Taking the heat: thermoregulation in Asian elephants under different climatic conditions.

Some mammals indigenous to desert environments, such as camels, cope with high heat load by tolerating an increase in body temperature (T (b)) during the hot day, and by dissipating excess heat during the cooler night hours, i.e., heterothermy. Because diurnal heat storage mechanisms should be favoured by large body size, we investigated whether this response also exists in Asian elephants when exposed to warm environmental conditions of their natural habitat. We compared daily cycles of intestinal T (b) of 11 adult Asian elephants living under natural ambient temperatures (T (a)) in Thailand (mean T (a) ~ 30°C) and in 6 Asian elephants exposed to cooler conditions (mean T (a) ~ 21°C) in Germany. Elephants in Thailand had mean daily ranges of T (b) oscillations (1.15°C) that were significantly larger than in animals kept in Germany (0.51°C). This was due to both increased maximum T (b) during the day and decreased minimum T (b) at late night. Elephant's minimum T (b) lowered daily as T (a) increased and hence entered the day with a thermal reserve for additional heat storage, very similar to arid-zone ungulates. We conclude that these responses show all characteristics of heterothermy, and that this thermoregulatory strategy is not restricted to desert mammals, but is also employed by Asian elephants.