A CASE OF OFFSPRING ADOPTION IN FREE-RANGING POLAR BEARS (URSUS-MARITIMUS)

During a study of the reproductive ecology of polar bears (Ursus marit imus) in western Hudson Bay (Canada), we documented a case of litter a doption. In an eight-month period, a ten-year-old adult female lost a litter of two cubs-of-the-year and adopted three other cubs-of-the-yea r. This is the first reported case of natural offspring adoption in po lar bears, and its significance as a reproductive strategy is unknown. Nevertheless, the observation raises questions regarding the social c ircumstances under which adoption may occur and the benefits or costs to maternal fitness in a solitary mammal such as the polar bear.