The Black Oystercatcher is a large shorebird found along the west coast of North America. Because of its small global population size, low reproductive rate, and dependence on rocky intertidal habitats, it is considered a “species of high conservation concern” and may act as an indicator of intertidal ecosystem health. In 2015, Portland Audubon initiated a 3-y shore-based population survey in Oregon building upon long-term monitoring previously conducted by the US Geological Survey (USGS) and others. The objectives were to: (1) estimate the current minimum population of breeding Black Oystercatchers in Oregon and compare to previous estimates; (2) document oystercatcher abundance on shoreline adjacent to the Oregon's system of Marine Reserves (MRs) and Marine Protected Areas (MPAs); and (3) describe the spatial distribution of breeding oystercatchers along the coast. We targeted all rocky shoreline along Oregon's coastline to conduct abundance surveys each spring from 2015–2017. A total of 75 survey routes were sampled using a standardized land-based survey protocol. Trained volunteer community scientists conducted the majority of the surveys. We used N-mixture statistical models to estimate oystercatcher population size and probability of detection. Population estimates from the best-fitting models were consistent, with estimates ranging from 506 oystercatchers in 2016 (95% credible interval, 463–560) to 629 (548–743) in 2015. These estimates described a small but stable population. Probability of detection remained consistent across years (ranging from 0.51 to 0.53). Breeding density of oystercatchers was higher in southern Oregon. Oystercatcher abundance adjacent to MRs-MPAs accounted for between 12.4–18.3% of the total population estimate, which was lower than expected (approximately 25%). Subsequent conservation efforts for Black Oystercatchers in Oregon could be successful by focusing on limiting human disturbance, particularly on the north and central coasts, and protecting core habitats on the south coast where much of the population resides.
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Vol. 101 • No. 1