This gull has narrow wings, a slender, black, pin-like bill, and pink legs. It has a light slate-gray back, with a black line down the trailing edge of the outer wing, and a white belly. The leading edges on the upper surfaces of the outer wing are white. In breeding plumage, the adult has a black head and an incomplete white eye-ring. Non-breeding adults lack the black hood. The adult’s head is white with dark smudges and a dark ear-spot. Dark markings on the wings of the juvenile look like a narrow, dark ‘M’ across its back in flight. Bonaparte’s Gulls reach maturity when they are two years old.
Bonaparte’s Gulls generally forage in single-species flocks, but are commonly seen in the same spot as many other gull species. They do not frequent garbage dumps, but often feed at sewage lagoons. They use a variety of foraging strategies, including dropping into the water from the air, picking up items while swimming or wading, and catching insects in mid-air. They often occur in tight feeding aggregations with peak numbers corresponding closely to density of fish. They are subject to kleptoparasitism by Parasitic Jaegers.
Bonaparte’s Gulls breed at the edge of the northern forest in areas with coniferous trees adjacent to lakes, marshes, or bogs. During migration and in winter, they frequent bodies of water, including rivers, lakes, sewage ponds, estuaries, and open ocean.
Numbers appear to be stable. The nesting grounds of Bonaparte’s Gulls are very remote, and thus they have not been harmed by human disturbance.
Rare vagrant in Europe, mostly to Brittain and Ireland. Between 1990 and 2000 several observations in iceland.
On nesting grounds, insects are the primary prey of the Bonaparte’s Gull. In coastal areas during the non-breeding season, fish, krill and other marine creatures make up a large portion of their diet. In a study of the effect of fish-eating birds on Chinook salmon fry, Bonaparte’s Gulls were the most efficient predators of the ten species studied.
This species has a large range, with an estimated global Extent of Occurrence of 4,300,000 km². It has a large global population estimated to be 260,000-530,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]
Bonaparte’s Gulls nest singly or in loose colonies located on islands or lakeshores. They are unusual among the gulls in that they usually nest in trees rather than on the ground. Spruce is the most common choice for nesting, and nests are built of small twigs, moss, lichen, grass, and other herbaceous vegetation. Nests are typically situated 4-15 feet off the ground on a horizontal branch. The female lays three eggs, which both sexes incubate for about 24 days. Both parents help feed the young. Fledging age is not known.
Migratory. From inland breeding grounds in conifer zone of Alaska and west-central Canada, migrates south to Pacific coast and south-east (across James Bay, Great lakes, and inner Gulf of St Lawrence) to Atlantic. Winters on coasts from Washington (occasionally southern British Columbia) to northern Mexico, from New England (also lakes Ontario and Erie in milder seasons) to Florida, in Gulf of Mexico, and (in low numbers) in West Indies.
Occurrences in Europe perhaps linked to strong south-east movement across Canada in autumn. Records are spread throughout the year, consistent with wintering and summering following autumn or early winter vagrancy.
- spanwidth min.: 90 cm
- spanwidth max.: 100 cm
- size min.: 28 cm
- size max.: 30 cm
- incubation min.: 23 days
- incubation max.: 25 days
- fledging min.: 0 days
- fledging max.: 0 days
- broods 1
- eggs min.: 2
- eggs max.: 4
- Conservation Status