Unique smoky-gray gull with red bill. Breeding adults have a clean white head that blends seamlessly into the gray neck; nonbreeding adults have smudgy dark streaking on the head. Immatures are entirely dark brown with a yellowish or reddish bill with a dark tip. Almost exclusively coastal; usually seen in flocks loafing on beaches or feeding in nearshore waters. Breeds in Mexico mainly in the Gulf of California; migrates as far north as Washington and British Columbia in winter. Overall dark plumage of immatures might recall a dark-morph jaeger; note Heermann's lacks pale wing flashes and never shows pale mottling on the belly or underwings.