Effects of heat, cold, and rain on coastal black-tailed deer

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Abstract
Thermoregulatory responses of black-tailed deer (Odocoileus hemionus columbianus) were recorded in a metabolic chamber at dry air temperatures between −20 and 32 °C. For animals in summer pelage, respiratory rates, body core temperatures, and skin temperatures increased curvilinearly with increasing air temperature; thermally critical air temperatures occurred above 27 °C and below 10 °C. In winter, body temperatures were lower in adults than in fawns, skin temperatures were highly variable, and respiratory rates increased at lower air temperatures than in summer; metabolic expenditures associated with thermoregulation increased at temperatures less than −10 °C. Animals were also subjected to simulated rain (4.5 mm/h) over a 5-h period at temperatures above freezing. During summer trials in the rain, body and skin temperatures generally declined after 5 h. No increased metabolic stress associated with rain was observed for black-tailed deer in summer at air temperatures greater than 12 °C; at 10 °C, energy expenditures after 5 h of rainfall were greater than during heat or cold stress. For animals in winter pelage, changes in body temperature, skin temperature, and hair depth showed no consistent trends with duration of rainfall; only fawns increased metabolism at temperatures just above freezing (2–3 °C) in the rain. Data from this study suggest that rainfall may pose major energetic constraints for black-tailed deer in summer pelage. Managerial provisions for thermal cover should place highest emphasis on summer habitats.