Grizzly bear prehibernation and denning activities as determined by radiotracking

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Over a 9-year period, grizzly bears were studied by means of radiotracking. Eleven active dens were located. Den selection and digging may occur as early as 3 September. Dens were dug entirely by the grizzlies, and no natural shelters were utilized. Dens were not large, and all bed chambers were lined with bedding, usually boughs. The dens we located were not re-used, but circumstantial evidence suggested occasional re-use. It appears that den digging is instinctive behavior for the grizzly, and is reinforced by experience. Grizzlies traveled from fall foraging areas to sites over distances ranging from a few miles to 30 or more. Each year, grizzlies living under the same environmental conditions hibernated at about the same time. This concurrent entering of dens did not apply to bears at lower elevations and living under different conditions. The dates when grizzlies entered dens for their winter sleep were influenced by environmental factors and, during 9 years, varied by as much as a month. The bears usually entered their dens during snowstorms. This eliminated tracks and appears to have survival value for the species by protecting and isolating the grizzly bear during the period of its life when it is most vulnerable to man. In the fall of 1965, a prehibernation lethargy was observed in grizzly bears prior to entering their dens. The premature onset of lethargy appeared to have been activated by an unusually cold spell in September. When grizzlies emerge from winter sleep, winter-killed ungulates are major items in their diet.

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Reference Code: A72CRA01IDUS

Full Citation: Craighead, F. C., Jr., and J. J. Craighead. 1972. Grizzly bear prehibernation and denning activities as determined by radiotracking. Wildlife Monographs 32: 1-35.

Location: ANIMAL EF: URSUS ARCTOS