Young birds have a first plumage, grown during their period of development, that is replaced by a post-juvenile dress of feathers that comes when they are fully grown and able to care for them selves. In most, the flight-feathers remain until the following year, but in some, as the house sparrow (Passer domesticus), the wing and tail-quills are also completely renewed at this first moult.
In most adult birds the moult comes immediately after the close of the breeding season, and in temperate regions occurs in late summer. The birds are thus again in full dress when the time for migration arrives, or, if resident, by the approach of cold weather. Swallows, many shorebirds, and hawks moult during the winter, the two former groups undergoing this process in the winter home after migration.
Most birds have one complete moult annually, which takes place as indicated, at the close of the breeding season. In many, par ticularly among the perching birds there is another moult, partial or complete, through which the bird acquires nuptial plumes. In the bobolink (Dolichonyx orizivorus) and the whinchat (Saxicola rubetra), for example, the body plumage is completely changed in late winter and early spring. Many of the sparrow family, as the cirl bunting (Emberiza cirlus) and the Harris's sparrow (Zono trichia querula), have a partial moult of the feathers about the head that produces bright plumes for the breeding dress.
Change in colour is not necessarily accompanied by moult, as often the tip of a feather may be one colour and the middle portion another. In the throat of the male house sparrow, for example, in autumn and early winter the black throat is obscured by greyish feather tips. As spring arrives the grey tips wear away, so that the black is fully revealed. The most striking change of this type is found in the snow bunting (Plectrophenax nivalis), which is white or light brown above in autumn and winter, but through sloughing of the feather tips becomes entirely black on the back in spring.
Aristotle (384-322 B.c.), the first to discourse connectedly on migration (q.v.), tells in his writings that the crane flies from the steppes of Scythia to the marshlands at the source of the Nile, south of Egypt. He noted migration also in the swan, land-rail, lesser goose, quail, rock-dove and turtle-dove, though he reports that of the last three a few may linger through the winter in pro tected localities. The cuckoo disappeared with the rising of the
dog-star in July. Pliny, in his Natural History, repeats much that had been said by Aristotle, adding that the European blackbird, starlings and thrushes pass to neighbouring countries, while storks and cranes travel to a great distance. There are scattered refer ences to migration in the writings of the middle ages, Olaus Magnus, in 1555, speaking of the migrations of swallows, and Francis Willughby, in 1768, mentioning various migratory birds. In the succeeding century Gilbert White, Thomas Pennant and George Edwards kept regular records of the arrival and departure of birds. Interest in the subject was considerable by the opening of the 19th century, and from that time forward the number of observers and the mass of published information on migration has increased yearly.
Superstitious Beliefs.—Though the migrations of larger birds were understood, as these travelled openly across the spring and autumn skies, the movement of smaller species, that appeared or disappeared under cover of night, so that they were present one day and gone the next, or vice versa, were present suddenly after an absence of several months, was the basis of considerable superstitious belief. It was thought that the smaller species were too weak to travel far, so that, in 174o, J. G. Gmelin was told by the Tatars of K rasnojarsk that each crane carried a corn-crake on j its back in its journeys. In southern Europe the peasantry believe to-day that small birds congregate on the shores of the Mediter ranean, and as opportunity offers flutter on the backs of storks and cranes who carry them across to Africa.
Somewhat more unusual is a belief promulgated in an anony mous tract published in London in 1703 "By a person of Learn ing and Piety," entitled in part "An Essay Towards the Probable Solution of this Question. Whence come the Stork and the Turtle, the Crane, and the Swallow, when they Know and Observe the Appointed Time of their Coming." The author announces a belief that migratory birds travel to the moon, where they pass the winter, the journey in either direction requiring 6o days to compass, during which the author (who, according to Hugh Glad stone, was Charles Moreton, a minister who in late life removed to New England), informs us that they required no food, as they travelled in a rarefied ether.