นกนางนวลหลังเทา Larus schistisagus

Thickset, short-winged, pot-bellied gull. Adult has dark gray back and wings, intense pink legs, and an especially large white “crescent” (white tertial edges) near the wingtips when perched. Breeding adult white-headed; nonbreeding birds have variably heavy brown streaking on the head and upper breast. Takes four years for immatures to progress from mostly brown to fully white and gray adult plumage; intermediate plumages are often mottled and messy. Often looks rather frosty by the first winter; starts to develop a gray back and whitish eye in its second year. Primarily an Asian species, found in coastal regions from Japan and South Korea to Russia. Regularly occurs in western Alaska, but very rare elsewhere in North America.