Physiological thermoregulation in the spurred tortoise (Testudo graeca L.)

Summary

Evaporative cooling, through moistening of the eyes, panting, urinating and salivating, takes place in the spurred tortoise at high ambient temperatures. The mean temperature at which thermoregulatory salivation is initiated (39·5° ± 0·4°C) is constant, irrespective of body size, but the rate of panting is slower in heavier tortoises. Very small tortoises, however, do not pant for more than a few seconds.

Tortoises are inactive at 13°C and their body temperatures do not vary from the ambient. At 21° and 26°C, heat loss through transpiration exceeds metabolic heat production: at 33°C body temperatures are higher than the ambient. Increased range and variability at higher temperatures may be explained by the fact that spurred tortoises hold their breaths for long periods—a mechanism that could serve to reduce respiratory water loss. When breathing is actually taking place, however, the rate of respiration depends on body temperature: this grades into panting above 35°C.