Polar Bears In Depth
Movements
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Data collected from radio-collared polar bears have confirmed their close ties to the ice. For example, between May 1985 and April 2001, we obtained 34,034 high-quality satellite radio-locations of polar bears in the Chukchi and Beaufort Sea areas of Alaska and northwestern Canada. Some collars had duty cycles that allowed them to transmit more frequently than other collars. When duty cycles were standardized so that each bear contributed one relocation per week, only 975 (7%) of 14,622 weekly locations were on land (Amstrup et al. 2000; Amstrup unpubl. data). Most of those were bears occupying maternal dens for the winter. In the polar basin area, polar bears truly are pelagic organisms (Garner et al. 1994)!
Telemetry data also have proven that polar bears do not wander aimlessly on the ice, nor are they carried passively with the ocean currents as previously thought (Pedersen 1945). Rather, they occupy multiannual activity areas outside of which they seldom venture. Annual activity areas of female polar bears monitored by radiotelemetry for multiyear periods varied among years. Collared animals, however, seemed to use seasonally preferred or "core" regions every year despite variation in annual activity area boundaries (Amstrup et al. 2000). This suggests that activity areas of polar bears, when viewed over multiyear periods, might be called home ranges. All areas of the home range, however, will not be used each year. Sea-ice habitat quality varies temporally as well as geographically (Stirling and Smith 1975; Ferguson et al. 1997, 1998, 2000a, 2000b; DeMaster et al. 1980; Amstrup et al. 2000). In areas of volatile ice, a large multiannual home range of which only a portion is used in any one season or year is an important part of the polar bear life history strategy.
Linear movements and activity areas are very large compared to those of most terrestrial mammals, and they vary in different regions of the globe, presumably because of variation in patterns of productivity and other sea-ice characteristics. In the Beaufort Sea, where polar bears have been followed by radiotelemetry for 20 years (Amstrup et al. 2000), total annual movements, calculated as the sum of straight-line distances separating consecutive weekly relocations, averaged 3415 km and ranged up to 6200 km. Movement rates of >4 km/hr were sometimes sustained for long periods, and movements of >50 km/day were observed. Annual activity areas of 75 radio-collared female polar bears in the Beaufort Sea region averaged 149,000 km2. The smallest annual activity area was nearly 13,000 km2, whereas the largest was 597,000 km2 (Amstrup et al. 2000).
Telemetry data also have proven that polar bears do not wander aimlessly on the ice, nor are they carried passively with the ocean currents as previously thought (Pedersen 1945). Rather, they occupy multiannual activity areas outside of which they seldom venture. Annual activity areas of female polar bears monitored by radiotelemetry for multiyear periods varied among years. Collared animals, however, seemed to use seasonally preferred or "core" regions every year despite variation in annual activity area boundaries (Amstrup et al. 2000). This suggests that activity areas of polar bears, when viewed over multiyear periods, might be called home ranges. All areas of the home range, however, will not be used each year. Sea-ice habitat quality varies temporally as well as geographically (Stirling and Smith 1975; Ferguson et al. 1997, 1998, 2000a, 2000b; DeMaster et al. 1980; Amstrup et al. 2000). In areas of volatile ice, a large multiannual home range of which only a portion is used in any one season or year is an important part of the polar bear life history strategy.
Linear movements and activity areas are very large compared to those of most terrestrial mammals, and they vary in different regions of the globe, presumably because of variation in patterns of productivity and other sea-ice characteristics. In the Beaufort Sea, where polar bears have been followed by radiotelemetry for 20 years (Amstrup et al. 2000), total annual movements, calculated as the sum of straight-line distances separating consecutive weekly relocations, averaged 3415 km and ranged up to 6200 km. Movement rates of >4 km/hr were sometimes sustained for long periods, and movements of >50 km/day were observed. Annual activity areas of 75 radio-collared female polar bears in the Beaufort Sea region averaged 149,000 km2. The smallest annual activity area was nearly 13,000 km2, whereas the largest was 597,000 km2 (Amstrup et al. 2000).