The influence of season, temperature, and absorptive state on sage grouse metabolism

Abstract

We used indirect respiration calorimetry to measure the metabolism of six adult sage grouse (Centrocercus urophasianus) during winter, spring, and summer. During winter the metabolic rate of fed birds was higher (P < 0.05) than that of fasted birds. The standard metabolic rate (SMR) of females (0.692 mL O2∙g−1∙h−1) was higher than of males (0.583 mL O2∙g−1∙h−1) in winter; in both sexes SMR was higher in winter than in summer. Females' SMR was lower (P = 0.0001) in spring than in winter. Lower critical temperatures of both males and females were substantially lower in winter (−0.6 °C, −4.8 °C) than in summer (14.9 °C, 14.8 °C). Although seasonally elevated, the SMR of sage grouse in winter is low in comparison with that of other galliforms with northern distributions. Thermoregulation during a winter night at −10 °C would result in minimal (<5%) expenditure of endogenous reserves by either sex. Thermoregulation and SMR in winter are more energetically costly to female sage grouse than to males, and may necessitate increased behavioral thermoregulation by females. Seasonal change in SMR differs between the sexes, and is probably influenced by the energetic demands of the breeding season.