We documented the loss of brown bear (Ursus arctos) cubs-of-the-year (cubs) in 2 Swedish populations for 11 years in the north and 12 years in the south, and made spatial and temporal comparisons to examine whether nutritional, social (sexually selected infanticide), or den disturbance factors best explained the observed variation. Annual cub loss was 0.04 (n = 78) in the north and 0.35 (n = 126) in the south. The loss of cubs at both levels of comparison was best explained by social factors. Disturbance was only evaluated in the south and explained significant variation. In the north, few adult males died and 3 adult males lost early in the study there were not replaced for many years, presumably due to little immigration of new males. Immigration was probably low due to high illegal mortality around the study area and lack of bear habitat on one side of the study area. In the south, 5 times as many males died annually, and in years with recorded adult male mortality, an average of 20% of the adult males died. The number of adult males remained stable, presumably due to immigration by new males. Illegal mortality appeared to be less in the south, and the study area was surrounded by bear habitat. Number of adult males dying in cub areas (the composite area of all radiomarked females with cubs) 2 years previously was correlated negatively with cub survival in the south. In the north, no factors correlated with temporal patterns of cub loss, but loss of adult males 1-2 years previously was the best variable we tested. We suggest that immigrating males kill cubs, as predicted by the sexually selected infanticide hypothesis. Some other studies have yielded similar results. We recommend that managers assume that loss of adult male bears is depensatory until this question is adequately resolved.
- Volume 12
- Issue
- Pages 69-80
- Publication Date 1 January 2001
- DOI
- File Size 494.22 KB
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