Thayer's Gull, Larus thayeri
Thayer's Gull, adult winter, 2/25/05, Jetty Road, Moss Landing, Monterey Co
Thayer's Gull, first winter, 2/3/09, Princeton Harbor, San Mateo Co
Thayer's Gull, first winter, head profile, 2/3/09, Princeton Harbor, San MateoCo
A first-winter Thayer's Gull, above with full profile, and left, a more direct profile view of the head.
Thayer's Gull, third winter, 11/20/04, Gualala River mouth, Sonoma Co
This is a third winter bird, mostly adult plumage. There's some dark spotting on the tail, a little brown in the wings, and the gonydeal mark is black instead of red, as in the adult winter bird above. The bill shape is right for Thayer's, as is the dark eye, mantle color (between Herring and California), and the dark pink leg color. The rounded head is also right for Thayer's. As Mike Mammoser pointed out to me, the clincher is the barely visible underside of the primaries, which are much paler than the upperside, in the distinctive Thayer's pattern.