© S. Seal

A Bonaparte's Gull in first-winter plumage. Note the delicate structure and the fine all-black bill. The wing-pattern is superficially similar to same-aged Black-headed Gull C. ridibundus but differs in:  pale grey bases to inner primaries and primary coverts, creating a cleaner aspect to inner 'hand'; pale and somewhat translucent underside to 'hand'; underwing with neat black margin to entire trailing edge. The slightly greyer hind-neck compared with Black-headed Gull is just evident in the photos.