Summer and Winter Temperature Regulation in the Black Grouse Lyrurus tetrix

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Abstract
Metabolic rate and thermal responses to ambient temperatures between -26.5 C and 34.0 C were studied in the adult black grouse in both summer and winter, and in juvenile (70-80 days old) black grouse in early autumn. At an ambient temperature between 0 C and 20 C, the body temperature of the adult grouse was significantly higher in summer (41.3 ± .09 C) than in winter (40.2 ± .14 C). The standard metabolism at thermoneutrality was 6.5 W/kg in summer and 8.2 W/kg in winter, being higher in both seasons than predicted by theoretical equations. The lower critical temperature was 9.5-12.5 C in summer and around 5 C in winter. However, no clear inflection point was seen in the metabolism in winter. The increase in metabolic rate was only 1.7-fold in winter and 2.2-fold in summer when ambient temperature decreased from 30 C to -23 C. At ambient temperatures ranging from 10 C to -23 C the thermal conductance was higher in winter than in summer; in winter, but not in summer, it decreased with decreasing ambient temperature. The assumption is that in winter the black grouse improve their insulation also at ambient temperature far below the lower critical temperature.