Vertebrate Zoology - V. M. Konstantinov 2011

Chordates
Terrestrial, or Four-Legged, Vertebrates — Vertebrates with Embryonic Membranes
Class Birds — Subclass Fan-tailed Birds, or True Birds — Superorder Neognathae, or Typical Birds — Order Strigiformes

Taxonomically, owls are far removed from diurnal raptors, with which they share A number of superficial, convergent morphological traits that evolved as adaptations to somewhat similar living conditions. For instance, owls possess a hooked cere-covered beak and sharp, strongly curved talons. However, in connection with their predominantly nocturnal habits, they have developed many distinctive structural and behavioral adaptations.

Their plumage, composed of soft feathers, is very dense yet loose, rendering their flight completely silent. When searching for prey, owls rely primarily on an exceptionally acute sense of Hearing. The ear openings are markedly developed and feature cutaneous folds in front of them that enhance the concentration of sound waves. Their eyes are very large, allowing them to see well even at night, and their heads are extraordinarily mobile, capable of rotating through 270°. The feet, with long toes, serve as the sole instrument for grasping prey; the outer (fourth) toe is reversible and can be swung backward to oppose the two front toes. Unlike diurnal birds of prey, owls lack a crop. They are distributed worldwide. The total number of species is approximately 205, with 11 genera and 17 species represented in Russia. Clutch sizes vary among species from 1–2 to 10–18 eggs (most commonly 3–5). Incubation is performed solely by the female, while the male brings her food. Incubation begins with the first egg and lasts for 3–5 weeks. The chicks are altricial. Both parents feed them for 3–6 weeks.

The snowy owl (Nyctea scandiaca) is distinguished by its large size and almost entirely white plumage. It nests in the tundra, migrating somewhat southward in winter, and successfully hunts in full daylight.

The Eurasian eagle-owl (Bubo bubo) is our largest owl (body mass up to 4 kg, length 75 cm) and is widely distributed across Russia, with the exception of the tundra zone. It nests on the ground, on cliffs, and less frequently in trees. The clutch contains 2–3 eggs. It hunts at night, and its diet varies seasonally and geographically. In winter in Central Asia, it preys mainly on birds (such as ducks and coots). In summer in the south, it feeds on hares, jerboas, and hedgehogs, though mouse-like rodents form the staple of its diet, supplemented in certain years by hares.

The long-eared owl (Asio otus) is of medium size (body length 35–40 cm, mass 220–430 g) with well-developed ear tufts. It is distributed across the southern and temperate zones of Russia, inhabiting woodlots and forest edges. It nests in tree hollows, in old nests of other birds, or on the ground. The clutch consists of 3–7 eggs. It hunts at night and feeds almost exclusively on mouse-like rodents, only occasionally catching birds (see Fig. 147).

Owlets of the genera Athene and Glaucidium are small owls (wing length 9–15 cm) with a large, broad HEAD and no ear tufts.

The tawny owl (Strix aluco) is one of our most common owls. It is a large bird, about the size of a crow (body mass 450–600 g, length 37–39 cm), lacking ear tufts. It is distributed throughout the forest zone of Europe, Siberia, the Caucasus, and Central Asia. It is a sedentary and relatively sluggish bird, nesting in tree hollows and on trees. It hunts at night.

As evident from all the data presented, owls feed primarily on mouse-like rodents, which often cause damage to agriculture. The ecological value of owls is further enhanced by the fact that they hunt at night when other birds of prey are resting.

Many species have become rare, and 21 species of owls are currently listed on the IUCN Red List.