Savanna elephants maintain homeothermy under African heat.

To conserve body water, mammals may reduce evaporative water loss by storing heat, allowing core body temperature to rise more than usual during the day, and to fall more than usual during the cooler night, so demonstrating heterothermy. It has been proposed that elephants are heterothermic, but body temperature never has been measured in elephants over 24 h at environmental temperatures higher than body temperature, where elephants would have to rely on evaporative cooling to maintain homeothermy. We used ingested temperature data loggers to record core temperature of four partly free-ranging savanna elephants exposed to high solar radiation and environmental temperatures that exceeded core temperature (> 36 °C) in their natural habitat. The elephants maintained core temperature at an average 36.6 °C within narrow daily limits of about 1.3 °C. While mean 24-h core temperature increased with maximum air temperature, it did not increase with mean air temperature. Maximum and minimum daily core temperatures also did not change with maximum air temperatures. As a result, core temperature range remained constant despite large variations in daily air temperatures. Contrary to the view that elephants exhibit heterothermy to cope with heat, savanna elephants in their natural habitat with access to adequate resources of food and water, and able to use thermoregulatory behaviour, maintained homeothermy.

Coping with heat: behavioural and physiological responses of savanna elephants in their natural habitat.

Most of southern Africa's elephants inhabit environments where environmental temperatures exceed body temperature, but we do not know how elephants respond to such environments. We evaluated the relationships between apparent thermoregulatory behaviour and environmental, skin and core temperatures for tame savanna elephants (Loxodonta africana) that were free-ranging in the hot parts of the day, in their natural environment. Environmental temperature dictated elephant behaviour within a day, with potential consequences for fine-scale habitat selection, space use and foraging. At black globe temperatures of ~30°C, elephants adjusted their behaviour to reduce environmental heat load and increase heat dissipation (e.g. shade use, wetting behaviour). Resting, walking and feeding were also influenced by environmental temperature. By relying on behavioural and autonomic adjustments, the elephants maintained homeothermy, even at environmental temperatures exceeding 40°C. Elephants clearly have the capacity to deal with extreme heat, at least in environments with adequate resources of forage, water and shade. Future conservation actions should provide for the thermoregulatory, resource and spatial needs of elephants.