Department of Integrative Biology

Red-sided garter snakes (Thamnophis sirtalis parietalis (Say in James, 1823)) in Manitoba, Canada, undergo 8 months of continuous winter dormancy prior to spring emergence. As in other ectothermic species, increases in ground temperature may be the cue for emergence from winter dormancy in these populations. To test this hypothesis, we measured body temperatures during winter dormancy by surgically implanting small temperature loggers into 32 female redsided garter snakes before they entered their native hibernaculum. The following spring, we recaptured seven of the snakes implanted with temperature loggers. Body temperature declined gradually from mid-September (14.7 +/- 0.24 degrees C, mean SE) to early April (1.1 +/- 0.16 degrees C, mean SE) during winter dormancy, reaching minimal values approximately I month prior to spring emergence. Body temperatures of emerging snakes ranged from 0.5 degrees C during early spring to 6.3 degrees C during late spring (3.4 +/- 0.84 degrees C, mean SE). These results do not support the hypothesis that an increase in ground temperature (and hence body temperature) is necessary for emergence from winter dormancy. We suggest that critically low temperatures (i.e., 0.5-1 degrees C) are a Zeitgeber entraining an endogenous circannual cycle that regulates snake emergence. These results offer new insight into the mechanisms regulating seasonal emergence from winter dormancy.