Thermoregulatory Behavior of the Northern Elephant Seal, Mirounga angustirostris

Observations on a colony of northern elephant seals on Guadalupe Island, Mexico, revealed that group patterns of sand flipping and migration to the surf were correlated with weather conditions. These behaviors were interrupted by a partial solar eclipse or by intermittent clouds. The occurrence of both behavioral patterns was essentially absent on overcast or rainy days. Sand flipping and wetting with water both create a favorable gradient for heat loss as shown by comparisons of temperatures at the skin surface. Wetting with sea water is the more effective in involving the largest surface for evaporative cooling. The efficacy of evaporative cooling is illustrated by an experiment in which periodic sprinkling of individuals with sea water prevented the behavioral sequence while it was occurring in un-wetted animals. Considerable thermolability, while on land, is indicated from telemetry data, which revealed a range in stomach temperature for two weanling seals of 35.7 to 39.1 and 37.2 to 39.6°C. The highest temperatures were associated with vigorous physical activity and exposure to direct sun (or both), whereas the lowest were recorded when individuals had been wetted at surfs edge or were relatively inactive and not exposed to intense sunlight. Sand flipping does not appear to occur at a specific deep-body temperature, but is most likely initiated through peripheral receptors sensitive to the rate of peripheral heating. While on land and under thermal loading from endogenous or exogenous sources, purely physiological mechanisms for heat dissipation (peripheral vasodilation, sweating, respiratory evaporative cooling) appear to be inadequate in maintaining a stable core temperature. On a clear day the behavioral sequence is typically: 1) exposure of the most reflective surface (belly up); 2) prone position followed by flipping of moist sand to the dorsum; and 3) migration to the edge of the surf where wetting and evaporative cooling occur. Elephant seals seem physiologically adapted to sea temperatures, their repertoire of purely physiological thermoregulatory mechanisms being insufficient to meet the thermal loads often encountered on land.