Bird Lore: Black Oystercatcher

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The Black Oystercatcher is a mostly permanent resident where the Pacific Ocean breaks against rocky shorelines. It is uncommon in the Inland Marine Waters of Washington, but can be seen flying by the Edmonds waterfront from time to time. It is best to keep an eye out for this black shorebird with its longish dark orange bill in spring and fall. That is when it tends to wander a bit from its breeding territory.

The Black Oystercatcher favors rocky shorelines with small offshore islands where predators are few. In winter it can also be found on mudflats. Its diet is mostly mussels, limpets, and other shellfish such as whelks, urchins, crabs, and marine worms. It forages mostly near low tide and tends to loaf and rest at higher tides. When feeding on mussel beds it typically removes the mussel from its shell, leaving the shell in place.

It is thought that the Black Oystercatcher mates for life. It almost always nests on islands, A pair will defend its breeding territory that includes an elevated area for nesting above the high tide line and a feeding area with mussel beds or another food source. Box sexes build the nest, which is nothing more than a slight scrape lined with pebbles and pieces of shell. It is on gravel, a grassy area, or a depression in rock, well above the high tide mark.

Both adults incubate the two to three eggs for a period of 24-29 days. After hatching, the downy young remain near the nest while the parents take turns guarding them and bringing food. When the chicks are older they follow their parents to feeding areas where the adults still feed them. The chicks slowly begin to catch some of their own food. Young birds may eat fewer mussels at first because they lack the skill to open the shells.

The oldest Black Oystercatcher of record was six years and two months of age when recaptured in a British Columbia banding operation. A different source says that this species can live for more than 15 years. If you see a group of more than two, it’s a parcel of oystercatchers.

The Black Oystercatcher is widespread from Alaska to Baja California, but it is at risk at risk of becoming threatened or endangered without conservation action. It made the 2014 State of the Birds watch list because of its vulnerability to oil spills and other intertidal zone pollution. It is also sensitive to disturbance at its nesting sites by humans or introduced species (cats, foxes, rats). An example of the impact of human disturbance was seen on Destruction Island, off the Washington coast. In the seven years following automation of the lighthouse, the number of breeding pairs increased from four to twelve. The Aleutian Islands offer an example of how this species rebounds when mammalian disturbance is eliminated. The eradication of arctic red foxes has led to the return of the Black Oystercatcher.

You can hear Black Oystercatcher vocalizations, from two birds perched on a rock near Anacortes, here: https://www.xeno-canto.org/351803.

By Carol Riddell

Carol Riddell manages the bird education displays, on behalf of Pilchuck Audubon Society and Edmonds Parks & Recreation, at the Olympic Beach Visitor Station.

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