Strigiformes

Strigiformes [‚strij·ə′fȯr‚mēz]

(vertebrate zoology)

The order of birds containing the owls.

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Strigiformes 

(owls), an order of birds resembling Falconiformes in external appearance and biological characteristics but differing from them by the absence of a crop and the presence of long caeca. Owls are crepuscular or nocturnal in habit. The body length ranges from 12.8 cm in the elf owl to 70 cm in the fish owl. The feathers have a long downy base. The soft and loose plumage is most commonly dull brown or reddish; the coloration of males and females is usually similar. The females are larger than the males. Owls have a facial disk of narrow feathers around the eyes. Because the eyes are firmly fixed in the orbits, the field of vision is narrow; the neck’s great mobility, however, ensures a sufficient range of vision. Owls see well in daylight and deep twilight, but their vision is somewhat limited in complete darkness. The openings of the external auditory meatuses are large and usually surrounded by a skin fold; they are often placed asymmetrically, which enables the birds to track prey (for example, rodents) by sound in high grass.

Owls are found throughout the world except in the Antarctic and certain oceanic islands. They inhabit all natural zones, from tundra to desert. Species diversity is most pronounced in forests. There are two families: Strigidae (true owls), with 123 species, and Tytonidae (barn owls), with 11 species. One species of the latter family, the common barn owl (Tyto alba), is found in the USSR.

Although a few species migrate, most owls are sedentary. The birds nest in tree hollows, in the nests of other bird species (for example, crows), on cliffs, on the ground, or in buildings. A clutch usually contains four to six white, almost spherical eggs; some species, for example, the snowy owl (Nyctea scandiaca), lay as many as ten to 14 eggs. One egg at a time is incubated by the female for 25 to 35 days; as a result a nest often contains young of various ages. Owls feed on small mammals (especially rodents), birds, reptiles, and insects. Some species also feed on fishes and crustaceans. The birds swallow their prey whole and regurgitate undigested bones, hair, feathers, and chitin in the form of pellets. Owls are beneficial to agriculture and forestry; they are all protected species.

Eighteen owl species occur in the USSR. Common species are the snowy owl, eagle owl (Bubo bubo), fish owl, hawk owl (Surnia ulula), long-eared owl (Asio otus), short-eared owl (Asio flammeus), tawny owl (Strix aluco), and little owl (Athene noctua).

REFERENCES

Ptitsy Sovetskogo Soiuza, vol. 1. Edited by G. P. Dement’ev and N. A. Gladkov. Moscow, 1951.
Zhizn’ zhivotnykh, vol. 5. Moscow, 1970.

A. I. IVANOV