Winter Activity Patterns of Two Radio-Marked Beaver Colonies

Abstract

Activities of two radio-marked beaver (Castor canadensis) colonies were studied during the winters of 1976–1977 and 1977–1978. In one colony the adult male and adult female displayed free-running activity rhythms of 29.0 and 26.6 h respectively, under variable ambient temperatures and intermittent ice cover. Their activities were asynchronous for a period when the adult male apparently was entrained to a weak photoperiod Zeitgeber, and the adult female was free-running. For both colonies an index of above-ice activity was positively related to ambient temperature, i.e., below about −10°C above-ice activity was absent and, as temperature increased, above-ice activity increased. Free-running activity patterns and above-ice activity are interpreted to be behavioral adaptations related to wintertime bioenergetic budgets.