Black Oystercatcher nesting season has begun in California, and a network of Audubon and agency observers are tracking the success of breeding birds from Mendocino to Morro Bay. All told, over 80 people in nine counties visit one or more nest sites at least once a week to check the status of oystercatcher nests. The information gathered by these dedicated observers is providing vital insight into the status of these charismatic, beloved rocky intertidal shorebirds in California. (All photos by Ron LeValley)
The Black Oystercatcher is unique in both appearance and life history. Of the six rocky intertidal obligate shorebirds, it is the only species residing here year-round. Oystercatchers range from Baja to the Aleutian Islands, making their living among wave-swept mussel beds by sneaking up behind limpets and prying them off the rocks, and hunting for snails, mussels and other invertebrates. In our state, they mainly nest on islets and offshore rocks of the California Coastal National Monument (CCNM). Oystercatchers prefer nesting sites on rocks that are separated from the mainland, laying one to three eggs from May to June depending on latitude. They aggressively defend their territories from intruders including other oystercatchers.
Black Oystercatchers are a US Fish and Wildlife Service Focal Species due to their small global population size of under 20,000 individuals as well as vulnerability to threats such as sea level rise, increased storm events, oil spills and disturbance. Until recently, very little was known of its population size and distribution in California. In 2011, Audubon California coordinated the first targeted statewide survey for the species, showing far higher abundances than had been thought, as well as areas of very high densities.
Now, biologists and citizen scientists such as Jodi Isaacs of California State Parks, Diane Hichwa of Madrone Audubon, Joleen Ossello of Mendocino Coast Audubon, Hugo Ceja for the California Coastal National Monument, and Meg Marriott of the U.S. Fish and Wildlife Service are coordinating volunteers and themselves tracking nest success toward the goal of a five-year data set that will shed light on the trajectory of the species in California. Mendocino Coast Audubon has gone further by producing outreach materials on oystercatchers reaching thousands of coastal residents and visitors, and educating coastal users to reduce disturbance to nests during the breeding season.
At the same time, Audubon California is supporting these individuals through contracts and/or through overall coordination of the statewide effort. We are also establishing a monitoring program for oystercatchers at a subset of California’s new network of marine reserves, where they serve as an indicator species for the health of the state’s iconic rocky intertidal habitats. Finally, we are working with the CCNM to identify and map anticipated changes to oystercatcher habitat in California as the ocean climate changes. Collectively, the Audubon network is helping understand , conserve and enjoy this wonderful and uncommon shorebird.