BIRDS OF PASSAGE are those birds which spend one part of the year in one country or climate and another part in another, migrating according to the season. No species of bird is known to hibernate (see HIBERNATION); and although many naturalists were at one time inclined to believe in the hibernation of swallows, this opinion has been entirely relinquished, and their annual migrations are fully ascertained. Birds avail themselves of their powers of wing to seek situations adapted for them in respect of temperature and supply of food, and even within the tropics there are birds which migrate as the seasons change from wet to dry, or from dry to wet. See BIRD of PARA DISE. The migration of birds, however, is more generally from n. to s., or from s. to n., in the temperate and colder regions of the globe, as winter passes into summer, or sum mer into winter; and B. of P. are commonly distinguished into summer B. of P. and winter B. of P., as they are summer or winter visitants; but, of course, those which are summer B. of P. in one country are winter B. of P. in another. They breed in the country in which they are summer B. of P. The arrival of summer B. of P. is always among the welcothe signs of advancing spring, and is associated with all that is cheerful and delightful. In winter, flocks of swans, geese, and other water-fowl seek the British coasts and inland lakes and marshes from the frozen north; and at the same time, wood cocks, fieldfares, redwings, and many other birds which breed in more northern regions, regularly appear. Some birds come almost at the same date annually; others are more influenced by the character of the season, as mild or severe: Many sea-fowl are migra to ry, and the inhabitants of St. Kilda and other isles, to whom they are of the greatest
importance, depend with confidence upon their return almost at a particular day. The migrations of pigeons in North America are extraordinary, from the vast numbers of which the migrating flocks consist. See PIGEON. The whole subject of the migration of birds is one of great interest, particularly in reference to the instinct by which they appear to be guided. Birds of migratory species, which have been reared in confine ment, become restless when the season for migration arrives, and in many species the migration seems to be little influenced by the state of the weather. It would seem that the youngest swallows are left behind, to follow the first migrating hosts of their species. The number of 13. of P. is very considerable, nor are they all or mostly birds of long wing and powerful flight, but many short-winged birds are included among them. Some B. of P., as woodcocks, have, however, been found in a very exhausted state after their arrival; and it is to be considered that, both in the old and new world, distant migrations are poK!ble without long flights. Some birds possess such powers of wing-, that they may easily pas§ over wide seas; and the-rapidity of the flight of birds—from 1,0 to 150 rn. an Lour—partly explains the possibility of their migrations between distant parts of the world. It is believed that 13. of P. habitually return to the same localities which they have inhabited in former years, and this seems to lurve been sufficiently established by proof, at least in regard to swallows.