Chemical, thermal, and physical properties of sites selected for overwintering by northern wood turtles (Glyptemys insculpta)

Abstract

Northern ectotherms must seek refuge from winter conditions for a large portion of their annual activity cycle. The objective of this study was to quantify physical properties of overwintering sites selected by wood turtles ( Glyptemys insculpta (LaConte, 1830)) at the species’ northern range limit. We mapped all structural features (e.g., root balls and log jams), water depth, and sediment types along a 1.5 km stretch of river that was available to turtles outfitted with radio transmitters (N = 8) during winter. Temperature selection was assessed by comparing thermal profiles from data loggers on turtles and temperature stations within the river and other riparian habitats (e.g., ephemeral pools and oxbows). Dissolved oxygen (DO) was measured at each temperature station and turtle location. Wood turtles overwintered in the river, which was colder (~0 °C), had more stable temperatures, and provided higher DO (12.64 ppm) compared with adjacent habitats. Some turtles selected structured refuges for overwintering. Winter movements were not related to temperature or DO, but may be related to maintaining a certain distance from shore and water depth to protect against accidental relocations during winter. We discuss hibernacula as potential factors limiting the northern distribution of wood turtles, a species at risk in Canada.