Bonaparte's Gull

Status Uncommon transient, rare in summer and winter. Most spring records occur between the beginning of April and mid-May, but first sightings are routine in March (average 28 March, earliest 3 March). The few seen during the summer are probably non-breeding immature birds. The species is much more common in the fall. The first migrants generally arrive at the beginning of August (average 4 August, earliest 22 July), and their passage extends well into November, with stragglers as late as 21 January 1964 at Bon Portage Island, 30 January 1967 at Cape Sable, and all winter in the Halifax area in several recent years. Unlike the Common Black-headed Gull, the majority of our Bonaparte's Gulls are reported from the Northumberland Strait and the Bay of Fundy, on western coasts of the province.

Description Length: 30-36 cm. Adults in summer: Head has a slaty black hood sharply defined against the rest of the plumage; back and wings pearly gray; primaries mostly white, the outermost with a black web and all with black tips, giving the effect of a white wing end bordered with black; rest of plumage white; bill black; legs and feet orange-red. Adults in winter: Similar but head white; shading to gray on sides and back. Immatures: Top of head and nape gray; spot on auriculars dark gray; back pearly gray mottled with grayish brown; rest of wing similar to adult but black of primaries more extensive; tail white, with a narrow, black subterminal band; rest of plumage white; bill mostly dark brown; feet dully flesh-coloured.

Range Breeds from central Alaska and Mackenzie Delta south to central British Columbia and Alberta, and east to James Bay. Winters from Massachusetts to the Caribbean and also along the west coast of Central America.

Remarks This small gull closely resembles the Common Black-headed Gull, from which it may be distinguished by its black (instead of dark red) bill, and by the black markings on the underside of the primaries, which are confined to a narrow black border along the tips of those feathers.

The immediate destination of most fall migrants in our area is Head Harbour Passage in southern New Brunswick, where very large numbers of Bonaparte's Gulls are to be found from August to October, feeding on swarms of euphausiid shrimps. These birds reach the Maritime Provinces after a long overland migration from their nearest breeding area, in northwestern Ontario. The shrimps eaten after breeding season replenish the gulls' fat reserves before the birds continue on their southward journey.