It occurs in a variety of habitats including coasts, lakes, rivers, parking lots and garbage dumps.

This gull was first described as a new species in 1862 by Elliott Coues based on a series of specimens from the Smithsonian Institution.

The species name smithsonianus commemorates English chemist James Smithson whose £100,000 bequest enabled the foundation of the institution that bears his name.

[3] Several authorities such as the Association of European Rarities Committees and British Ornithologists' Union now recognize it as a separate species.

[4][needs update] It is a heavily built large gull with a long powerful bill, full chest and sloping forehead.

[7] Breeding adults have a white head, rump, tail, and underparts and a pale gray back and upperwings.

[8] The more-intense "keow" is a loud yet short alarm call that is both identifying and communicative of impending danger.

The "choking" call is produced during courtship displays, nest construction or territorial disputes, accompanied by a rapid bobbing of the head in a direction of interest.

[11] First-winter European birds have more checkered upperparts, more streaked underparts, and a paler rump and base to the tail.

Birds are present all year in southern Alaska, the Great Lakes, and the north-east USA, but most birds winter to the south of the breeding range as far as Mexico with small numbers reaching Hawaii, Central America and the West Indies.

Food is plucked from the surface of the shore or sea or is caught by dipping underwater or by shallow plunge-diving.

[6] They also feed on clams and mussels by dropping them from a height on hard surfaces such as roads or rocks to break their shells.

They are 72 mm (2.8 in) long and are variable in color with brown markings on a pale blue, olive, or cinnamon background.

[16] It has been observed that some pairs cement a close bond, staying in watchful proximity of each other year-round; Other gulls display more independence, but may take the same mate each spring.