Fig. 206.—The Rook. (× ¹⁄₁₀.)
One of the most interesting features of rook-ways is the habit of living in organised communities.[24] It is true that a primitive form of social life is found among swallows, martins, and (in winter) larks, reminding us of the gregarious habits of the rabbit ([Chapter XII.]) among mammals; but a rook-society is rather to be compared with the pack-life of the wild dogs ([p. 252]), which depends for its integrity upon the observance of certain rules of conduct by its members. Naturalists have long known that such a code of laws is in force in every rookery, but what these laws are we do not fully understand. Here is a profitable and interesting field of observation for the student. It has sometimes been observed that certain birds are prevented by the rest from building until the nests already commenced are finished, and cases have been known of birds being expelled from the rookery, or even put to death, after a consultation or “trial,” presumably for some breach of law. On the other hand, it must be admitted that rooks are generally arrant thieves, not scrupling to rob their neighbours’ nests of building-materials to save themselves trouble. They are also very quarrelsome.
Fig. 207.—Rooks’ Nests in Trees.
The nests are built on high trees ([Fig. 207]); they are composed of sticks and turf, and are lined with moss and soft grass. As each of several adjacent trees often contains a large number of nests, a sort of rook-town called a “rookery” is formed. This is added to from year to year, as the number of the birds increases. During the summer the rookery forms the headquarters of the community, but about August or September, before the leaves are shed, the birds leave their nests, to spend the winter in thicker or evergreen woods, often at some distance. At intervals during the winter they revisit their spring nests. They come back to the rookery in February or March, and at once set about repairing old nests or building new ones. The male bird begins to feed the female even before the bluish-green eggs are laid, and is a pattern of domestic virtue throughout the period of incubation. For some time after hatching, the young birds are fed by the parents. Rooks feed on the ground in flocks, a few birds remaining behind in the trees as sentinels to give the alarm when danger threatens. The food consists very largely of the larvae of injurious insects, especially the grubs of the cockchafer beetle, and although the birds undoubtedly eat corn and other young crops, they do far more good than harm.
Other birds of the crow family.—The crow, raven, jackdaw, magpie, and jay are so similar in many respects to the rook and to each other that naturalists include them all in one group, which they call the crow family.
The passerine order.—The families of the birds hitherto considered in this chapter, with the flycatchers, wrens, chats, tits, finches, linnets, starlings, etc., are further grouped together to form what is called an order. The order which consists of these families derives its name passerine from the sparrow[25] ([Fig. 208]), perhaps the commonest of the birds included in it. It is probably in this order that bird structure attains its most perfect development. Again, the birds of the crow family are generally considered to stand at the head of the order; if this view is correct, rooks must be regarded as occupying, among birds, a position which roughly corresponds to man’s place in the class of mammals.
Passerine birds are nearly all singers, and their toes are generally adapted for perching. They feed upon insects, seeds (especially the seeds of grasses), and soft fruit. Their beaks vary in form according to the nature of the food upon which they most depend, as is well shown by the soft, widely opening bills of the swallows, the strong but slender beaks of the thrushes, larks, and crows, and the short, hard beaks of such seed-eaters as the canary, sparrow, and other finches. Birds which are exclusively, or almost exclusively, insectivorous are compelled to migrate to warmer countries to obtain food during the winter. The eggs of passerine birds are usually coloured or spotted, and the young birds are hatched in a helpless and almost naked condition, being carefully tended and fed by both parents until they are able to fend for themselves. A few familiar birds of other orders will now be briefly considered.