Grizzly Bear: Habitat Relationships in the Yellowstone Area

Abstract

Habitat use by grizzly bears (Ursus arctos) was studied from 1977 through 1979 in a 20,000-km2 area with Yellow? stone National Park in the center. Of 1826 aerial radio locations of 46 instrumented grizzlies, 90% were in timber. Threefourths of the locations were 100 m or less from an edge between timber and an opening. Timber over 3 m tail with a canopy cover of 26-75% accounted for 50% of all activity sites from March through November. The Abies lasiocarpalVaccinium scoparium community alone contained 23% of the total activity sites and 35% of the forested activity sites. Of 507 observations of feeding activity, 45% were recorded in timber over 3 m tail with a canopy cover of 26-100%, 34% in timber with a 0.1-25% canopy cover, 20% in open habitats, and 3% in timber less than 3 m tail. Ninety-nine percent of examined day beds were in for? ested communities. Int. Conf. Bear Res. and Manage. 5:118-123 In 1975 the grizzly bear south of Canada was listed as a threatened species. To comply with the Endangered Species Act of 1973, Federal agencies must, therefore, avoid destruction or adverse modification of grizzly bear habitat. However, a lack of data has limited the ability of management agencies to define critical habitat and evaluate the effects of land use practices upon the grizzly. Research to determine the rela? tionships between grizzly bears and habitat has been continuing and data are accumulating. The use of timber as shelter by grizzlies has been documented (Jonkel and Cowan 1971; Craighead and Craighead 1972; J.Sumner and J.J. Craighead, unpubl. rep., Mont. Coop. Wild? life Res. Unit, Missoula, 1973; R. Knight et al., unpubl. annu. reps., Interagency Study Team, U.S. Dep. Inter., Park Ser., Bozeman, Mont., 1977, 1978; Roth and Osti 1979). Research has also determined that meadows are important for? aging habitats for grizzlies (Graham 1978, Mealy et al. 1977). The extent to which grizzly bears used timbered areas for foraging was unknown and has been an important management-related question; therefore, since 1977 the Interagency Grizzly Bear Study (IGBS) has addressed this problem. This paper reports the findings of the IGBS on grizzly bear-habitat relationships. Funding for this study was provided by the Na? tional Park Service and the U.S. Fish and Wildlife Service. The field work was facilitated by the cooperation of personnel from Yellowstone Nation? al Park, district U.S. Forest Service offices within the study area, and the wildlife departments of Wyoming, Idaho, and Montana. Special thanks are extended to the numerous IGBS seasonal em? ployees for gathering the data, to Dave and Roger Stradley for magnificent piloting throughout the years of the study, and to R. Knight and T. Weaver for critically reviewing the manuscript.