LUTTERSCHMIDT, D.I.*; LEMASTER, M.P.; MASON, R.T.; Oregon State Univ., Corvallis; Western Oregon Univ., Monmouth; Oregon State Univ., Corvallis: Minimal over-wintering temperatures of red-sided garter snakes: A possible cue for emergence?

Red-sided garter snakes (Thamnophis sirtalis parietalis) in Manitoba, Canada inhabit the northernmost limit of this species� range. Beginning in May, snakes emerge from hibernacula after 8 months of winter dormancy. Given the unique life history of this species, temperature is likely the most important proximate environmental cue governing the initiation of emergence and mating behavior. It is suggested that gradual increases in ground temperature are the cue for emergence from winter dormancy in this species. To test this hypothesis, we measured body temperatures (T_b) during winter dormancy by surgically implanting small temperature-loggers into female snakes. Surgeries were conducted in the fall when snakes were returning to the hibernacula. Snakes were then released and allowed to hibernate under natural conditions. The following spring, we recaptured 7 of 32 implanted snakes. Although T_b declined steadily from 15 to 1 C over the 8-month dormancy period, T_b did not reach minimal levels until early April, only 1 month before spring emergence. Mean T_b just prior to emergence was 4 C. Thus, these results do not support the hypothesis that a gradual increase in T_b triggers emergence from winter dormancy. An increase in T_b still may be a cue for emergence, but the underlying mechanism must be sensitive to small changes in T_b (i.e., 3 C) over a short period of time (i.e., 1 month). Alternatively, critically low temperatures (i.e., 1 C) may stimulate snake emergence. These results are the first records of T_b for red-sided garter snakes in natural hibernacula and offer new insight into the mechanisms regulating seasonal emergence from winter dormancy.