With regard to age, feathers are divisible into two groups: (1) neossoptiles, or feathers of the young birds • at the time of hatching; and (2) teleoptiles, or feathers of later life. The neossoptiles are of two kinds: (1) the pre pent= which immediately precede the contour feathers; and (2) the prepliimuhe which pre cede the down feathers. A further division is made of the pre-pennz into rprotoptiies) and gmesoptiles? •but these are important only to the scientific ornithologist. The are always downy in structure and after a vary ing period they are superseded by the teleoptilee4 In the penguins there are two distinct plumages of neossoptiles one succeeding the other; the second growth beginning before the first is shed. The short calamus of the neessoptile ever be5 comes closed up and is split longitu&nally as it is forced out by the teleoptile and for some time its slender downy barbs are borne on the tip of the new feather. When one generation of teleoptiles succeeds another the old feathers usually drop out but in the emus and casso waries they remain • attached to the tips of the new feathers, just as do the neossoptiles. Neos soptiles are best developed in the birds which run about within a short time after hatching, such as the gallinaceous birds, ducks, sand pipers, etc. In these species the body is thickly and completely covered with down. In the hawks and owls the covering is nearly as thick, but in the latter the neossoptiles grow out for a considerable time after hatching, sometimes completely altering the appearance of the bird. In the snowy owl, for instance, the newly hatched young with the tips of the neossoptiles showing, is pure white, while older ones, in which these feathers are full grown, appear dull gray, owing to the difference in color of the terminal and basal portions of the feathers.
In passerine birds the neossoptiles are not very abundant, while in several groups—notably the woodpeckers where the young are reared in hollowed trees and the kingfishers which bur row in sand banks — the neossoptiles have been entirely suppressed, so that the first coat of feathers on these birds consists of teleoptiles and the young birds are naked until these appear. This is perhaps owing to the protection afforded by the nest to the young, renders the downy covering less necessary. In the mound-builders a still more remarkable con dition prevails. Here the neossoptiles are de veloped but are shed before the bird is hatched and it actually leaves the shell clad in the teleoptiles.
Feathers are not distributed uniformly over the body of a bird as are the hairs of a cat or rabbit, but they are in well-defined groups or areas known as with bare spaces, gapteria) between. In some kinds of birds the apteria are covered with down feathers. The pterylm are of characteristic outlines in differ ent families and are thus of value in deter mining relationships.
It is obvious that the early plumage condi tion of birds is to some degree dependent upon their nesting habits and this must be clearly borne in mind when it is considered in con nection with classification. Thus many appar. ently striking characters will be seen at once to have been very recently acquired.
Following the nestling stage, birds acquire one coat of feathers after another, the frequency of the change depending upon the number of molts. The first teleopule or plum age is generally quite different from that of the adult, is worn for only a few months after the bird leaves the nest, when it is superseded by the plumage of the first winter, in which the characters of the adult generally appear. This
may be retained for a whole year, or It may give way to a nuptial plumage in the early spring, the latter being always the case in birds which are strikingly different in color in sum mer and winter. It is now demonstrated that feathers cannot change their pigment after they are once developed and consequently striking changes are due to molt. There are some par tial exceptions to this, in the case of birds whose plumage undergoes marked wear or abrasion, such as the snow-bunting. In this species the feathers of the back are black at the base, those of the head white, but both are broadly tipped with brown, and as they lie in place brown is the prevailing tint. In early spring the tips become brittle and fall away, leaving the black-and-white basal portions in strong contrast. In the crossbill, as shown by Dr. Dwight, the barbs are red and the barbules gray and in spring the latter fall off, resulting in a material brightening of the plumage.
The relation of the juvenal plumage to that of the adult bird is a matter of much interest, owing to the fact that it usually shows some ancestral characters, and often gives us a clue to the relationship of the species; for example, the 'riling of our robin is spotted like the an cestral thrushes, while the adult has departed widely from this type in its plain rufous breast and slaty back.
In a large number of species the plumages of the male and female differ materially; the lat ter is always the more primitive, and the male generally assumes a dress similar to it for the winter, returning to his brilliant livery on the approach of the nuptial season. Darwin's the ory of sexual selection, which was formerly held to account for the brilliant plumage and wonderful ornamental feathers of male birds is in the light of modern investigations not satis factory, but no acceptable theory has yet been presented. Protective coloration in plumages has received a good deal of attention from Wallace and others, and doubtless the theory in some cases has been unduly elaborated. While protective coloration plays a part in the evolution of plumage it is quite as likely that, for instance, pale desert forms are as much the result of the direct effect of the sun as purely protective development. The protective plum ages of the ptarmigan both in winter and sum mer, and the curious protective or dress acquired by certain ducks in summer when rendered temporarily flightless by their peculiar method of molting, deserve mention in this connection.
Molt varies in extent, may be complete or only partial. That which takes place after the breeding season is always complete; but the spring molt may be complete or reduced to a few feathers only, varying greatly. Molting takes place after a definite plan which differs with the species. In ducks, and certain other water birds, the quills are shed all at once. See PTERYLOGRAPH Y. Consult Chapman, F. M., of Birds of Eastern North Amer ica' (Rev. ed., 1912; pp. 84-96) Dwight, J., (Sequence of Plumages and Moults of the Passerine 'Birds of New York' (in Annals of the New York Academy of Science, Vol. XIII, pp. 73-360, New York Stone, W., The Molting of Birds) (in Proceedings of the Phil adelphia Academy of Natural Sciences, 1896; ' pp. 108-167) Strong, R. M., (The Development of Color in the Definitive Feather' (in Bulle tin of the Museum of Comparative Zoology of Harvard College, Vol. XL, No. 3; Cambridge 1902).
See PLUMMET.