Polar bear foraging in western Hudson Bay.

28 pages : illustrations (chiefly color), map ; 26 cm.During much of the year, polar bears in western Hudson Bay use energy-conserving hunting tactics, such as still-hunting and stalking, to capture seals from sea-ice platforms. Such hunting allows these bears to accumulate a majority of the annual fat reserves that sustain them on land through the ice-free season. As climate change has led to earlier spring sea-ice breakup in western Hudson Bay, polar bears have less time to hunt seals, especially seal pups in their spring birthing lairs. Concerns have been raised as to whether this will lead to a shortfall in the bears' annual energy budget. Research based on scat analyses indicates that over the past 40 years at least some of these polar bears eat a variety of food during the ice-free season and are opportunistically taking advantage of a changing and increasing terrestrial prey base. Whether this food will offset anticipated shortfalls and whether land-based foraging will spread throughout the population is not yet known, and full resolution of the issues requires detailed physiological and genetic research. For insight on these issues, we present detailed observations on polar bears hunting without an ice platform. We compare the hunting tactics to those of polar bears using an ice platform and to those of the closely related grizzly bear. We examine how the techniques are related and explore how they may have evolved. We also discuss how they may contribute to polar bear adaptability in the face of climate change projections