Bird of the Month: Bonaparte's Gull

By Andy McCormick

Scientific Name: Chroicocephalus philadelphia

Length 13.5 in

Wingspan 33 in

Weight 7 oz

AOU Band code BOGU

“The Bonaparte’s has a graceful, buoyant flight, which is rather ternlike” (Alderfer). It can easily be overlooked if it is flying with terms. It is one of the smallest North American gulls and is quite attractive in both breeding and winter plumage. In breeding plumage it has a slaty black hood, and red legs. In winter the hood molts to white and a round, black dot remains near the ear. In all plumages adults have a small, black bill. Conspicuous in flight is the flash of a triangular wedge of white along the leading edge of the outer part of the wing.

The genus name Chroicocephalus is from the Greek chroma, color, and cephalus, head (Wikipedia) referring to the black hood. Following mitochondrial studies the American Ornithological Union moved Bonaparte’Gull in 2008 to Chroicocephalus which contains 13 species of gulls. This gull was named after Charles Lucien Bonaparte, a nephew of Napoleon Bonaparte and an ornithologist who spent about five years in America. The gull was named for him by George Ord of Philadelphia who found the gull in that city (Mearns).

The Bonaparte’s is fully migratory and will move through Washington in April and May on its way to nesting grounds in the boreal forest. Although it will migrate in large numbers sometimes into the thousands at a time, it nests in small, remote, scattered colonies in trees. The nest is usually an open platform of sticks lined with moss and grass built on a horizontal branch in a spruce or other conifer (Kaufman). Because Bonaparte’s Gulls nest in such a remote environment we have little knowledge of their breeding habits.

Usually three olive to buff colored eggs are deposited and both parents are thought to incubate them. The young hatch in about 24 days. The diet in this northern region consists mostly of insects, which both parents bring to the nest (Kaufman). The time needed before the nestlings’ first flight is not known.

Although Bonaparte’s Gulls can be seen anywhere in Washington in winter, they spend most of their time near water. Those that winter in Washington congregate around Puget Sound and the Pacific Coast and can often be seen in the company of Red-throated Loons, Western Grebes, and Red-breasted Mergansers (Dunne). They feed on forage fish, crustaceans, marine worms and insects, foraging by plunging into the water or dipping from the surface (Burger and Gochfeld). Congregations of Bonaparte’s Gulls are often found near upwellings at sea, and along tidal rips, sewage outfalls, and lagoons. Unlike the larger gulls they are rarely found foraging at landfills.

Population numbers appear to be stable and there is no conservation management plan. They are not considered pests and have not been managed as one (Burger and Gochfeld).