38 SEXUAL SELECTION. Part II. 



CHAPTER XIII. 



Secondary Sexual Characters of Birds. 



Sexual differences — Law of battle — Special weapons — Vocal 

 orfrans — Instrumental music — Love - antics and dances — 

 Decorations, permanent and seasonal — Double and single 

 annual moults — Display of ornaments by the males. 



iSecondaky sexual characters are more diversified and 

 conspicuous in birds, though not perhaps entailing more 

 important changes of structure, than in any other class 

 of animals. I shall, therefore, treat the subject at con- 

 siderable length. Male birds sometimes, though rarely, 

 possess special weapons for fighting with each other. 

 They charm the females by vocal or instrumental music 

 of the most varied kinds. Tliey 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 coloured. The 

 males sometimes pay their court by dancing, or by fan- 

 tastic antics performed either on the ground or in the air. 

 In one instance, at least, the male emits a musky odour 

 which we may suppose serves to charm or excite the 

 female ; for that excellent observer, Mr. Eamsay,^ says 

 of the Australian musk-duck {Biziura lobata) that " the 

 " smell which the male emits during the summer 

 " months is confined to that sex, and in some indi- 

 '' viduals is retained throughout the year ; I have never 



* 'Ibis,' vol. iii. (new series) 1867, p. 414. 



