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Methods to estimate distribution and range extent of grizzly bears in the Greater Yellowstone Ecosystem

March 1, 2014

The distribution of the Greater Yellowstone Ecosystem grizzly bear (Ursus arctos) population has expanded into areas unoccupied since the early 20th century. Up-to-date information on the area and extent of this distribution is crucial for federal, state, and tribal wildlife and land managers to make informed decisions regarding grizzly bear management. The most recent estimate of grizzly bear distribution (2004) utilized fixed-kernel density estimators to describe distribution. This method was complex and computationally time consuming and excluded observations of unmarked bears. Our objective was to develop a technique to estimate grizzly bear distribution that would allow for the use of all verified grizzly bear location data, as well as provide the simplicity to be updated more frequently. We placed all verified grizzly bear locations from all sources from 1990 to 2004 and 1990 to 2010 onto a 3-km × 3-km grid and used zonal analysis and ordinary kriging to develop a predicted surface of grizzly bear distribution. We compared the area and extent of the 2004 kriging surface with the previous 2004 effort and evaluated changes in grizzly bear distribution from 2004 to 2010. The 2004 kriging surface was 2.4% smaller than the previous fixed-kernel estimate, but more closely represented the data. Grizzly bear distribution increased 38.3% from 2004 to 2010, with most expansion in the northern and southern regions of the range. This technique can be used to provide a current estimate of grizzly bear distribution for management and conservation applications.

Publication Year 2014
Title Methods to estimate distribution and range extent of grizzly bears in the Greater Yellowstone Ecosystem
DOI 10.1002/wsb.368
Authors Mark A. Haroldson, Charles C. Schwartz, Daniel J. Thompson, Daniel D. Bjornlie, Kerry A. Gunther, Steven L. Cain, Daniel B. Tyers, Kevin L. Frey, Bryan C. Aber
Publication Type Article
Publication Subtype Journal Article
Series Title Wildlife Society Bulletin
Index ID 70131504
Record Source USGS Publications Warehouse
USGS Organization Northern Rocky Mountain Science Center