| Summary: | Our study tested the hypothesis that the Northern elephant seal (NES) Mirounga angustirostris uses coloration for thermoregulation on land. The NES comes ashore every winter to breed and—being adapted to living in cold seas for most of the year—on shore they may be faced with over-heating from higher temperatures and direct solar radiation. Their large size and thick blubber give adult NES’s low surface area to volume ratios and a layer of thermal insulation which are advantageous for conserving heat in cold seas but disadvantageous for dissipating it on land. However, they are very dark on the back and pale beneath, which could allow them to absorb or reflect heat by adjusting orientation to the sun. Pups are born with no blubber but are uniformly black, which could allow them to absorb heat from the sun over the entire body surface. We found that pups did tend to stay exposed to sunlight in cooler hours and shaded by their mothers’ shadows in warmer ones. In adults we found that females exposed their reflective bellies to the sun more than males at all times and that both sexes were significantly more likely to orient the belly toward the sun during warmer hours compared to cooler ones.
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