Overwintering ecology of Wood Turtles (Glyptemys insculpta) at the species' northern range limit

摘要

Seasonal variation in activity patterns of reptiles is accompanied by physiological and behavioral adjustments that influence their ecology and life history, and overwinter survival may be an important factor limiting a species' northern range extension. A northern population of Wood Turtles (Glyptemys insculpta) in Ontario, Canada was surveyed in fall 2004, and a subset of adults was radio-tracked every 7-12 days during the winter of 2004-2005 to examine thermal aspects of overwintering. We predicted that Wood Turtles would use hibernacula that protect them from freezing and predation. Temperature data loggers indicated that turtle body temperatures and hibernacula temperatures remained near 0 degrees C from 2 December 2004 until 3 April 2005. During the same period, air temperatures fluctuated substantially and reached a maximum of 10.5 degrees C (on 30 March 2005) and a minimum of less than -40 degrees C (on 21 January 2005) with a mean of -8.3 degrees C. Turtles did not select specific water temperatures nor did they use distinct structures (e.g., root hollows, logjams, and holes in the riverbank) for overwintering but instead rested relatively exposed on the riverbed at a depth of approximately 1 m and at a mean distance of 1.0 m from the riverbank. Surprisingly, turtles made small movements during winter (0.1-10.0 m between radiolocations), typically against the river current and in a direction parallel to the riverbank. Average winter home-range size was 7.1 m(2). Our findings raise questions about why turtles move during winter, we suggest possible answers and future lines of investigation to address these questions.