Saturday, September 8, 2012

Black vs. American Oystercatcher

Oswald West State Park is a small but remarkably beautiful Oregon State Park located south of Cannon Beach. Trails lead from a rest area on US Highway 101 to a sandy cove surrounded by forested hills. A freshwater stream flows from the forest into the sea. In the stream on the beach, we photographed a Black Oystercatcher. We later learned that Black Oystercatchers search for and bathe in freshwater streams.

You would not guess that telling a Black from an American oystercatcher presents much of a problem. Black Oystercatchers are found along the Pacific Coast, from the Aleutians to Baja California. The American is found along the East Coast, south through South America. The photo below is of a bird we saw earlier during our March road-trip along the Texas coast. Where their ranges overlap, in Baja California, the two species hybridize. Hybrids look like Black Oystercatchers with varying amounts of white. If the two populations hybridize, why aren't they considered one, variable species? Apparently the birds prefer to mate with similar looking birds. This preference breaks down only when population numbers are low and mates of the proper type can not be found (Andres and Falxa 1995).

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