© A. R. Dean

Yellow-legged Gulls with otherwise adult-like plumage (including all-white tail) and adult-like bare parts but with black markings on primary coverts can be assumed to be in their fourth-winter, though this appearance is typical of third-winter individuals. See similar plumage of a known third-winter individual in early November 2011, though that individual also has less advanced bare parts and a smaller mirror on the outermost primary. Note absence of mirror on p9. Most 4W are little different from adults and will have mirrors on outer two primaries, though some may retain fine dark marks on pc..