Kettle (birds)

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.

[2] The related terms "cauldron" and "boil" are also heard to describe the same sorts of raptor behavior.

[3] In some species—e.g., the terns of Nantucket—kettling behavior is evidently a way of "staging" a flock in readiness for migration.

[4][5] Pre-migrational turkey vultures kettle by the hundreds in the thermals that rise over Vancouver Island before they venture across the Strait of Juan de Fuca toward Washington State.

[7] 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.