Most Holarctic bears of the genus Ursus enter a metabolically dormant state each winter during which they undertake an extended fast (Nelson, 1980). For most of the dormant period, individual bears ensconce themselves in a sheltered den, the construction of which varies greatly depending on the species, habitat, and general winter conditions (Johnson and Pelton, 1980; Lentz et al., 1983). Although over-winter dens are critical for bears, reuse of individual dens is rare, at least in the American black bear (U. americanus), suggesting that suitable sites for dens are not limiting (Alt, 1984; Tietje and Ruff, 1980).
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