ROOK (O.E. Hr6c, Icel. Hr6kr,1 Swed. Mika, Du. Roek, Gael. Rocas)  , the Corvus frugilegus of ornithology, and through-out a great part of Europe the commonest and best-known of the crow-tribe, belonging to the Passerine family Corvidae . Besides its pre-eminently gregarious habits, which did not escape the notice of Virgil (Georg. i . 382)2 and are so unlike those of nearly every other member of the Corvidae, the rook is at once distinguished from the rest by commonly losing at an early age the feathers from its face, leaving a bare, scabrous and greyish-white skin that is sufficiently visible at some distance . In the comparatively rare cases in which these feathers persist, the rook may be readily known from the black form of crow (q.v.) by the rich purple gloss of its black plumage, especially on the head and neck, the feathers of which are soft and not pointed . In a general way the appearance and manners of the rook are well known, and particularly its habit of forming communities in the breeding-season, which it possesses in a measure beyond that of any other land bird of the northern hemisphere . Yet each of these communities, or rookeries, seems to have some custom intrinsically its own . In a general way the least-known parts of the rook's mode of life are facts relating to its migration and geographical distribution . Though the great majority of rooks in Britain are sedentary or only change their abode to a very limited extent, it is now certain that a very considerable number arrive in or towards autumn, not necessarily to abide, but merely to pass onward, like most other kinds of birds, to winter farther southwards; and, at the same season or even a little earlier, it cannot be doubted that a large proportion of the young of the year migrate in the same direction . As a species the rook on the European continent only resides during the whole year throughout the middle tract of its ordinary range . Farther to the northward, as in Sweden and northern Russia, it is a regular summer-immigrant, while farther to the southward, as in southern France, Spain and most parts of Italy, it is, on the contrary, a regular winter-immigrant . The same is found to be the case in Asia, where it extends eastward as far as the upper Irtish and the Ob . It breeds throughout Turkestan, in the cold weather visiting Afghanistan, Cashmere and the Punjab, and Sir Oliver St John found a rookery of considerable size at Casbin in Persia .

In

Palestine and in lower Egypt it is only a winter-visitant, and H . B . Tristram noticed that it congregates in great numbers about the mosque of Omar in Jerusalem . The same writer (Proc . Zool . Soc., 1864, p . 444; Ibis, 1866, pp . 68, 69) considered the Palestine rook entitled to specific distinction as Corvus Agricola . The rook of China has also been described as a distinct species, C. pastinator (Proc . Zool . Soc., 1845, p . 1) from having the feathers of its face only partially deciduous .