great grey owl
specimen showing the extent of the body plumage, Zoological Museum, Copenhagen
While typical owls (hereafter referred to simply as owls) vary greatly in size, with the smallest species, the
elf owl, being a hundredth the size of the largest, the
Eurasian eagle-owl and
Blakiston's fish owl, owls generally share an extremely similar body plan.
 They tend to have large heads, short tails, cryptic
plumage, and round facial discs around the eyes. The family is generally
arboreal (with a few exceptions like the
burrowing owl) and obtain their food on the wing. The wings are large, broad, rounded, and long. As is the case with most
birds of prey, in many owl species
females are larger than males.
Because of their
nocturnal habits, they tend not to exhibit
sexual dimorphism in their plumage. The feathers are soft and the base of each is downy, allowing for silent flight. The toes and tarsi are feathered in some species, and more so in species at higher latitudes.
 Numerous species of owls in the genus
Glaucidium and the
northern hawk-owl have eye patches on the backs of their heads, apparently to convince other birds they are being watched at all times. Numerous nocturnal species have ear-tufts, feathers on the sides of the head that are thought to have a
camouflage function, breaking up the outline of a roosting bird. The feathers of the
facial disc are arranged in order to increase sound delivered to the ears. Hearing in owls is highly sensitive and the ears are asymmetrical allowing the owl to localise a sound in multiple directions. In addition to hearing, owls have massive eyes relative to their body size. Contrary to popular belief, however, owls cannot see well in extreme dark and are able to see well in the day.