Changes in mortality of Yellowstone's grizzly bears




Records of grizzly bear (Ursus arctos) deaths are currently used by managers to indicate trends in actual grizzly bear mortality and to judge the effectiveness of management. Two assumptions underlie these current uses: first, that recorded mortality is an unbiased indicator of actual mortality, and second, that changes in mortality after implementation of management strategies are sufficient grounds to infer the effects of management. I examined the defensibility of these 2 assumptions relative to alternate explanations, circumstantial evidence, and the potential costs of error. The potentially complex relation between actual and recorded mortality, as currently tallied and used, was reason to expect that the association between these 2 values would be weak. This expectation was supported by the prevalence (60-76%) of radio-marked bears among recorded deaths, the variation in apparent likelihood of documentation among causes of death, and variation in the prevalence of different causes over time. For these reasons, recorded mortality is likely to be an unreliable indicator of actual mortality. Use of whitebark pine (Pinus albicaulis) seeds by grizzly bears had a major effect on annual variation in recorded mortality. Low numbers of recorded deaths, 1984-92, were attributable to relatively frequent large whitebark pine seed crops. There was little or no residual trend potentially ascribed to management intervention during 1976-92. Management intervention was probably responsible for observed changes in recorded causes of death and stabilized recorded mortality over the period covered by this analysis.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Changes in mortality of Yellowstone's grizzly bears
Series title Ursus
Volume 10
Year Published 1998
Language English
Publisher International Association for Bear Research and Management
Contributing office(s) Forest and Rangeland Ecosystem Science Center
Description 10 p.
First page 129
Last page 138
Public Comments Part of a Special Issue: A Selection of Papers from the Tenth International Conference on Bear Research and Management, Fairbanks, Alaska, July 1995, and Mora, Sweden, September 1995
Country United States
State Idaho, Montana, Wyoming
Other Geospatial Yellowstone National Park
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