An owl is a type of bird, belonging to the order Strigiformes.
Owls are adapted for nocturnal behaviour, and possess greatly enhanced eyesight and hearing, and the ability to fly silently.
Owls have a unique appearance amongst birds as a result of their nocturnal adaptations. They have large heads, which hold very large eyes compared to those of other birds. The face is surrounded by a disc of stiff feathers, called the facial disc, which acts in a similar manner to a parabolic reflector, focusing sounds that hit it toward the ears.
The ears of owls are not visible, but are nonetheless a very important feature for some owls. The ears are located under the feathers at the left and right sides of the facial disc.
Several owls have a pair of feathery tufts at the top of the head, which are sometimes called 'ears', but they are unrelated to the true ears and have no function in hearing. It is believed that the tufts are there to break up the owl's shape and improve its camouflage.
The beak of an owl is largely hidden under the facial disk, but can open very wide. Several owls swallow their food (normally rodents) whole, and allow their stomach to digest it before regurgitating the indigestible pieces, such as bones, fur, or insect exoskeletons, as a pellet of waste. This is known as casting. Some people collect owl pellets and dissect them to see what the owls have been eating.
Owls have thick, soft plumage, which gives them a fat, fluffy appearance, although they are actually fairly scrawny underneath the coat of feathers. They are generally cryptically coloured.
They have long, broad wings, which allow them to glide slowly. The leading edge of the wing has feathers which deaden the noise of the owl's wingflaps, allowing it to fly silently (although with a loss of efficiency).
Owls are known for their ability to see in extremely poor light, and for their highly sensitive hearing. No owl can see in total darkness, although it has been shown that at least the barn owl can hunt by sound alone.
Owls have highly mobile necks, and can turn their heads round more than three-quarters of a circle. (Although the ability to turn the head through extreme angles is present in most birds, owls are most famous for it.) This offsets the problem of the owl's limited field of vision; its eyes are pointed forward (allowing for binocular vision) and fixed in their sockets.