choice combinations of shelter and prey odor. This initial pigmy response differed in that only frog odor (but not mouse or lizard odor) affected their initial choices. Our work also indicates that when foraging. novel prey odors (frog) initially attracted their attention, but preference for this odor soon declined. In the second experiment, we examined the preference for prey odors by simultaneously presenting all three prey odors plus control (water). The snakes exhibited no prey odor preference during the first 2-h or during the total 23-h of the trials. In both experiments, the pattern of circadian activity was the same. Circadian activity showed two peaks, one shortly before onset of the nocturnal phase and the second just before midnight: thereafter, activity gradually declined so that most snakes were in, and remained in, a shelter by morning when the diurnal phase began. In these experiments, active movement in pigmy rattlesnakes occurred nocturnally and by day they remain in settled locations. While in such settled positions, the pigmy rattlesnakes coiled into stereotypic ambush postures facing the opening in their shelter where prey would most likely pass.