Black Oystercatcher <i>Haematopus bachmani</i> Productivity in California and Oregon and the Effects of Nest Site and Environmental Covariates

Black Oystercatcher Haematopus bachmani is a species of conservation concern due to its small global population, reliance on somewhat restricted intertidal habitat, and vulnerability to climate change impacts. Concern for this species, along with a lack of demographic information from the southern portion of its range, gave rise to a community science project to monitor pair productivity, nest characteristics, and nest disturbance from 2012 through 2022 across three study regions in Oregon and California. A clear spatial gradient existed in productivity, with relatively low values in the southern region (0.37 fledged young per pair per year, 95% confidence interval [CI] = 0.32– 0.43; Southern California) compared to central (0.46, 0.41–0.51; Northern California and southern Oregon) and northern (0.60, 0.47–0.77; northern Oregon) regions. While productivity varied systematically across space, there was no general trend over time. Pair productivity was slightly higher at mainland nests than island nests when nest position above high tide was low, but it was highest at island nests when nest position was high. Productivity was negatively related to observed human disturbance but not consistently related to non-human disturbance or food availability, represented by estimates of mussel bed cover and depth near nests. We discuss our results in light of known and anticipated impacts of ocean and climate change on intertidal habitats of the coastal northeast Pacific region. We provide management recommendations and suggest avenues of new research to help in the conservation of this vulnerable species.