Searching, Always Searching
In western Hudson Bay, Canada, near the southern extent of their range, polar bears (Ursus maritimus) may fast for periods of 4 months or longer. Except for pregnant females they do not den, but rather they engage in what is termed “walking hibernation” and are always foraging. These fasting polar bears that remain active have much higher energy demands, with metabolic rates similar to the basal metabolic rates of mammals in general. The degree to which polar bears can derive sufficient energy during prolonged periods of fasting affects individual survival. They can lose up to one-half their body mass. Photo © copyright by Robert Faucher.