Distribution of polar bears (Ursus maritimus) during the ice-free period in western Hudson Bay

Abstract

The distribution and movements of polar bears (Ursus maritimus) during the ice-free period in western Hudson Bay were studied using mark and recapture and radiotelemetry locating of animals of known age and sex collected between 1966 and 1987. Polar bears segregated themselves by age, sex, and reproductive status. Adult males occupied coastal areas. Family groups and pregnant females occupied areas farther inland. Subadult females and males occupied similar habitats which overlapped with those of adult males. Avoidance of conspecifics, energy conservation, philopatry, denning habitat, and habitat selection appeared to influence observed patterns. A southward shift in the population was evident early in the ice-free period and was followed by a return movement northward during October and November. This may be due to ice-formation patterns which permit earlier access to the sea ice along the north coast and hunting habitat to the northeast. All bears moved less than bears on the sea ice, and movements were consistent with a strategy of energy conservation. Most bears appear to have travelled directly from the sea ice to the study area and remained until the sea ice reformed. Little exchange with adjacent populations and a high degree of philopatry were evident for all age and sex groups; this may be a function of the distribution of denning habitat, the winter distribution of sea ice habitat and seals, and the noncompetitive conditions that prevail during the ice-free period which make dispersal of limited benefit.