Thermal Responses in the Capercaillie Tetrao urogallus and the Black Grouse Lyrurus tetrix Roosting in the Snow

Abstract

Thermal responses were studied in the capercaillie and the black grouse roosting in closed snow burrows in northern Finland. For capercaillie, the air temperature within the burrow declined with the distance from the bird but was as high as 11 C adjacent to the bird when snow temperatures varied between -7.5 and - 11.5 C. The body temperature of the burrowed capercaillie was significantly lower than that of those roosting on the snow surface, indicating lessened alertness. In a comparison of the responses of the two species, the body temperature of burrowed black grouse was significantly higher than that of similarly situated capercaillie. The burrowed black grouse shivered occasionally but weakly during the night. Measurements of pectoral muscle electromyographic activity (EMG) were not taken for capercaillie. The results support the hypothesis that in winter, under suitable snow conditions, these birds are able to shelter in, or close to, a thermoneutral microenvironment.