Intraspecific Predation in Scandinavian Brown Bears Older than Cubs-of-the-Year

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Intraspecific predation of bears >1 year old is observed occasionally, but the mechanisms behind it are poorly understood and often debated. We documented 13 cases of intraspecific predation in brown bears (Ursus arctos) in 2 Scandinavian study areas during 668 bear-years of radiotracking 238 brown bears. We found area differences in the rates of intraspecific predation only for yearling females. Annual yearling female mortality due to intraspecific predation was higher (0.162, 6 of 38) in the south than in the north (no mortality recorded, 28 yearlings followed). No older subadult females were killed by other bears. Annual mortality rates due to intraspecific predation for males, areas combined, were: 0.032 for yearlings, 0.040 for 2-year-olds, and 0.061 for 3-year-olds, for a combined rate from age 1 through 3 years of 0.127. One adult female was killed. Staying with their mother did not significantly reduce intraspecific predation among yearlings. Neither population density, at the levels we observed, nor reduced food abundance influenced rates of intraspecific predation on yearlings in our areas. In our study areas, intraspecific predation on yearling females was correlated positively with the number of adult males that had died 3 years previously and whether any adult male had died 2 years previously. In an earlier study, we found that cub mortality was elevated during the breeding season 2 years after the death of adult males. As we found a similar pattern for intraspecific predation on yearling females, we speculate that infanticidal males may be prone to kill subadult bears. Although based on a relatively small sample of mortalities, our results strengthen our earlier conclusion that the killing of adult males may have a population consequence that managers should consider.