Movements and behavior of migratory garter snakes, Thamnophis sirtalis

Abstract

Although garter snake populations in northern areas have been shown to undergo annual migrations, no detailed information has been available on these movements. Through biotelemetry and, to a lesser extent, mark–recapture methods, the migration of an extreme northern population of Thamnophis sirtalis was documented. Snakes emerging from a hibernaculum moved towards the closest freshwater marsh, which was approximately 3.75 km away. Radio-tracked individuals moved along a constant bearing; once they reached the proximal regions of the marsh, they continued to move away from the den, but circled back during the later part of the summer. One individual completed a round trip of over 15 km during one active season. Snakes routinely exhibited a distinct behavioral sequence during the daily travels, and five rather lengthy searches for overnight retreats were observed. The extensive migration documented in this study may be quite costly for the northern snakes, for (i) it may significantly decrease the time available for other important activities, such as feeding, and (ii) it increases the snakes' exposure to the adverse spring and fall weather conditions, which in turn may subject them to predation or lethal temperatures.