The relationship between body and environmental temperatures in savanna elephants, Loxodonta africana

Abstract

As a result of climate change, environmental temperatures across southern Africa are predicted to rise by up to 5˚C by 2070. Elephants may be particularly vulnerable to these changes. Their small surface area to mass ratio and lack of sweat glands may impair heat loss. However, it is not known how elephants respond to high environmental temperatures (above 35˚C), limiting our ability to predict the responses of elephants to climate change. My study assessed these responses for the first time. Using an infrared thermal camera and ingestible thermometers, I recorded skin (at 10-minute intervals) and core temperature (at 5-minute intervals) in seven tame, free-ranging elephants. At the same time, I recorded environmental temperature (at 5-minute intervals) using a portable weather station. I expected skin temperature to increase with environmental temperature and to decrease when elephants moved into shade or wet their skin with mud or water. Because of these behavioural changes, I expected that core temperature would not increase with environmental temperature. I expected that if elephants use heterothermy, core temperature range would increase with environmental temperature range and maximum environmental temperature. I also expected that maximum core temperature would increase, and minimum core temperature would decrease with maximum environmental temperature. I found that skin temperature increased with environmental temperature (P<0.0001, generalized additive mixed model), and decreased when elephants were in shade (P<0.0001) or were wet (P<0.0001). Core temperature did not increase with environmental temperature (P=0.54), but increased with time of day (P<0.0001). Furthermore, core temperature range did not increase with environmental temperature range (𝛽=0.003, P=0.83, generalized linear mixed model) or maximum environmental temperature (𝛽=-0.01, P=0.59). Maximum core temperature did not increase (𝛽=0.01, P=0.45) and minimum core temperature did not decrease (𝛽=0.02, P=0.09) with maximum environmental temperature. I conclude that changes in behaviour, which decrease skin temperature, can assist elephants to maintain homeothermy. My findings show that in the heat, elephants maintain core temperature within a narrow range of 2˚C through behavioural changes, which reduce heat gain. I therefore suggest that elephants will be more likely to cope with the direct effects of climate change than not, provided shade and water are available.