EXTERXAL PARTS OF BIRDS. —FEATHERS. 89- 



ivliidi f)pciirs to young and old in the fall. The duck tribe offer the remarkable case, that 

 they drop their %ring-quills so nearly all at once as to be for some time deprived of the power 

 of flight. It is quite certain that many birds cliange the colors of their plumage I'emarkalily, 

 witliout losing or gaining any feathers, by some process which affects the texture of the feath- 

 ers, such as the shedding of the barbicels and booklets, or its pigmentation ; or by such prticesses 

 cinubined. The male of our bobolink changes from the buff dress of the female to his rich black 

 suit without losing or gaining any feathers. It is diiEeult to lay down any rules of moulting 

 for particular groups of birds, since birds very closely related differ greatly in respect to tlieir 

 clianges of plumage, and the subject has not yet received the attention its interest and impor- 

 tance should claim for it. The physiological processes involved are analognus to those con- 

 cerned in the shedding of the hair of mammals and the casting of the cuticle of rejjtOes. 



Plumage-changes -with Sex, Age, and Season. Aside from any consideration nf the 

 ^vay in which plumage changes, whether by moult or (otherwise, the fact remains tliat most birds 

 of the same species differ more or less from one another according to certain circumstances. The 

 dissmiilarity is not only in ccdoration, though this is the usual and most pronounced tlifference, 

 but also in the degree of development of plumes, — their size, form, and texture. Since young 

 birds are thcise which have not come to sexual vigor ; since breeding recurs at reguL^r periods 

 of the year; and since males and females usually differ in plumage, — nearly all the various 

 dresses worn by different individuals of the same species are correlated with the c.onditions of 

 tlie reproductive system. As the internal generative organs represent of course the essential or 

 primary sexual characters, all those of the Ydumage just indicated may be properly classed as 

 secondary sexual characters. These are of great importance, not only in practical ornithology. 

 Tint as the basis of some of the soundest views that have lieen advanced respecting the evolu- 

 tion of specific characters in this class of animals. The generalizations may be made : tlnit 

 when the sexes are strikingly different in plumage, tlie young at first resemble tlie female; 

 wTien the adults are alike, the young are different from cither; when seasonal changes are great, 

 t!ie young resemble the fall plumage of the parents; and, further, that when the adults of two 

 ndated .species of the same genus are nearly alike, the young are usually intermediate, their 

 specific characters not being fully developed. Specific characters are often to be found only in 

 tlie male, the females of two related species being scarcely distinguishable, though the males 

 may be told apart at a glance. Extraordinary developments of feathers, as to size, shape, and 

 i-nlor, are often confined to one sex, usually the male. The more richly, extensively, or pecu- 

 liarly the male is adorned, tlie simpler the female in comparison, as the peacock and peahen. 

 The ^Vise Man of Late has formulated the several categories of secondary sexual characters, 

 giving the following rules or classes of cases : "1. When the adult male is more beautiful or 

 consfiicuous than the adult femide, the young of lioth sexes in their first plumage closely 

 re.semble the adult female, as ■\^ith the common fowl and peacock; or, as occasionallv 

 occurs, they resemlile her much more closely than they do the adult male. 2. "When the adult 

 fein;ile is more conspicuous than the adult m;ile. as sometimes though rarely occurs [ehieflv 

 with cert^iin birds of prey and snipe-like birds], the young of both sexes in their first plumage 

 resemble the adult male. 3. When the adult male resembles the adult female, the young of 

 both sexes have a peculiar first plmnage of their own, a.s with the robin [usual], i. When the 

 adult male resembles tlie adult female, the young of both sexes in their first plumage resemble 

 tlie adults [unusual]. 5. When the adults of both sexes have a distinct winter and suminiT 

 plumage, whether or not the male differs from the female, the young resemble the adults nf 

 both sexes in their winter dress, or much more rarely in their summer dress, or they resemble 

 the females alone. Or the young may have an intermediate character ; or again they may 

 differ greatly from the adults in both their seasonal pilumages. 6. In some few cases the 

 young in their first plumage differ from each other according to sex ; the young males re- 



