SEASONAL PATTERNS OF BODY-TEMPERATURE AND ACTIVITY IN FREE-RANGING BEAVER (CASTOR-CANADENSIS)

Daily activity and body temperature patterns of beavers (Castor canadensis) were monitored in the field with an automated radiotelemetry system from June 1988 through March 1989. Body temperatures of kits and adults averaged close to 37-degrees-C throughout the year, with no evidence of seasonal hypothermia. The greatest temperature changes accompanied episodes of aquatic activity. Body temperature typically dropped 1.0-1.5-degrees-C during periods when beavers were absent from the lodge, then recovered when animals returned to the house. Throughout the open-water season (20 June - 1 November), both age groups demonstrated a daily rhythm in body temperature characterized by a gradual rise between 06:00 and 18:00 followed by a general decline during the nocturnal active period. During the ice-bound season (2 November - 15 March), there was little evidence of a distinct daily rhythm in activity or body temperature, especially in adults. Both age groups exhibited a 0.22-0.64-degrees-C increase in mean body temperature during the 3-h period preceding the first trip in each sequence of excursions away from the lodge. We propose that this predeparture rise in temperature may contribute to the avoidance of immersion hypothermia in foraging beavers.