90 GENERAL ORNITHOLOGY. 



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

 adult females.^' — (Darwin, Desc. of Man, new ed., 1881, p. 466.) 



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

 conclusion of the whole matter in Dai'win's own words, summary of his views of Sexual 

 Selection 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 somepoBseas weapons adapted for 

 fighting 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 

 differ in their vocal organs, or in the structure of certain feathers. From the curiously diversified means for pro- 

 ducing 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 ornamental 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 pro- 

 longed afTair, and many males and females congregate at an appointed place. To suppose 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 shewn 

 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 

 tliis 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, whil^tr the males are quite distinct. Birds 

 in a state of nature offer individual differences which would amply suffice for the 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 influenced the final result. The gradations, which may be observed 

 between the males of allied species, indicate the nature of the steps through which 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 lifie, we may feel assured, because the females have been exposed to the same conditions, 

 and yet often differ from the males to an extreme degree. Although it is probable that changed conditions acting 

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

 alone, the more important result will have been an increased tendency to vary or to present more strongly marked 

 individual differences : and" such differences will have afforded an excellent ground-work for the action of sexua) 

 selection. 



"The laws of inheritance, irrespectively of selection, appear to have determined whether the characters 

 acquired by the males for the sake of ornament, for producing various sounds, and for fighting together, have been 

 transmitted to the males alone or to both sexes, either permanently, or periodically during certain seasons of the 

 year. Why various characters should have been transmitted sometimes in one way and sometimes in another, is not 

 in most cases known ; but the period of variability seems often to have been the determining cause. When the 

 two sexes have Inherited all characters in common, they necessarily resemble each other; but as the successive 

 variations may be differently transmitted, every possible' gradation may be fbund, even within the same genus, 

 from the closest similarity to the widest dissimilarity between the sexes. With many closely-allied species, follow- 

 ing nearly the same habits of life, the males have come to differ from each other chiefly through the action of 

 sexual selection; whilst the females have come to differ chiefly from partaking more or less of the characters thus 

 acquired by the males. The effects, moreover, of the definite action of the conditions of life, will not have been 

 masked in the females, as in the males, by the accumulation through sexual selection of strongly-pronounced colors 

 and other ornaments. The individuals of both sexes, however affected, will have been kept at each successive 

 period nearly uniform by the free intercrossing of many individuals. 



" With species, in which the sexes differ In color, it is possible or probable that some of the successive varia- 

 tions often tended to be transmitted equally to both sexes; but that when this occurred the females were pre- 



