[Mystery birds] Harlequin Ducks, Histrionicus histrionicus (mostly males, but there is a female in the foreground), photographed at low tide at Haystack Rock, Cannon Beach, Oregon. [I will identify these birds for you in 48 hours]
Image: Terry Sohl, 8 June 2009 [larger view]
Photo taken with a Canon 50D, 400 5.6L.
Are all the birds in this image the same species?
Please name at least one field mark that supports your identification.