Denning Ecology of Polar Bears in the Canadian Arctic Archipelago

From April 1989 through June 1992, we studied the denning ecology of 45 female polar bears in the Canadian Arctic archipelago, around M'Clure Strait and Viscount Melville Sound. Activity level of pregnant females was significantly lower in July-August compared to solitary, nonpregnant females. All maternity dens (n = 25) were located on land and were well dispersed throughout the study region. On average, females selected sites of maternity dens on 17 September and departed from dens on 21 March for a total den tenure of 186 ± 3 (SE) days. Middle-aged females left dens earliest, and young and old females had the longest den tenures. Activity level of females in maternity dens suggested that by 15 December most births already had occurred. Six of 20 nival shelters used by nonparturient females were located on the sea ice. In contrast to maternity dens, shelters were occupied for an average of only 53 ± 9 (SE) days, mainly from mid-December to late January. We hypothesize that shelters are used strictly for conserving energy during the coldest period of winter when conditions for hunting seals generally are unfavorable.