Temperature regulation responses of ornate box turtles, Terrapene ornata, to heat

Abstract

1. 1. Eleven ornate box turtles after being preheated to 30°C core temperature were exposed to 38,41,43·3,48 and 51°C experimental environments to assess their ability to thermoregulate. 2. 2. Exposure to 38 and 41°C was not a heat stress for these turtles as evidenced by absence of restless activity, very little evaporative weight loss, no frothing and no change in heart rate. 3. 3. Frothing was adopted as an indicator of maximum physiological thermoregulation because after frothing commenced, core to air temperature gradients were established. Core to air gradients were larger in the hotter environments and onset of frothing began earlier during the heat exposure. At 48°C an 8·5°C core to air gradient was maintained for 3 hr and at 51°C a 10·5°C core to air gradient was maintained for 1·5 hr. 4. 4. Increased heart rate and evaporation of saliva and urine were effective responses which accompanied thermal balance. Weight loss appears to be a much better index of thermal stress than is heart rate.