60 SEXUAL SELECTION : BIRDS. Part IL 



more deej)ly embedded in the adult male than in the 

 female or young male. In the male Merganser the 

 enlarged portion of the trachea is furnished with an 

 additional pair of muscles^^ But the meaning of these 

 differences between the sexes of many Anatidae is not 

 at all understood ; for the male is not always the more 

 vociferous ; thus with the common duck, the male hisses, 

 whilst the female utters a loud quack.'"^ In both sexes of 

 one of the cranes (Grus virgo) the trachea penetrates 

 the sternum, but presents " certain sexual modifications." 

 In the male of the black stork there is also a w^ll- 

 marked sexual difference in the length and curvature of 

 the bronchi.^"^ So that highly important structures have 

 in these cases been modified according to sex. 



It is often difficult to conjecture whether the many 

 strauge cries and notes, uttered by male birds during 

 the breeding-season, serve as a charm or merely as a 

 call to the female. The soft cooing of the turtle-dove 

 and of many pigeons, it may be presumed, pleases the 

 female. When the female of the wild turkey utters her 

 call in the morning, the male answers by a different 

 note from the gobbling noise which he makes, when 

 with erected feathers, rustling wings and distended 

 Avattles, he puffs and struts before her.^^ The speZ of 

 the black-cock certainly serves as a call to the female, 

 for it has been known to bring four or five females 



•'^ Bishop, in Todd's ' Cyclop, of Anat. and Phys.' vol. iv. p. 1499. 



^^ The spoonbill (Platalea) has its trachea convoluted into a figure 

 of eight, and yet this bird (Jerdon, ' Birds of India,' vol. iii. p. 763) is 

 mute ; but Mr, Blyth informs me that the convolutions are not con- 

 stantly present, so that perhaps they are now tending towards abortion. 



•''■ ' Elements of Comp. Anat.' by R. Wagner, Eng. translat. 1845, p. 

 111. With respect to the swan, as given above, Yarrell's 'Hist, of 

 British Birds,' 2nd edit. 1845, vol. iii. p. 193. 



•*s C. L. Bonaparte, quoted in the ' Naturalist Library : Birds,' vol. 

 xiv. p. 126. 



