Encounter Competition between Bears and Cougars: Some Ecological Implications

Black bears (Ursus americanus) or grizzly bears (Ursus arctos) visited 8 of 55 cougar-killed (Felis concolor) ungulates in Glacier National Park (GNP), Montana, from 1992 to 1995, and 19 of 58 cougar kills in Yellowstone National Park (YNP), Wyoming, from 1990 to 1995. Bears displaced cougars from 4 of 8 carcasses they visited in GNP and 7 of 19 in YNP. Cougar predation provided an average of 1.9 kg/day (range = 0-6.8 kg/day) of biomass to bears that fed on cougar-killed ungulates. This biomass was an important percent (up to 113%) of the daily energy needs of bears when compared to their caloric requirements reported in the literature. We suggest that ungulate carrion resulting from cougar predation is important nutritionally to bears in some regions and seasons. Cougars that were displaced from their kills by bears lost an average of 0.64 kg/day of ungulate biomass, or 17-26% of their daily energy requirements. Biologists modelling or measuring cougar predation rates should be aware that losses to scavengers may be significant.