Estimating greater sage-grouse population sizes within the state of Oregon, USA 2017-2024

Abstract

We fit an N-mixture model to lek (breeding area) count data to estimate annual population sizes of greater sage-grouse (Centrocercus urophasianus; sage-grouse) within the state of Oregon, USA between 2017-2024. Population estimates were delineated among 24 Priority Areas for Conservation (PACs) and considered additional sources of information including male-to-female sex ratios, lek attendance rates, numbers of unmodeled leks, and the existence of unsampled/unknown leks. In 2024, the state of Oregon was estimated to contain approximately 41,875 sage-grouse (95% credible interval [CRI] = 38,980-54,634), which was down from a high of 50,869 (95% 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% increments (relative to total sample size). We estimated an increase in absolute bias of approximately 1.6% for every 10% reduction in effort.