HomeGlossary Behaviour Lek A display ground where males gather and perform to attract females. Grouse, manakins, cocks-of-the-rock and many birds-of-paradise breed at leks. BehaviourRelated termsFull glossary Brood parasite A bird that lays its eggs in the nests of other species, which then raise its young. Philopatry The tendency to return to breed at or near the place of birth. Irruption An irregular mass movement of birds beyond their usual range, often when food runs short. Fallout Large numbers of migrants landing at once, usually when bad weather meets a migration. Kettle A group of raptors or storks circling together in a rising thermal. Anting Rubbing ants on the feathers, or lying on an ant nest, probably to control parasites.