any of a number of small African birds of the family Ploceidae (q.v.; order Passeriformes) that are extremely gregarious. This name is given particularly to Philetairus socius, which makes an “apartment house” in a tree: dozens of pairs of these little black-chinned birds cooperate year-round to maintain a thatchlike roof over the colony, which may contain 300 chambers (one per pair); the roof may be 7.5 metres (25 feet) wide and 1.5 m high. Each cluster of chambers has a common tunnel entrance from the “basement.”