The mating season is a time of great exertion for male elephant seals. Defending their harem, the males fast and lose approximately 36% of their body mass during their mating marathon. Not surprisingly, the well-insulated animals generate colossal amounts of heat during their exertions, but lacking sweat glands, elephant seals can only lose excess heat by directing blood to the skin to radiate away. Knowing that elephant seals can selectively raise the temperature of patches of skin to prevent themselves from over heating, Amy Norris, with colleagues from Sonoma State University, wondered what effect environmental and behavioural factors had on the skin temperatures of elephant seal males during this extreme endurance test (p. 4205).

Travelling to the Año Nuevo Reserve, California, Norris, Dorian Houser and Dan Crocker filmed male elephant seals with a thermographic camera over the 3 month mating season. Recording thermal images of the animals during combat and other routine activities, the team collected over 2550 images from 82 males ranking from dominant alphas down to peripheral males. Analysing the animals' heat distributions, Norris and her colleagues found that solar radiation, vapour pressure and the month all significantly affected the animals' surface temperatures, with the surface temperatures of some animals rocketing to 30°C on the sunniest days while cooling to 15°C on overcast days. The team also found that battling males had the largest thermal windows, where the skin temperature is one standard deviation above the animal's mean temperature, to help them lose heat. However, the competing males were not the hottest: the most inactive males had the highest surface temperatures and largest temperature gradients between themselves and the environment. The team suspects that on warm and humid days, when it is more difficult to dump excess heat, the males limit their activity levels to prevent themselves from over heating. ‘These results strongly suggest males modify behaviour relative to the potential for convective or evaporative heat loss,’ the team says.

A. L.
D. S.
D. E.
Environment and activity affect skin temperature in breeding adult male elephant seals (Mirounga angustirostris)
J. Exp. Biol.