Spring Emergence Patterns of Wandering Garter Snakes and Prairie Rattlesnakes in Wyoming

Although intraspecific and interspecific variation in dates of spring emergence is known among snakes, factors affecting such variation are not. Dates of spring emergence from hibernation were recorded for individual wandering garter snakes (Thamnophis elegans vagrans) and prairie rattlesnakes (Crotalus viridis) in south-central Wyoming. Due to differing seasons of mating and mating systems of these species, we predicted that male garter snakes, but not male rattlesnakes, would emerge prior to conspecific females. Garter snakes emerged earlier than rattlesnakes, and male garter snakes emerged earlier than conspecific females. Male garter snakes remained near hibernacula where vernal courtship with emerging females was observed frequently. In contrast, spring courtship was never observed among rattlesnakes, and there was no difference between dates of spring emergence of males and females. Thus, predictions concerning associations between emergence patterns and mating systems were supported.