56 SEXUAL SELECTION : BIEDS. Part IL 



peacocks and drooping their wings.^^ It is also re- 

 markable tliat the birds which sing are rarely decorated 

 with brilliant colours or other ornaments. Of our British 

 birds, excepting the bullfinch and goldfinch, the best 

 songsters are j^lain-coloured. The king-fisher, bee-eater, 

 roller, hoopee, woodpeckers, &c., utter harsh cries ; and 

 the brilliant birds of the tropics are hardly ever song- 

 sters.^° Hence bright colours and the power of song- 

 seem to replace each other. We can perceive that if the 

 plumage did not vary in brightness, or if bright colours 

 were dangerous to the species, other means would liave 

 to be employed to charm the females ; and the voice 

 being rendered melodious would offer one such means. 



In some birds the vocal organs differ greatly in the 

 two sexes. In the Tetrao cujpido (fig. 39) the male has 

 two bare, orange- coloured sacks, one on each side of the 

 neck ; and these are largely inflated when the male, 

 during the breeding-season, makes a curious hollow 

 sound, audible at a great distance. Audubon proved 

 that the sound was intimately connected with this ap- 

 paratus, wliich reminds us of the air-sacks on each side 

 of the mouth of certain male frogs, for he found that 

 the sound was much diminished when one of the sacks 

 of a tame bird was pricked, and when both were pricked 

 it was altogether stopped. The female has "a some- 

 " w^hat similar, though smaller, naked space of skin on 

 " the neck ; but this is not capable of inflation. "^^ The 



39 Gould, 'Handbook to the Birds of Australia,' vol. i. 1865, p. 308- 

 :-;iO. See also Mr. T. W. Wood in the ' Student,' April, 1870, p. 125. 



^^ See remarks to this effect in Gould's ' Introduction to the Troclii- 

 lidge,' 1861, p. 22. 



^^ ' The Sportsman and Naturalist in Canada,' by IMajor W. Eoss 

 King, 1866, p. 144-146. Mr. T. ^Y . Wood gives in the ' Student ' 

 (April, 1870, p. 116) an excellent account of the attitude and habits <>f 

 this bird during its courtship. He states that the ear-tufts or neck- 

 plumes are erected, so that they meet over the crown of the head. 



