Interactions of Sympatric Black and Grizzly Bears in Northwest Wyoming

As the grizzly bear (Ursus arctos) population in the Greater Yellowstone Ecosystem (GYE) moves toward recovery, it will expand into more areas occupied by black bears (U. americanus). Interactions between the species may affect resident black bear populations and also influence the ease with which grizzly bears recolonize. We monitored movement and activity patterns of 17 radiocollared grizzly bears and 13 radiocollared black bears on a 450 km2 area in northwest Wyoming during June-October in 1995 and 1996 and tested hypotheses predicting similarity in dispersion, activity, and habitat use patterns of sympatric black and grizzly bears. The larger home ranges of grizzly bears overlapped a number of black bear home ranges, yet core use areas were less likely to overlap. Adult male grizzly bears used open habitats more than expected (P ≤ 0.05), whereas black bears selected against them and used forested habitats more than expected (P ≤ 0.05). Patterns of black bear habitat use were more similar to those of adult female and sub-adult grizzly bears than adult male grizzly bears. Male grizzly bears were nocturnal, female grizzly bears were generally crepuscular, and black bears were diurnal. Differences in distribution, habitat use, and activity patterns suggested sufficient separation to reduce interactions between black bears and adult male grizzly bears. However, similarities between black bear and female and sub-adult grizzly bear patterns suggest that interactions between the species will become more common as adult female grizzly bears become established.