Grizzly Bear Population Vital Rates and Trend in the Northern Continental Divide Ecosystem, Montana

Authors

Richard D. Mace, Montana Fish, Wildlife and ParksFollow
Daniel W. Carney, Blackfeet Fish & Wildlife Department
Tonya Chilton-Radandt, Montana Fish, Wildlife and Parks
Stacy A. Courville, Confederated Salish and Kootenai Tribe
Mark A. Haroldson, U.S. Geological SurveyFollow
Richard B. Harris, University of MontanaFollow
James Jonkel, Montana Fish, Wildlife and Parks
Bruce Mclellan, British Columbia Ministry of Forests Research Branch
Michael Madel, Montana Fish, Wildlife and Parks
Timothy Manley, Montana Fish, Wildlife and Parks
Charles Schwartz, U.S. Geological SurveyFollow
Christopher Servheen, U.S. Fish and Wildlife Service
Gordon Stenhouse, Foothills Research Institute
John S. Waller, National Park ServiceFollow
Erik Wenum, Montana Fish, Wildlife and Parks

Date of this Version

2012

Citation

The Journal of Wildlife Management 76(1):119–128; 2012; DOI: 10.1002/jwmg.250

Abstract

We estimated grizzly bear (Ursus arctos) population vital rates and trend for the Northern Continental Divide Ecosystem (NCDE), Montana, between 2004 and 2009 by following radio-collared females and observing their fate and reproductive performance. Our estimates of dependent cub and yearling survival were 0.612 (95% CI = 0.300–0.818) and 0.682 (95% CI = 0.258–0.898). Our estimates of subadult and adult female survival were 0.852 (95% CI = 0.628–0.951) and 0.952 (95% CI = 0.892– 0.980). From visual observations, we estimated a mean litter size of 2.00 cubs/litter. Accounting for cub mortality prior to the first observations of litters in spring, our adjusted mean litter size was 2.27 cubs/litter. We estimated the probabilities of females transitioning from one reproductive state to another between years. Using the stable state probability of 0.322 (95% CI = 0.262–0.382) for females with cub litters, our adjusted fecundity estimate (m_x) was 0.367 (95% CI = 0.273–0.461). Using our derived rates, we estimated that the population grew at a mean annual rate of approximately 3% (λ = 1.0306, 95% CI = 0.928–1.102), and 71.5% of 10,000 Monte Carlo simulations produced estimates of λ > 1.0. Our results indicate an increasing population trend of grizzly bears in the NCDE. Coupled with concurrent studies of population size, we estimate that over 1,000 grizzly bears reside in and adjacent to this recovery area. We suggest that monitoring of population trend and other vital rates using radioed females be continued.