Thermoregulation in a North Temperate Population of Midland Painted Turtles (Chrysemys picta marginata): Temporal Patterns and Intersexual Differences

The regulation of body temperature (Tb) is important for energy acquisition in ectotherms but may be challenging and costly. We studied the thermal biology of a north temperate population of Midland Painted Turtles (Chrysemys picta marginata) in a small pond in central Michigan. Cycling of mean daily body temperature (T-b) began as early as March and continued through October. The thermoregulatory setpoint range was 25-31 degrees C, and turtles largely maintained Tb near or within the T-set range throughout the day between May and September. Mean hourly Tb was slightly (+0.5 degrees C) higher on sunny days when compared to cloudy days. Turtles had relatively low investment in thermoregulation during the fall months potentially as an energy conservation measure prior to hibernation. Thermal exploitation values (E-x) indicated that our turtles spent as much, or more, time within the T-set range than individuals in other north temperate Painted Turtle populations and other reptile species studied to date, which was most likely due to the relatively high thermal quality of our aquatic environment. We did not find differences between males and females in terms of thermal exploitation, which suggests little or no differences in thermal energy needs that might be associated with potential energetic allocations to reproductive activities (e.g., ovarian development or mate location in males).