A bird box is a specially built box designed for birds to make nests in. Bird boxes are often put in back gardens to encourage birds to live there and thus allow the owners to see them. Bird boxes should not be large as the small size allows heat to stay in.
Boxes are usually wooden, though some for birds are made from concrete or mixtures of wood and concrete, called woodcrete. Metal nest boxes are also marketed, but these are generally unsuitable for outdoor use, as they can overheat easily in sunshine.
The majority are cuboid, and many have a sloping roof. Many have a hinged top, side or front to provide access for cleaning, bird ringing or, when used for domesticated species, to give the breeder access to the young. Boxes may either have an entrance hole or be open-fronted. Some nest boxes can be highly decorated and complex. Designs mimicking human house design or other structures are common in some gardens.
Different sizes of nest boxes suit different species of birds with very small boxes attracting wrens and treecreepers and very large ones attracting ducks and owls. The maintenance of bird boxes to remove old nest material and any parasites is important if they are to be successfully re-used. Budgerigars and some other birds raised domestically will not usually mate unless a nest box is available.