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 Irruption An irregular mass movement of birds beyond their usual range, often when food runs short. Philopatry The tendency to return to breed at or near the place of birth. Brood parasite A bird that lays its eggs in the nests of other species, which then raise its young. Anting Rubbing ants on the feathers, or lying on an ant nest, probably to control parasites. Kettle A group of raptors or storks circling together in a rising thermal. Mobbing Small birds noisily harassing a predator such as an owl or hawk to drive it away.