Weaver birds, also known as weaver finches, get their name because of their elaborately woven nests (the most elaborate of any birds'), though some are notable for their selective parasitic nesting habits. The nests vary in size, shape, material used, and construction techniques from species to species. Materials used for building nests include fine leaf-fibers, grass, and twigs. Many species weave very fine nests using thin strands of leaf fiber, though some, like the buffalo-weavers, form massive untidy stick nests in their colonies, which may have spherical woven nests within. The sparrow weavers of Africa build apartment-house nests, in which 100 to 300 pairs have separate flask-shaped chambers entered by tubes at the bottom. Most species weave nests that have narrow entrances, facing downward.
Many (but not all) species of weavers are gregarious birds that breed colonially. The birds build their nests together for protection, often several to a branch. Usually the male birds weave the nests and use them as a form of display to lure prospective females. The weaver bird colonies may be found close to water bodies. They sometimes cause crop damage, notably the Red-billed Quelea, reputed to be the world's most numerous bird.