Minimal overwintering temperatures of red-sided garter snakes (Thamnophis sirtalis parietalis): a possible cue for emergence?

• Published in: Canadian journal of zoology Vol. 84; no. 5; pp. 771 - 777
• Main Authors: Lutterschmidt, Deborah I, LeMaster, Michael P, Mason, Robert T
• Format: Journal Article
• Language: English
• Published: Ottawa, ON National Research Council of Canada 01.05.2006; NRC Research Press; Canadian Science Publishing NRC Research Press
• Subjects: Animal behavior; Animal reproduction; Biological and medical sciences; Body temperature; Fundamental and applied biological sciences. Psychology; Garter snakes; Low temperature; Overwintering; Physiological aspects; Snakes; Spring; Temperature; Thermoregulation. Hibernation. Estivation. Ecophysiology and environmental effects; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Winter; Canada; Thamnophis sirtalis; Vertebrata; Circannual rhythm; Overwintering; Body temperature; Emergence; Minimum temperature; Reptilia; Ophidia
• ISSN: 0008-4301; 1480-3283; 1480-3283; 0008-4301
• DOI: 10.1139/z06-043

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 red-sided 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 °C, mean ± SE) to early April (1.1 ± 0.16 °C, mean ± SE) during winter dormancy, reaching minimal values approximately 1 month prior to spring emergence. Body temperatures of emerging snakes ranged from 0.5 °C during early spring to 6.3 °C during late spring (3.4 ± 0.84 °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 °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.