Overwinter ecology of Western Painted Turtles (Chrysemys Picta Bellii) in a Canadian reservoir

Overwintering is a critical life-history stage for species inhabiting temperate environments characterized by harsh, cold winters lasting up to half the year or longer. Ectotherms, such as herpetofauna, display behavioural adaptations in order to survive winters. During this period of their life history, those animals occupying fluctuating environments, such as reservoirs, may face additional challenges. I studied the overwinter ecology of a population of Western Painted Turtles (Chrysemys picta bellii) in a hydroelectric reservoir in British Columbia, Canada. My study built upon a preliminary study on the general ecology and population demographics of this population. This preliminary study identified variation in overwintering tactics between two water bodies within the reservoir – congregated and dispersive hibernation. The specific goals of my research were to (1) document more closely the variation in overwintering tactics occurring across the different subpopulations, (2) determine if the turtles in the subpopulations were experiencing and/or selecting different conditions during hibernation, and (3) determine if changes in reservoir levels during winter elicited response(s) in the turtles, and if so, examine how this relationship contributed to the use of different tactics. I focused on two locations within the reservoir that supported the overwhelming majority of turtles, and also included a small, isolated pond not influenced by the reservoir. By using radio telemetry to track turtles over two winters, my research identified variation in the overwintering tactics used between water bodies and years, and determined that overwintering tactics did not vary with water depth, temperature or dissolved oxygen. Turtles in all locations buried in the reservoir substrate for winter. Turtles displayed longer movements in winter than those documented in similar studies; however, these movements could not be correlated to changes in water levels. Body condition was comparable between the reservoir and reference water bodies yet population density and turtle size were notably higher in the non-reservoir location. In conclusion, this population of turtles exhibited behavioural plasticity in their overwintering tactics, and did not appear to be impacted by water level fluctuations in winter.