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Jan 15 / USGS Newsroom

Results of Landmark Montana Grizzly Bear Study Now Available

With an estimated population of 765, the genetic health of grizzly bears in northwest Montana is good, according to a study recently released in the publication Journal of Wildlife Management. 

The Northern Divide Grizzly Bear Project sampled the grizzly bear population in the Northern Continental Divide Ecosystem (NCDE), a 7.8 million-acre area in northwest Montana stretching from north of Missoula, Mont., to the Canadian border.  Initiated in 2003, the project was the first ever ecosystem-wide scientific assessment of grizzlies in the NCDE and the largest non-invasive study of grizzly bears to date, providing a better understanding of the population size, distribution, and genetic health of grizzly bears in northwest Montana. 

A team of more than 200 researchers and crew members, led by U.S. Geological Survey (USGS) Biologist and principal author Kate Kendall in cooperation with 12 federal, state, and tribal agencies, landowners, universities, and other entities sampled the NCDE grizzly bear population over a span of 5 years. Results from the study are currently featured in the January 2009 cover article of the Journal of Wildlife Management in print and online. 

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The recently published article, Demography and Genetic Structure of a Recovering Grizzly Bear Population, describes the non-invasive methods used to collect hair from bears without handling the animals.  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 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 the region was estimated to be 765. 

Proportion of females, genetic health, and amount of occupied habitat of the grizzly bear population were also examined.  Kendall and her colleagues estimate that 470 of the 765 bears are females and found that females are distributed throughout the study area, indicating 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, it was also detected that human development has begun to inhibit interbreeding between bears across one part of the main transportation corridor in the ecosystem.   

The study highlights the need for a more intensive program than is currently described in the recovery plan to monitor population status and 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.  They 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. 

To view the recently published article, please visit the Wildlife Society Web site.

More information about the Northern Divide Grizzly Bear Project can be found on the Internet. 

For a podcast interview with USGS Scientist Kate Kendall about the project, listen to episode 64 of CoreCast at

[Via USGS]

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