On Saturday, May 22, 2010, I followed up on a report of an American Oystercatcher at a few locations in Laguna Beach. I tried Crescent Bay first, and was fortunate to find five Oystercatchers on the rocks below the point. Three were Black Oystercatchers, the other two looked pretty good for Americans. The problem is that Black and American Oystercatchers interbreed and their hybrid offspring can be anywhere on a cline from pure Black to pure American. Deciding what these birds were required some examination. A rating system developed by J. R. Jehl, Jr. is used by ornithologists to determine where on the cline a given bird falls. Because there are several genetic variations that are involved, ten different characteristics are judged, nine of them being rated 0 to 4, the belly coloration from 0 to 6. A score of 0 to 9 rates as a pure Black Oystercatcher, 30 to 38 as pure American, and everything in between as a hybrid.
The American Oystercatcher that is the main subject in this video has white upper tail coverts (Jehl’s score 4), basal half of all retrices were white (4), chest sharply delimited black to white on upper chest (4), belly entirely white (6), undertail coverts entirely white (4), thighs entirely white (4), greater secondary coverts 6-15mm (3), white present on some of inner primaries (3), underwing coverts entirely white (4), axillaries entirely white (4). Jehl’s score is 36 out of 38.
The hybrid Oystercatcher, seen on the left as the video starts, has upper tail coverts black (Jehl’s score 0), retrices mainly black with some white in the vanes (1), black chest bordered by jagged edge on upper chest (3), belly entirely white (6), undertail coverts mainly white (3), thighs entirely white (4), greater secondary coverts 6-15mm (3), white present on secondaries but not primaries (2), underwing coverts mainly white (3), axillaries entirely white (4). Jehl’s score is 28 out of 38, so close, but not close enough.