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Yellowstone grizzly bear investigations: Annual report of the Interagency Grizzly Bear Study Team, 2001

January 1, 2002

The contents of this Annual Report summarize results of monitoring and research from the 2001 field season. The report also contains a summary of nuisance grizzly bear (Ursus arctos horribilis) management actions.

In addition to our normal monitoring, we completed an array of studies addressing the potential impacts of winter recreation on denning grizzly bears. This research was in response to a lawsuit filed against the Gallatin National Forest and subsequent need to develop a biological assessment addressing effects of snowmobile use on grizzly bears (Chemy 2001). Research results were also used by the National Park Service for a biological assessment and winter use plan (U.S. Department of the Interior 2001). The Interagency Grizzly Bear Study Team (IGBST) was able to use existing data collected from collared bears to address several issues and data needs for both agencies. Denning chronology (Haroldson et al. 2002), denning areas (Podruzny et al. 2002), and grizzly distribution (Schwartz et al. 2002) were all addressed. Information from these studies was presented at the International Association for Bear Research and Management (IBA) in Jackson Hole, Wyoming in 2001, and all 3 manuscripts have been officially accepted for publication in the journal Ursus. Abstracts are attached to this report (Appendices A, B. and C). Additionally, members of the study team participated in a workshop held by the National Park Service to develop monitoring protocols addressing the impacts of snowmobiles on wildlife (Graves and Reams 2001).

The study team has also been working on issues associated with counts of unduplicated females with cubs-of-the-year (COY). These counts are used to establisha minimum population size, which is then used to establish mortality thresholds for the Recovery Plan (U.S. Fish and Wildlife Service [USFWS) 1993). Efforts by the Study Team to calculate more statistically sound estimates of population size have been underway for sometime. Eberhardt and Knight (1996) applied a Peterson-type capturemark-recapture estimator to unduplicated counts, and Boyce et al. (1999) recommended a maximum likelihood method. These methods assumed equal sightability of families, which was unrealistic for the Yellowstone population. Consequently, Boyce et al. (2001) recommended using a negative binomial distribution but found that they obtained reasonable results only when the coefficient of variation among sightings was assumed to be constant overtime. This assumption is also difficult to justify.

Recent work by the study team (Keating et al. 2002) evaluated the application of 7 nonparametric estimators to assess their performance in determining the number of females with COY in a given year. This work identified 2 estimators that performed well using Monte Carlo simulations over a range of sampling conditions deemed plausible for the Yellowstone population: Chao's estimator (Chao 1984) and the sample coverage estimator (Chao and Lee 1992, Lee and Chao 1994). This work was presented at the IBA meeting in Jackson and the manuscript has been accepted in the journal Ursus. An abstract of this work is attached to this annual report (Appendix D). We are currently refining the application of these techniques to expand the predicted number of females with COY into a total population estimate. We anticipate completion of that work in 2002 or 2003.


Publication Year 2002
Title Yellowstone grizzly bear investigations: Annual report of the Interagency Grizzly Bear Study Team, 2001
Publication Type Report
Publication Subtype Federal Government Series
Series Title Annual Report
Index ID 70159733
Record Source USGS Publications Warehouse
USGS Organization Northern Rocky Mountain Science Center