Thermoregulation as a function of thermal quality in a northern population of painted turtles, Chrysemys picta

Body temperature affects nearly all processes of ectotherms. Reptiles do not generate sufficient body heat to regulate their body temperature internally and therefore use behavioural thermoregulation. We determined whether thermoregulatory effort varied among seasons in an environment where large temporal differences in environmental temperatures (T_e) exist. We took 31 297 internal body temperature (T_b) measurements from 18 painted turtles (Chrysemys picta(Schneider, 1783)) throughout their active season. We estimated T_e with physical models and water temperatures. We measured the range of preferred body temperatures (T_set) in a thermal gradient. T_set was 21.3–25.0 °C. We used T_b, T_e, and T_set to calculate standard thermoregulation indices (E_x and d_e – d_b). An E_x of 40.7% and a d_e – d_b of 2.4 °C indicated that painted turtles are moderate thermoregulators, despite inhabiting a high-cost environment. Effort to regulate T_bincreased as the thermal quality of the habitat decreased. Thermoregulatory effort was higher when T_set could not be achieved. Painted turtles put more effort in thermoregulation in the early season than in the rest of the season. This within-species pattern follows the pattern seen among species. This study is the first to measure T_b internally and to apply standard thermoregulation indices to free-ranging turtles.