BIRDS. 407 



CHAPTER Xm. 



SECOifDARY SEXUAL CHARACTEBS OF BIRDS. 



Sexual differences Law of battle Special weapons Vocal organs 

 Instrumental music Love-antics and dances Decorations, 

 permanent 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, 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 sacks, top-knots, naked 

 shafts, plumes and lengthened feathers gracefully spring- 

 ing from all parts of the body. The beak and naked skin 

 about the head and the feathers are often gorgeously col- 

 ored. 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. Ramsay,* 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-season that it can 

 be detected long before the bird can be seen.f On the 

 whole, birds appear to be the most aesthetic of all animals, 

 excepting of course man, and they have nearly tlie same 



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



f Gould, *' Hand-book to the Birds of Australia," 1865, vol. ii, p. 

 383. 



