The Bonaparte's Gull, Chroicocephalus philadelphia, is a small gull.

Adults are 31-34 cm long with a 79-84 cm wingspan. They have a black hood and a short thin dark bill. The body is mainly white with pale grey back and upper wings. The underwing is pale and the wing tips are dark. They have orange legs. In winter, the head is white.

In their first summer, the appearance of Bonaparte's Gull is similar to that in its first winter, but paler due to wear. Fewer than 5% of Bonaparte's Gulls acquire a dark hood in their first summer, and on those that do, the hood is duller than on breeding adults.

Their breeding habitat is near bogs or lakes in coniferous forest across western Canada and Alaska. They nest in conifers, sometimes on the ground.

They are migratory and most move east or west to coastal waters, also the Great Lakes. They are rare vagrants to western Europe, where they usually associate with the somewhat larger Black-headed Gulls.

These birds forage in flight or pick up objects while swimming or wading. They mainly eat insects, crustaceans and fish. Unlike some other gulls, this bird rarely scavenges.

They are graceful in flight, more like terns. They were named after Prince Charles Lucien Bonaparte, a zoologist and nephew of Napoleon.

Formerly known as Larus philadelphia, the Bonaparte's Gull was moved to the genus Chroicocephalus by the American Ornithologists' Union in July, 2008.