Black Oystercatcher Population Surprises Scientists

In June, Audubon California and the U.S. Fish and Wildlife Service led expert birders and biologists in a study of the Black Oystercatcher. Scientists were surprised at the number of sightings of the threatened bird they received. A total of 1,346 birds and 175 nests were counted. When compared against the total amount of suitable habitat, this preliminary result suggests the total number of breeding oystercatchers in the state may be higher than the last estimate of approximately 1,000-1,200 individuals. The bird’s population size is ultimately regulated by the availability of high quality nesting and foraging habitats.

(photo of Black Oystercatcher from USFWS)

The shorebird is one of the most distinctive birds in all of North America. The global population of the species is only 10,000. It is entirely black, with bright yellow eyes and a bright red bill. Biologists consider the size of the Black Oystercatcher’s population a good indicator of the overall health of the rocky intertidal community in California.

The successful population survey took place in 13 counties along the entire California Coastline where the Black Oystercatcher, Haematopus bachmani, lives year round. The goal of the project was to answer some fundamental questions about the species and its distribution in California.

“This is good news, especially considering the Black Oystercatcher’s vulnerability to human disturbances,” said Anna Weinstein, seabird program director. “It is completely dependent upon marine shorelines throughout its life cycle, which means we cannot forgo continued conservation efforts.”

The highest bird densities were reported from Mendocino and Sonoma counties. The highest nest densities reported were 12 nests/10 linear km. A few pairs of nests were within 30 meters of each other. Virtually all nests were located on rocks tidally separated from shore and with high shelves and niches for nests.

“With this information, conservation efforts can be directed to address specific issues like survival and reproduction success,” said Weinstein. “The next step is to determine what these action items are.”

Audubon chapters involved included: Mendocino, Redwood Region, Madrone, Golden Gate, and Morro Bay. The Bureau of Land Management’s California Coastal National Monument is a key agency partner. Other agencies involved included the U.S. Fish & Wildlife Service, California State Parks, National Park Service, and the U.S. Geological Survey. Other organizations included the Audubon Canyon Ranch, Mad River Biologists and Carter Biological Consulting.

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