Meeting Abstract
98.8 Thursday, Jan. 7 Are Elephants Obligate Evaporative Coolers? DUNKIN, R.*; WILLIAMS, T.; WILSON, D.; JOHNSON, S.; JOHNSON, K.; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz; Wildlife Safari; Six Flags, Vallejo; Have Trunk Will Travel dunkin@biology.ucsc.edu
Elephants often occupy habitats with sustained high temperatures and low water availability, however, patterns of habitat use suggest they are highly water dependent. Although they lack sweat glands, relatively high rates of evaporative water loss (EWL) have been measured from elephant ears and EWL appears important for heat dissipation. However, it is unknown whether elephants are obligated to use evaporative cooling to maintain thermal balance nor whether they can mitigate water loss through behavioral or physiological mechanisms. We measured heat production and heat loss for 6 African and 6 Asian elephants across ambient temperatures (Ta) between 9 and 33°C and after animals were bathed. Skin temperatures, heat flux, and transdermal EWL were measured at 5 body sites and digital images were used to calculate body surface area. Metabolic heat production and respiratory evaporative water loss were measured simultaneously using open flow respirometry. We then modeled heat balance as a function of Ta. We found for both species the temperature gradient between the skin and environment approached 0°C at Ta between 25 and 28°C, corresponding to heat flux near 0 W m-2. Between 9 and 33°C, non-evaporative heat dissipation accounted for 160 to -20% of resting metabolic heat production (mean ±SD = 1875.8 ± 354.5W). Evaporative cooling increased heat dissipation between 20 and 48% from dry skin and 33 to 105% from wet skin. Evaporative cooling appears essential for heat dissipation above Ta between 28-33°C and during exercise. Elephants do not appear able to reduce EWL and instead rely on mud bathing to mitigate endogenous water loss. Obligate evaporative cooling likely explains elephant water dependence and may represent a liability during drought conditions and with increasing desertification.
