Uncommon breeder in W. Rare but regular migrant to E, mostly winter. Easily overlooked. ID: 4-yr gull. Intermediate between RBGU and HEGU in size (including bill) and features. Found with both so comparison usually possible. Long wings. Long parallel-sided bill, thinner than HEGU. Imms show 2-tone bill, red-and-black bill spots in older birds. Slightly darker mantle and yellow/green legs, in combination with size and bill shape, are diagnostic in older birds. Extensive black on wing-tips. Younger birds fairly uniformly checkered warm brown (like some HEGU). Focus on size, shape, and upperwing with dark greater coverts and inner primaries. Ad br: medium-gray upperparts, dark iris, red orbital ring, yellow-green legs, red and black on yellow bill. Nonbr: streaking on head strongest on nape. 2nd-s and older: as adult. Juv: all-dark bill soon becomes bicolored (as RBGU and some HEGU). 1st–w: feathers molted in through winter with variable timing and appearance. 1st-s: some get medium-gray adult-like feathers on mantle, others may not show this until reaching 2nd winter.