Space-use strategies of female polar bears in a dynamic sea ice habitat

Abstract

In environments with high spatiotemporal variability in resources, animals may exhibit nomadic movements for resource tracking as opposed to long-term area fidelity. Polar bears (Ursus maritimus) inhabit the dynamic sea ice, preying on seals, and demonstrate considerable intraspecific variation in space use. We studied patterns of fidelity and annual range size for 74 adult female polar bears captured in the Norwegian Arctic that were tracked for up to 5 years using satellite telemetry data. We used the autocorrelation structure of movements and distance between observations at a 1-year interval as measures of fidelity. The female polar bears had a circannual migration pattern. Annual range size varied with reproductive state and geographic location of the range. Females entering maternity dens had smaller annual ranges than females not entering dens. Nearshore females had smaller annual ranges than pelagic females, demonstrating different space-use strategies. Repeatability of movement patterns indicated strategy specialization. We suggest that the different space-use strategies result from variation in habitat and prey selection and in sea-ice dynamics. Factors affecting population and predator–prey dynamics may interact differently with the different space-use strategies and yield strategy-dependent outcomes, therefore a knowledge of movement strategies may be important for understanding polar bear population dynamics.