Owls have large forward-facing eyes and ear-holes, a hawk-like beak, a flat face, and usually a conspicuous circle of feathers, a facial disc, around each eye. Although owls have binocular vision, their large eyes are fixed in their sockets, as with other birds, and they must turn their entire head to change views. Most birds of prey sport eyes on the sides of their heads, but the stereoscopic nature of the owl's forward-facing eyes permits a greater sense of depth perception necessary for low-light hunting.
Owls are farsighted and are unable to see anything clearly within a few centimeters of their eyes. Caught prey can be felt by owls with the use of filoplumes, which are small hair-like feathers on the beak and feet that act as "feelers". Their far vision, particularly in low light, is exceptionally good. Contrary to popular myth, an owl cannot turn its head completely backwards. It can turn its head 135 degrees in either direction; it can thus look behind its own shoulders, with a total 270-degree field of view.
The smallest owl is the Elf Owl (Micrathene whitneyi), at as little as 31 g (1.1 oz) and 13.5cm (5.3 inches). Some of the pygmy owls are scarcely larger. The largest owls are two of the eagle owls; the Eurasian Eagle Owl (Bubo bubo) and Blakiston's Fish Owl (Bubo blakistoni)—which may reach a size of 60 - 71cm (28.4 in) long, have a wingspan of almost 2 m (6.6 ft), and an average weight of nearly 4.5kg (10 lb).
Different species of owls make different sounds; the wide range of calls aids owls in finding mates or announcing their presence to potential competitors, and also aids ornithologists and birders in locating these birds and recognizing species. The facial disc helps to funnel the sound of prey to their ears. In many species, these are placed asymmetrically, for better directional location.[verification needed]
Owl eggs are usually white and almost spherical, and range in number from a few to a dozen, depending on species. Eggs are laid at intervals of 1 to 3 days and do not hatch at the same time. This accounts for the wide variation in the size of sibling nestlings. Owls do not construct nests, but rather look for a sheltered nesting site or an abandoned nest in trees, underground burrows, or in buildings, barns and caves.
