60 
SEXUAL SELECTION : BIRDS. 
Part II. 
more deeply 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 AnatidaB 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 virgfo) the trachea penetrates 
the sternum, but presents certain sexual modifications.’’ 
In the male of the black stork there is also a well- 
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 
strange 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 wffiich he makes, when 
with erected feathers, rustling wings and distended 
wattles, he puffs and struts before her.^^ The spel of 
the black-cock certainly serves as a call to the female, 
for it has been knowm to bring four or five females 
Bishop, in Todd’s ‘ Cyclop, of Anat. and Pliys.’ 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. 
^7 ‘ Elements of Comp. Anat.’ by R. V^agner, 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. 
C. L. Bonaparte, quoted in the ‘ Naturalist Library : Birds,’ vol. 
xiv. p. 126. 
