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Evaluation of rules to distinguish unique female grizzly bears with cubs in Yellowstone

Journal of Wildlife Management

By:
, , , and
DOI: 10.2193/2007-259

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Abstract

The United States Fish and Wildlife Service uses counts of unduplicated female grizzly bears (Ursus arctos) with cubs-of-the-year to establish limits of sustainable mortality in the Greater Yellowstone Ecosystem, USA. Sightings are dustered into observations of unique bears based on an empirically derived rule set. The method has never been tested or verified. To evaluate the rule set, we used data from radiocollared females obtained during 1975-2004 to simulate populations under varying densities, distributions, and sighting frequencies. We tested individual rules and rule-set performance, using custom software to apply the rule-set and duster sightings. Results indicated most rules were violated to some degree, and rule-based dustering consistently underestimated the minimum number of females and total population size derived from a nonparametric estimator (Chao2). We conclude that the current rule set returns conservative estimates, but with minor improvements, counts of unduplicated females-with-cubs can serve as a reasonable index of population size useful for establishing annual mortality limits. For the Yellowstone population, the index is more practical and cost-effective than capture-mark-recapture using either DNA hair snagging or aerial surveys with radiomarked bears. The method has useful application in other ecosystems, but we recommend rules used to distinguish unique females be adapted to local conditions and tested.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evaluation of rules to distinguish unique female grizzly bears with cubs in Yellowstone
Series title:
Journal of Wildlife Management
DOI:
10.2193/2007-259
Volume
72
Issue:
2
Year Published:
2008
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Wildlife Management
First page:
543
Last page:
554