Results of Landmark Montana Grizzly Bear Study Now Available

It took a team of more than 200 researchers and crew members to sample the grizzly bear population in a 7.8 million-acre area in northwest Montana stretching from north of Missoula, Mont., to the Canadian border. The 5-year study is the largest noninvasive study of bears to date. And now the team, consisting of 12 federal, state, and tribal agencies, landowners, universities, and other entities, can see the fruits of their labor featured on the cover of the January 2009 issue of the Journal of Wildlife Management.

USGS Biologist Kate Kendall, the principal author, led a team of researchers to complete this landmark project: the first ever ecosystem–wide scientific assessment of grizzlies in the Northern Continental Divide Ecosystem (NCDE).

The Northern Divide Grizzly Bear Project estimated 765 grizzly bears make their home in the NCDE. Initiated in 2003, the study provides a better understanding of the population size, distribution, and genetic health of grizzly bears in northwest Montana.

The recently published article, Demography and Genetic Structure of a Recovering Grizzly Bear Population, describes the noninvasive methods used to collect hair from bears without the need to handle them. Hair was collected from bear rubs (bears naturally rub against trees and posts) and systematically distributed hair traps that made use of scent lure to attract bears. Approximately 13,000 samples were collected from bear rubs and 21,000 were collected from hair traps, providing researchers with a total of 34,000 bear hair samples.

Through the use of genetic analysis of the hair samples, researchers were able to determine the total number of bears sampled and track their detections in time and space. Genetic analysis identified 563 individual grizzly bears. Using statistical models to calculate the number of bears not sampled and incorporate them into an estimate of population size, the total grizzly bear population in this region was estimated to be 765.

Researchers were also able to examine the proportion of females, genetic health, and amount of occupied habitat of the grizzly bear population. Kendall and her colleagues estimate that 470 of the 765 bears were females and found that females were present in throughout the study area. The number and wide distribution of females indicates good reproductive potential. The study also found that the occupied range of the grizzly bears now extends 2.6 million acres beyond the recovery zone boundary set by the U.S. Fish and Wildlife Service in the Grizzly Bear Recovery Plan. Overall, the genetic health of this population is good, resembling levels seen in relatively undisturbed populations in Alaska and Canada. However, early signs were detected that human development has begun to inhibit interbreeding between bears across one part of the main transportation corridor in the ecosystem.

This study highlights the need for a more intensive program than is currently described in the recovery Plan to monitor population status and to determine if mortality rates are sustainable. Baseline data collected from the Northern Divide Grizzly Bear Project are aimed at helping federal, state, and tribal wildlife agencies in managing the northwest Montana grizzly population. It will also assist the Montana Department of Fish, Wildlife, and Parks in conducting grizzly population trend studies and help the U.S. Fish and Wildlife Service with monitoring program efforts and recovery criteria.

For more information, visit the Northern Divide Grizzly Bear Project website or contact USGS Research Biologist Kate Kendall.