466 THE DESCENT OF MAN 



CHAPTER XIII 



SEOONDAET SEXUAL CHARACTERS OF BIRDS 



Sexual diffierences — Law of battle — Special weapons — Vocal organa — 

 Instrumental music — Love-antics and dances — Decorations, perma- 

 nent and seasonal — Double and single annual moults — Display of 

 ornaments by the males 



SECOND AEY sexual characters are more diversified 

 and conspicuous in birds, though not perhaps entail- 

 ing more important changes of structure, than in any 

 other class of animals. I shall, therefore, treat the subject at 

 considerable length. Male birds sometimes, though rarely, 

 possess special weapons for fighting with each other. They 

 charm the female by vocal or instrumental music of the 

 most varied kinds. They are ornamented by all sorts of 

 combs, wattles, protuberances, horns, air-distended sacs, 

 topknots, naked shafts, plumes and lengthened feathers 

 gracefully springing from all parts of the body. The beak 

 and naked skin about the head, and the feathers, are often 

 gorgeously colored. The males sometimes pay their court 

 by dancing, or by fantastic antics performed either on the 

 ground or in the air. In one instance, at least, the male 

 emits a musky odor, which we may suppose serves to charm 

 or excite the female ; for that excellent observer, Mr. Ram- 

 say,' says of the Australian musk-duck {Biziura lohata) 

 that "the smell which the male emits during the summer 

 months is confined to that sex, and in some individuals is 

 retained throughout the year; I have never, even in the 

 breeding season, shot a female which had any smell of 

 musk." So powerful is this odor during the pairing sea- 

 son, that it can be detected long before the bird can be 



' "Ibis," vol. lii. (new series), 1867, p. 414. 



