EXTERNAL PARTS OF BIRDS. — FEATHERS. 95 



Peacock and Peahen. The Wise Man of Late has formulated several categories of secondary 

 sexual characters, giving the following rules or classes of cases : "1. When the adult male is 

 more beautiful or conspicuous than the adult female, the young of both sexes in their first 

 plumage closely resemble the adult female, as with the common Fowl and Peacock ; or, as occa- 

 sionally occurs, they resemble her much more closely than they do the adult male. 2. When 

 the adult female is more conspicuous than the adult male, as sometimes though rarely occurs 

 [chiefly with certain 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 fem.ale, the 

 young of both sexes have a peculiar first plumage of their own, as with the Robin [usual]. 

 4. When the adult male resembles the adult female, the young of both sexes in their first 

 plumage resemble the adults [unusual]. 5. When the adults of both sexes have a distinct 

 winter and summer plumage, whether or not the male differs from the fenuile, the young re- 

 semble the adults of 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 plumages. 6. In 

 some few cases the young in their first plumage differ from each other according to sex ; the 

 young males resembling more or less closely the adult males, and the young females more or 

 less closely the adult females." — (Darwin, Desc. of Man, ed. 1881, p. 466.) 



Summary of Secondary Sexual Characters of Birds. — The temptation to give the 

 conclusion of the whole matter in Darwin's own words, summary of his views of Sexual Selec- 

 tion as so important a factor in Natural Selection, need not be resisted. I therefore quote again 

 from the work last cited, pp. 496-499. 



" Most male birds are highly pugnacious during the breeding season, and some possess weapons adapted for fight- 

 ing with their rivals. But the most pugnacious and the best armed males rarely or never depend for success solely upon 

 their power to drive away or kill their rivals, but have special means for charming the female. With some it is the power 

 of song, or of giving forth strange cries, or instrumental music, and the males in consequence ditfer in their vocal organs, 

 or in the structure of certain feathers. From the curiously diversified means for producing various sounds, we gain a 

 high idea of the importance of this means of courtship. Many birds endeavor to charm the female by love-dances or 

 antics, performed on the ground or in the air, and sometimes at prepared places. But ornaments of many kinds, the 

 most brilliant tints, combs, and wattles, beautiful plumes, elongated feathers, top-knots, and so forth, are by far the 

 commonest means. In some cases mere novelty appears to have acted as a charm. The ornaments of the males must be 

 highly important to them, for they have been acquired in not a few cases at the cost of increased danger from enemies, 

 and even at some loss of power in fighting with their rivals. The males of very many species do not assume their orna- 

 mental dress until they arrive at maturity, or they assume it only during the breeding season, or the tints then become 

 more vivid. Certain ornamental appendages become enlarged, turgid, and brightly colored during the act of courtship. 

 The males display their charms with elaborate care and to the best effect ; and this is done in the presence of the females. 

 The courtship is sometimes a prolonged affair, and many males and females congregate at an appointed place. To sup- 

 pose that the females do not appreciate the beauty of the males, is to admit that their splendid decorations, all their 

 pomp and display, are useless ; and this is incredible. Birds have fine powers of discrimination, and in some few cases 

 it can be shown that they have a taste for the beautiful. The females, moreover, are known occasionally to exhibit a 

 marked preference or antipathy for certain individual males. 



" If it be admitted that the females prefer, or are unconsciously excited by the more beautiful males, then the 

 males would slowly but surely be rendered more and more attractive through sexual selection. That it is this sex which 

 has been chiefly modified, we may infer from the fact that, in almost every genus where the sexes differ, the males differ 

 much more from one another than do the females ; this is well shown in certain closely-allied representative species, in 

 which the females can hardly be distinguished, whilst the males are quite distinct. Birds in a state of nature offer indi- 

 vidual differences which would amply sviffice for tlie work of sexual selection ; but we have seen that they occasionally 

 present more strongly-marked variations which recur so frequently that they would immediately be fixed, if they served 

 to allure the female. The laws of variation must determine the nature of the initial changes, and will have largely influ- 

 enced tlie final result. Tlie gradations, which may be observed between the males of allied species, indicate the nature 

 of the stejis througli whicli they have passed. They explain also in the most interesting manner how certain characters 

 have originated, such as the indented ocelli on the tail-feathers of the peacock and the ball and socket ocelli on the wing- 

 feathers of the Argus pheasant. It is evident that the brilliant colors, top-knots, fine plumes, &c., of many male birds 

 cannot have been acquired as a protection ; indeed, they sometimes lead to danger. That they are not due to the direct 

 and definite action of the conditions of life, we may feel assured, because the females have been exposed to the same con- 

 ditions, and yet often differ from the males to an extreme degree. Although it is probable that changed conditions act- 

 ing during a lengthened period liave in some cases produced a definite effect on both sexes, or sometimes on one sex 



