Interactions Of Sympatric Black And Grizzly Bears In Northwest Wyoming

Authors(s): G. W. Holm

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Publication Date: 0000-00-00

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Abstract: As the Greater Yellowstone Ecosystem grizzly bear population moves toward recovery goals in northwest Wyoming it will likely expand into areas occupied by black bears. Interactions between the species will influence the ease with which grizzly bears occupy new areas, and the effect grizzly bear expansion will have on resident black bear populations. I monitored movement and activity patterns of 13 radiocollared black bears and 17 radiocollared grizzly bears concurrently on a 450km^2 study area (Blackrock) in northwest Wyoming during 1995 and 1996. Hypotheses were tested to examine dispersion, activity patterns, habitat use, and diets of the 2 species. The larger home ranges of grizzly bears each overlapped by few grizzly bear core areas. Habitat use and activity patterns differed the least between black bears and adult female and sub-adult grizzly bears, and the most with adult male grizzly bears. Adult male grizzly bears used open habitats more than expected while black bears selected against these habitats. Adult male grizzly bears were nocturnal, sub-adult and adult female grizzly bears generally crepuscular, and black bears diurnal. Diets of the 2 species differed, perhaps indicating some adjustment to minimize the potential for contacts. Differences in distribution, habitat use, and activity patterns of black bears and adult male grizzly bears suggests sufficient ecological separation to reduce interactions. The similarities I observed in distribution, habitat use, and activity patterns of black bears and female and sub-adult grizzly bears however, suggest interactions between the species may increase as adult females become more established at Blackrock.

Keywords: Greater Yellowstone Ecosysttem, animal, mammal, bear, Ursidae, grizzly bear, black bear, Ursus arctos horribilis, Ursus americanus, population, Wyoming, radio collar, habitat, food, forage