Bonaparte's Gull

Bonaparte's Gull
Bonaparte's Gulls are unusual among North American gulls because they typically build their nests in trees rather than on the ground.

The breeding range of the Bonaparte's Gull extends across northern North America from western Alaska to the Hudson Bay. The species' breeding biology is poorly known. In the spruce and fir trees of the boreal forests, Bonaparte's Gulls build shallow nests of small sticks and twigs, lined with grasses and moss. Nests are usually between 4 and 20 feet above the ground on a horizontal branch. Bonaparte's Gulls may nest as isolated pairs or in small colonies, typically near or over water. Two to four blotched buffy brown eggs hatch after about three and a half weeks. Both parents take care of the nestlings, which begin to leave the nest after one week.

During the breeding season, while on inland lakes and ponds, Bonaparte's Gulls feed mostly on insects picked from the surface of water or from rotting vegetation along the shoreline. In their winter habitat along the Atlantic and Pacific coasts and the Gulf of Mexico, Bonaparte's Gulls feed on small fishes, crustaceans, marine worms, and other invertebrates. They forage by flying over the water's surface with dangling feet, picking small items off the water while swimming, or making shallow dives.
Bonaparte's Gull Range Map

In the fall, Bonaparte's Gulls move along rivers and lakes toward the oceans. Loose flocks may coalesce into huge aggregations. As many 60,000 have been observed at Niagara Falls in early winter. Flocks travel from place to place in response to food availability. During migration they use nearly any body of water including coastal estuaries, rivers, lakes, and sewage treatment ponds. Spring migration is very early, beginning in March. By May, Bonaparte's Gulls have returned to their breeding grounds in the North, sometimes while the snow still lingers.

Description: The Bonaparte's Gull is the smallest North American gull except for the uncommon Little Gull. The small size (12"-14"), and light buoyant flight of Bonaparte's Gulls are reminiscent of terns. Summer adults have black heads, gray mantles and white underparts and tail. The wings show white outer primaries with black trailing edges. The bill is slender and black. The legs and feet are reddish-orange. In winter, the black head becomes white with a dark round spot behind the eye.

Juveniles show the dark ear spot on the head. They have brown on the mantle, scapulars and sides of the breast. The tail is white with a black terminal band. The legs are pale pinkish. By late September, young birds have molted into the first winter plumage, characterized by a narrow dark bar on the upperwings, a dark leading edge to the primaries, which together form an "M" across the upper surface of the wings. They lose the juvenile's brown but retain the terminal band on the tail. In their first summer, they begin to show a dark hood, and the "M" pattern on the wings begins to fade through wear. Bonaparte's Gulls attain adult winter plumage in their second year.