Mobbing
The 'attacking' of a potential predator by small birds, usually in groups. Its function is presumably to confuse the predator. Not only genuine predators are mobbed but also some birds which have similar flight shapes to certain types of raptor, such as the Grey Heron Ardea cinerea and the Cuckoo Cuculus canorus.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver