The barn owl (Tyto alba) is the most widely distributed species of owl, and one of the most widespread of all birds. It is also referred to as the common barn owl, to distinguish it from other species in the barn owl family Tytonidae. These form one of two main lineages of living owls, the other being the typical owls (Strigidae). T. alba is found almost everywhere in the world except polar and desert regions, Asia north of the Alpide belt, most of Indonesia and some Pacific islands.
There is considerable variation between the sizes and colouring of the approximately 28 subspecies but most are between 33 and 39 cm (13 and 15 in) in length with wingspans ranging from 80 to 95 cm (31 to 37 in). The back is some shade of grey or brown, the underparts vary from white to brown, sometimes with some dark speckling. The face is characteristically heart-shaped and is white in most species. This owl does not hoot, but utters an eerie, drawn-out shriek.
The barn owl is known by many common names which mostly refer to its pale colouring or silent flight. It is nocturnal over most of its range but in Britain and some Pacific islands, it also hunts by day. Barn owls specialize in hunting animals on the ground and nearly all of their food consists of small mammals which they locate by sound. Breeding takes place at varying times of year according to locality with a clutch averaging about four eggs, but occasionally more than double this number, laid in a nest in a hollow tree, old building or fissure in a cliff. When numbers of small prey are readily available, barn owl populations can expand rapidly, and globally the bird is considered to be of least conservation concern. However, some subspecies with restricted ranges are more threatened.