Technical Report

 

Analysis of Greater Sage-grouse Lek Data: Trends in Peak Male Counts 1965-2015 Public Deposited

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  • Trends in greater sage-grouse breeding populations are typically indexed by determining the peak number of males attending a lek in a lekking season. Numerous studies have estimated negative trends in sage-grouse breeding populations over time via data collected for the last 50 years. However, the inherent bias in data collection and unknown relationship between lek counts and population size limits the utility of using counts to evaluate range-wide population trends. This study estimated trends in the male segment of greater sage-grouse breeding populations within core and periphery areas in seven habitat management zones during two time periods, 1965-2015 and 2005-2015. In addition, we compared analysis methods used in this study to previous studies, and provided recommendations on future data collection. We developed a hierarchical model that followed individual leks through time and allowed trends at individual leks to inform estimates of regional trends. We fit overdispersed Poisson models using a Bayesian hierarchical framework and Markov-chain Monte Carlo (MCMC) methods. The average range-wide decline, weighted across management zones, was 2.10% per year, for an average total decline of 66% from 1965-2015. Estimates of trend over 2005-2015 for individual management zones, in both core and periphery areas, indicated that recent annual declines were more severe compared to the average declines over the entire analysis period 1965-2015. The declines estimated in this study were similar to other studies; however, review of the literature reveals numerous issues surrounding the historical data, the on-going monitoring and sampling scheme, and utilization of various statistical methods, all of which limit our inference on population trends. We believe the overdispersed Poisson regression model is the most appropriate analysis method for these and future data, regardless of whether the focus remains on peak male counts or total counts of observed sage-grouse based on a more spatially balanced sample of monitoring sites that are randomly selected.
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  • Nielson, R. M., L. L. McDonald, J. Mitchell, S. Howlin, and C. LeBeau. 2015. Analysis of greater sage-grouse lek data: Trends in peak male counts 1965-2015. Western EcoSystems Technology, Inc., Cheyenne, Wyoming, USA.
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  • 43 pages
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  • Prepared for: Western Association of Fish and Wildlife Agencies 522 Notre Dame Court, Cheyenne, WY 82009
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