A kettle is a group of birds wheeling and circling in the air. The kettle may be composed of several different species at the same time. Nature photographer M. Timothy O'Keefe theorizes that the word derives from the appearance of birds circling tightly in a thermal updraft "like something boiling in a cauldron." Ornithologist Donald Heintzelman has done more than anyone to popularize the term kettle, using the term at least as early as 1970 in his book ''Hawks of New Jersey'' to describe raptor flight, followed by uses in print over four decades. The related terms "cauldron" and "boil" are also heard to describe the same sorts of raptor behavior. Osprey-watcher David Gessner, however, claims a Pennsylvania lowland called the Kettle ("der Kessel" in Pennsylvania Dutch), near

Hawk Mountain Hawk Mountain is a mountain ridge, part of the Blue Mountain Ridge in the Appalachian Mountain chain, located in central-eastern Pennsylvania near Reading and Allentown. The area includes of protected private and public land, including the H ...

, is the source of the term. In some species—e.g., the

terns Terns are seabirds in the family Laridae that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated as a subgroup of the family Laridae which includes gulls and skimmers and consists of ...

of Nantucket—kettling behavior is evidently a way of "staging" a flock in readiness for migration. Pre-migrational

turkey vultures The turkey vulture (''Cathartes aura'') is the most widespread of the New World vultures. One of three species in the genus ''Cathartes'' of the family Cathartidae, the turkey vulture ranges from southern Canada to the southernmost tip of South ...

kettle by the hundreds in the thermals that rise over

Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest by ...

before they venture across the

Strait of Juan de Fuca The Strait of Juan de Fuca (officially named Juan de Fuca Strait in Canada) is a body of water about long that is the Salish Sea's outlet to the Pacific Ocean. The international boundary between Canada and the United States runs down the centre ...

toward Washington State. At Hawk Mountain,

broad-winged hawk The broad-winged hawk (''Buteo platypterus'') is a medium-sized hawk of the genus ''Buteo''. During the summer, some subspecies are distributed over eastern North America, as far west as British Columbia and Texas; they then migrate south to win ...

s form kettles in September before flying south.McWilliams, Gerald M. and Daniel W. Brauning (2000). ''The Birds of Pennsylvania'' Cornell University Press. pp.7-8. Kettling apparently serves as a form of avian communication—an announcement of imminent departure—as well as a way of gaining altitude and conserving strength. Turkey Vultures Hovering

References

Bird behavior Ethology {{ethology-stub