Thermal Ecology of Spotted Turtles (Clemmys guttata) in Two Southern Populations

The ecology of many ectotherms depends heavily on their ability to navigate the surrounding thermal environment in a manner that maintains body temperature (T_b) within or near some optimal temperature range at least some of the time. From April–December 2016, we measured shell temperatures (T_s) and water temperatures (T_w) in two Spotted Turtle (Clemmys guttata) populations in southeastern Georgia using iButton temperature loggers. We attached radio transmitters and iButtons to the carapace of adult Spotted Turtles (n = 18 and 11 in each population, respectively) in early spring. Temperature loggers recorded a T_s measurement every 90 minutes (accuracy = 0.5°C), and we restricted our analyses to temperatures recorded between sunrise and sunset. Monthly mean T_s ranged from 12.3±3.4 to 27.1±2.7°C (SD), and seasonal variation accounted for a majority of the observed variation in temperatures. We found a strong positive correlation between weekly mean T_s and weekly mean T_w at one site that remained flooded throughout the study (P < 0.0001, R² = 0.99). T_w could not be measured at the other site because it dried completely early in the study. Spotted Turtles did occasionally (<5% of total temperature observations) bask to raise T_s above that of the surrounding T_w. Gravid females achieved significantly higher daily maximum temperatures (26.2°C) than males (24.5°C) during the four weeks surrounding egg development (P = 0.043). In general, Spotted Turtles at the southern end of their range appear to spend a majority of their time conforming to environmental temperatures that often fall within the preferred range for the species.