Estimating greater sage-grouse population sizes within Oregon, 2017–24

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We fit a binomial mixture (N-mixture) model to lek (breeding area) count data to estimate annual population sizes of greater sage-grouse (Centrocercus urophasianus; sage-grouse) within Oregon between 2017 and 2024.Population estimates were delineated among 24 priority areas for conservation, and additional sources of information were considered, including male-to-female sex ratios, lek attendance rates, numbers of unmodeled leks, and the existence of unsampled/unknown leks.In 2024, Oregon was estimated to contain approximately 41,875 sagegrouse (95-percent credible interval [CRI=38,980-54,634]), which was down from a high of 50,869 (95-percent CRI=41,794-66,238) in 2017.A nadir (low point) was identified during 2019, when the median statewide population estimate was 30,644 birds.A complete population oscillation was not evident during the inferential period based on local maxima that were observed during the start (2017) and stop (2024) years of analysis.In addition to estimating population sizes, we evaluated N-mixture model estimates for precision and accuracy after randomly removing single and repeat counts in 10-percent increments (relative to total sample size).We estimated an increase in absolute bias of approximately 1.6 percent for every 10-percent reduction in effort. Plain Language SummaryOregon's greater sage-grouse population was estimated using thousands of lek (breeding area) counts collected from 2017 to 2024, combined with statistical modeling that accounts for imperfect detection, sex ratios, birds that do not attend leks, and leks that are missing from the database.U.S. Geological Survey researchers fit a binomial mixture (N-mixture) model to lek count data to estimate annual population sizes and included all corrections.Model results revealed a statewide population decline from about 50,869 birds in 2017 to about 41,875 in 2024, with a low point of roughly 30,644 in 2019.The study also found that survey timing strongly affects detectability, counts were highest near sunrise, and that reducing survey effort increases bias in population estimates.Overall, the work provides Oregon's most comprehensive, data-driven sage-grouse population estimates to date and offers guidance for improving monitoring and conservation planning.

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