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Bonaparte's Gulls are small, slender gulls. Except for the fact that males are a bit bigger and heavier than females, the two sexes are identical. Both sexes have different plumages during the breeding season and in eclipse. In breeding plumage, apart from thin partial white eye-rings, Bonaparte's Gulls have a near-black, dark-chocolate-coloured head. The short neck, the entire front and the rump are white. Only the mantle and wings are light-grey, with white outer primaries and black tips on the primary flight feathers. The white tail has a black terminal band on the upperside. The short bill is black. In eclipse they loose their black cap, leaving just two black spots on either side of the head, above and behind the eyes, with the spots above the eyes being very inconspicuous. In all seasons the wings protrude beyond the end of the tail. The irises are dark. The short legs and feet are pink in and orange-pink during the breeding season. First-winter Bonaparte's Gulls resemble adults in eclipse plumage, but with dark centres to the wing feathers. Juveniles have brownish tints on the head and on the wing feathers.

Twitcher's tip

The easiest way of telling Bonaparte's Gulls apart from Black-headed Gulls is by the colour of the bill (Bonaparte's Gull has a black bill) and by the length of the legs (Bonaparte's Gull has short legs).

The overall distribution of this species can be assessed, and specific locations where birds have been spotted can be found, based on individual sighting reports submitted by birdwatchers to ebird.org .

The global distribution of Bonaparte's Gull is available HERE .

Bonaparte's Gulls are a migratory species. Their core range is the North-American continent. Their breeding grounds lie in central and western Canada and in Alaska, while they overwinter partly in coastal areas (in the West of the continent they are found ONLY along the coastline, from Washington State, USA, in the North to Cabo Corrientes, Mexico, in the South. Along the East coast of the continent they overwinter all along the coastline from Maine, USA, in the North, to Florida, USA, Cuba, and northern Mexico in the South. Bonaparte's Gulls overwinter also inland, from South of the Great Lakes into the Mississippi/Missouri catchment and all the southern states from Texas to the Carolinas. For details see, e.g., Wikipedia .

In Europe, Bonaparte's Gulls are found only as vagrants, with a few records per year from the British isles and rare appearances also along the West coast of Iberia. They visit Europe only outside the breeding season and are therefore always seen in non-breeding plumage.

G. Pinelas reports finding Bonaparte's Gull at Praia da Torre, Oeiras, Lisbon, Portugal, in March 2017. All sighting and photographic information presented on this page has kindly been contributed by G. Pinelas.