The Owls form almost as natural an order as the Parrots, and occupy, both in external characters and in their anatomy, a position between the Psittaci and the Accipitres. Although long regarded as a suborder of the Accipitrine or Raptorial birds, they have of late years been generally placed in a distinct ordinal group.
Amongst the more conspicuous characters are the reversible outer toe, the position of the eyes, which are always directed forward and are generally very large, and the short curved and hooked bill, the basal portion covered with a cere in which the nostrils are pierced, the cere being almost entirely concealed by the mass of bristly feathers on the lores and forehead. In most of the genera the head is large and the facial portion covered with feathers radiating from the eyes and forming the facial disk, the outer margin of which is surrounded by a ruff of close-textured feathers forming a conspicuous border. From the margin of the ruff above the eyes there arise in many Owls aigrettes of lengthened feathers, known also as horns or ear-tufts, the last term being incorrect. The plumage is soft, and the Coloration generally brown or rufous, the feathers in some genera being delicately vermiculated or stippled as in the Caprimulgi.
The feet are strong and furnished with short claws; a hallux is always present. The oil-gland is nude. The spinal feather-tract is well defined on the neck. There is no aftershaft. There are always 11 primaries. The flexor longus hallucis leads to the hallux, and the flexor perforans digitorum to the remaining three-digits, but the two tendons are united by a broad vinculum. There is no ambiens muscle; the femoro-caudal is present, but the accessory femoro-caudal and the semitendinosus and accessory semitendinosus are wanting. Basipterygoid processes are present and the palate is desmognathous, or, according to Gadow, schizognathous with a desmognathous tendency. Both carotids are present and the caeca are large. Cervical vertebras 14. All Owls lay white and very round eggs, and the majority, like Parrots and most Picarian birds, take possession of a hole or hollow in the trunk or a branch of a tree for the purpose of nidification, and use little or no lining. A few lay their eggs in holes amongst rocks, or on the ground, or in abandoned nests of other birds, and some are said to build their own nests of sticks. The young are hatched helpless and covered with down. The female, in some Owls, exceeds the male in size, but not to the degree that prevails amongst Accipitrine birds, whilst in many cases there is no difference in size between the sexes.
Owls are nocturnal or crepuscular and carnivorous and live for the most part on mammals, on other birds, or on reptiles; a few subsist on fish, and many of the smaller kinds on insects. The indigestible portions of the food—bones, hair, scales, &c.—are disgorged as pellets. It is not an uncommon thing to find masses of small bones in a hollow tree, thus accumulated.
The Owls comprise two families, both Indian. These families are well distinguished by osteological characters, but present no external differences of any importance.
Skull long and narrow, breadth much less than 2/3 of length; furcula united to keel of sternum …………………………..Strigidae, p. 264.
Skull broad, generally about f of length ; furcula not in contact with keel of sternum…………………………..Asionidae, p. 267.