36 SEXUAL SELECTION. [Pakt II. 



CHAPTER XIII. 



Secondary Sexual Characters of Birds. 



Sexual Differences. — Law of Battle. — Special "Weapons.— Vocal Organs. — 

 Instrumental Music. — Love- Antics and L>ances.— Decorations, Perma- 

 nent and Seasonal. — Double and Single Annual Moults. — Display of 

 Ornaments by the Males. 



Secondary 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 consider- 

 able length. Male birds sometimes, though rarely, pos- 

 sess special weapons for fighting with each other. They 

 charm the females 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 observ- 

 sr, Mr. Ramsay, 1 says of the Australian musk-duck (Bizi- 

 ura lobata) 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 



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



