The distribution of polar bears (Ursus maritimus) is circumpolar in the Northern Hemisphere, but known locations of maternal dens are concentrated in relatively few, widely scattered locations. Denning is either uncommon or unknown within gaps between known denning concentration areas. The Beaufort Sea region of Alaska and Canada lies in the largest of those gaps. To understand effects of industrial development and proposed increases in hunting, the temporal and spatial distribution of denning in the Beaufort Sea must be known. We captured and radiocollared polar bears between 1981 and 1991 and determined that denning in the Beaufort Sea region was sufficient to account for the estimated population there. Of 90 dens, 48 were on drifting pack ice, 38 on land, and 4 on land-fast ice. The proportion of dens on land was higher (P = 0.029) in later compared with earlier years of the study. Bears denning on pack ice drifted as far as 997 km (xBAR = 385 km) while in dens. There was no difference in cub production by bears denning on land and pack ice (P = 0.66). Mean entry and exit dates were 11 November and 5 April for land dens and 22 November and 26 March for pack-ice dens. Female polar bears captured in the Beaufort Sea appeared to be isolated from those caught east of Cape Bathurst in Canada. Of 35 polar bears that denned along the mainland coast of Alaska and Canada 80% denned between 137-degrees-00'W and 146-degrees-59'W. Bears followed to > 1 den did not reuse sites and consecutive dens were 20-1,304 km apart. However, radio-collared bears were largely faithful to substrate (pack-ice, land, and land-fast ice) and the general geographic area of previous dens. Bears denning on land may be vulnerable to human activities such as hunting and industrial development. However, predictable denning chronology and lack of site fidelity indicate that many potential impacts on denning polar bears could be mitigated.
