Denning of Grizzly Bears in the Yellowstone National Park Area

Abstract

Radiotelemetry was used to locate 101 grizzly bear (Ursus arctos) dens from 1975 to 1980; 35 dens were examined on the ground. Pregnant females denned in late October, and most other bears denned by mid-November. Duration of denning averaged 113, 132, and 170 days for males, females, and females with new cubs, respectively. Males emerged from mid-February to late March, followed by single females and females with yearlings and 2-yearolds. Females with new cubs emerged from early to mid-April. Den sites were associated with moderate tree cover (26%-75% canopy cover) on 30?-60? slopes. Dens occurred on all aspects, although northerly exposures were most common. Grizzly bears usually dug new dens but occasionally used natural cavities or a den from a previous year. Males usually dug larger dens than females with young. Eight excavated and 2 natural dens of the 35 examined dens were used for more than 1 year. Int. Conf Bear Res. and Manage. 6:111-117 The Interagency Grizzly Bear Study Team has studied grizzly bears in and around Yellowstone Na? tional Park since 1973. One major objective was to identify grizzly bear habitat requirements. Grizzly bears occupy dens in the Yellowstone area for up to 6 months of each year and dens are therefore an important segment of the habitat. Intelligent man? agement decisions depend on knowing dates of den entry and emergence, general areas of denning, and site selection. We gathered data pertaining to these factors from fall 1975 through 1980. Craighead and Craighead (1972) did the original work on grizzly bear dens and denning habits in this area between 1963 and 1968. Since the completion of those studies, the Yellowstone grizzly bear pop? ulation has dispersed considerably because garbage dumps within the park have closed (Judd and Knight 1980). We acknowledge the assistance of many seasonal employees in investigating den sites, especially D. Burrup, L. Cayot, C. Hancock, C. Hunt, and H. Ihsle. M. Duffy piloted the helicopter when we marked den sites, and D. and R. Stradley piloted the planes used to gather data on den locations and denning and emergence dates. J. Beecham reviewed this manu? script.