nest, structure for the reception and incubation of the eggs of birds, reptiles, insects, and some fish or for the parturition of mammals, and also for the care of the young during their period of helplessness. Chimpanzees, orangutan, and gorillas build nests to sleep in each night. Birds are the chief nest builders, exhibiting great variety and ingenuity among the different species. The type of nest depends on the environment and the condition of the young when hatched. Altricial birds, whose young are generally blind, naked, and helpless on hatching, usually build higher and more elaborate nests than do precocial birds, whose young have a downy covering and are able to move about and feed themselves soon after emerging from the egg. Most sea birds, shore birds, and game birds do not build real nests but lay their eggs directly on a rocky ledge or in a shallow depression scooped out of the earth or sand. Woodpeckers and parrots nest inside hollow trees, as do the Old World hornbills; the male hornbill seals the female into the cavity, leaving an aperture only large enough for him to feed her as she incubates the eggs. Sand martins and kingfishers dig tunnels into shore banks, with enlarged nesting chambers at the ends. The stork's nest is a simple platform of sticks, and the eagle's aerie, built in tree tops or on cliffs, may be 5 to 12 ft (1.5–3.7 m) in diameter; both birds add to their nests each year. As a general rule, the smaller the bird the more elaborate is the nest. Among passerine (perching) birds the male usually selects the feeding and nesting territory, while the female chooses the nest site. In many species the duties of nest building and incubating are shared. The nest is usually bowl-shaped and composed of twigs, grass, leaves, and (when available) bits of cloth and string; thrushes line their nests with clay. Intricately woven, pendent, arboreal nests give the American oriole its alternate name, hangnest; the Old World weaverbirds' nests are similar, with one species building immense communal structures housing up to 600 birds. Swallows, ovenbirds, and flamingos build nests of mud cemented with saliva, and an Oriental swift builds its nest entirely of a salivary secretion (used to make bird's-nest soup by the Chinese). The turkeylike megapode, or mound bird, of Australia leaves its eggs in a pile of decaying vegetation, which provides the heat to incubate them; it is the only bird to share this nesting method with the reptiles. Among the insects, ants, bees, and wasps are well known for their nests. Some fish (e.g., the stickleback) build nests of weeds. Most rodents (e.g., mice and squirrels) are nesters; rabbits line their nests with down, as do ducks and geese. The den or lair of the larger mammals (e.g., wolves and lions) serves the same function as a nest.
See P. Goodfellow, Avian Architecture (2011).