Savanna elephants maintain homeothermy under African heat

Abstract

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.

Air temperature and diet influence body composition and water turnover in zoo-living African elephants (Loxodonta africana)

“…We used air temperature as a crude estimate of ambient temperature that elephants experience in shaded locations. Studies conducted on African elephants in southern Africa found that air temperature measurements track black globe temperatures, which provide an integrated measure of air temperature, radiant temperature and the cooling effect of wind [ 39 , 40 ]. We calculated average maximum, minimum and mean air temperature for each 10 day measurement period using readings of daily maximum, minimum and mean air temperature.…”

Obligatory Nocturnalism in Triassic Archaic Mammals: Preservation of Sperm Quality?

“…Elephants have giant, well-vascularized ears that are flapped at high temperatures to dissipate heat. They are testicond, and African elephants (Loxodonta africana) have T b ≈ 36:67C (Mole et al 2018). They are completely dependent on water for thermoregulation, even desert-dwelling populations (Viljoen1988;Viljoen and du P. Bothma 1990), to avoid hyperthermia when T a exceeds T b (Mole et al 2018).…”

“…They are testicond, and African elephants (Loxodonta africana) have T b ≈ 36:67C (Mole et al 2018). They are completely dependent on water for thermoregulation, even desert-dwelling populations (Viljoen1988;Viljoen and du P. Bothma 1990), to avoid hyperthermia when T a exceeds T b (Mole et al 2018). Specialized behavior involves bathing in mud, spraying water on skin (Mole et al 2018), and resting in shade during the heat of the day.…”

“…They are completely dependent on water for thermoregulation, even desert-dwelling populations (Viljoen1988;Viljoen and du P. Bothma 1990), to avoid hyperthermia when T a exceeds T b (Mole et al 2018). Specialized behavior involves bathing in mud, spraying water on skin (Mole et al 2018), and resting in shade during the heat of the day. Their extremely large body size, together with their heat-dissipating adaptations, ensures that African elephants do not employ heterothermy, that is, the storage of heat, to minimize water requirements (Mole et al 2018).…”

“…Specialized behavior involves bathing in mud, spraying water on skin (Mole et al 2018), and resting in shade during the heat of the day. Their extremely large body size, together with their heat-dissipating adaptations, ensures that African elephants do not employ heterothermy, that is, the storage of heat, to minimize water requirements (Mole et al 2018). The dicynodonts did not persist into the Jurassic, and given their relative rarity in an otherwise rich therapsid fossil record, a largebodied, nonnocturnal Late Triassic therapsid such as L. bojani did not possess an evolutionary successful Bauplan.…”