TESTS OF HYPOTHESES FOR SEXUAL SEGREGATION IN GRIZZLY BEARS

We studied 2 grizzly bear (Ursus arctos) populations to test 3 hypotheses of sexual segregation. The ''no avoidance'' hypothesis predicts that females do not avoid males and male-occupied habitats but simply have different habitats available to them within their home ranges. The ''food'' hypothesis predicts that subadult and adult females avoid males because of competition or cannibalism by males for food. The ''sex'' hypothesis predicts that only sexually mature adult females avoid males because of sexually motivated infanticide by nonsire males. Sexually mature females avoided (P < 0.05) food-rich, male-occupied habitats in Kananaskis, Alberta, but selected (P < 0.05) such habitats in the Selkirk Mountains of Idaho. Sexually immature females selected (P < 0.05) food-rich, male-occupied habitats in both areas. Unequal availability of habitat did not explain the pattern of segregation because food-rich habitats were available to all age-sex classes. Competition or cannibalism by males did not explain segregation because only sexually mature females avoided male-occupied habitats in Kananaskis and no females avoided males in the Selkirks. Adult female avoidance of potentially infanticidal, nonsire, immigrant males in Kananaskis appeared to explain the pattern of segregation. High mortality of older males in Kananaskis coincided with an influx of younger, potentially infanticidal, immigrant males, and adult females avoided those males and their favored habitats. No such segregation was observed in the Selkirks where mortality of older males was low and where there were few or no immigrant males. Results are inconsistent with the no avoidance and food hypotheses but consistent with the sex hypothesis of sexual segregation.