Thermoregulation in mule deer and elk

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Abstract
Thermoregulatory responses of mule deer (Odocoileus hemionus hemionus) and elk (Cervus elaphus nelsoni) were analyzed for air temperatures outdoors between 2 and 34 °C in summer and −38 and +24 °C in winter. Body temperatures differed between species, seasons, and ages. Surface skin temperatures varied with air temperature, incident radiation, and seasonal pelage. Respiratory rate and water loss increased exponentially while exhaled air temperatures varied sigmoidally as air temperature increased. Expired air volume increased logarithmically with increasing respiratory rate. Cutaneous evaporation (grams per square metre per hour) in summer was significantly greater in elk than in mule deer, which used panting as the primary means of heat dissipation in hot environments. Nonevaporative respiratory heat loss varied parabolically as a function of air temperature in both species. Thermally critical environments for mule deer occurred at operative temperatures of less than −20 °C and greater than 5 °C in winter and greater than 25 °C in summer. Energy expenditures increased for elk at operative temperatures below −20 °C and above +20 °C in winter, with metabolic rates decreasing between 10 and −20 °C. Maximum thermal resistances for mule deer and elk in winter were 1400 and 2000 s/m, respectively, compared with 600 and 400 s/m in summer.