Cannibalism by black bears in the Nimpkish Valley, British Columbia

We studied black bears (Ursus americanus) between 1992 and 1995 in the Nimpkish Valley, Vancouver Island, British Columbia. During 1994, we observed 4 incidents of cannibalism by black bears. One incident of cannibalism occurred on a denned, radio-collared female that was consumed 390 m from her den and her two-cub litter that was consumed at the den site. The second incident involved a radio-collared male who consumed a female and her cub near their possible den site soon after den emergence. The third incident was one cub of a two-cub litter that was consumed 39 days after its radio-collared mother emerged from her den. The fourth incident was a subadult female attacked by an adult male during autumn before hibernation. Several authors have hypothesized that males kill unrelated cubs to increase their reproductive fitness. In our study, cannibalistic behavior of male bears is unlikely to have enhanced reproductive fitness because the bears involved were residents within their mating ranges, thus there is a high likelihood that the cubs were related to the aggressor. The high incidence of cannibalism in our study during 1994 is puzzling and inconsistent with explanations which attribute this behavior to enhancement of the fitness of male bears.