The vocal organs of various web-footed and wading birds are
extraordinarily complex, and differ to a certain extent in the two
sexes. In some cases the trachea is convoluted, like a French horn, and
is deeply embedded in the sternum. In the wild swan (Cygnus ferus) it
is more deeply embedded in the adult male than in the adult female or
young male. In the male Merganser the enlarged portion of the trachea
is furnished with an additional pair of muscles. (45. Bishop, in Todd s
Cyclopaedia of Anatomy and Physiology, vol. iv. p. 1499.) In one of
the ducks, however, namely Anas punctata, the bony enlargement is only
a little more developed in the male than in the female. (46. Prof.
Newton, Proc. Zoolog. Soc. 1871, p. 651.) But the meaning of these
differences in the trachea of the two sexes of the Anatidae is not
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. (47. 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
constantly present, so that perhaps they are now tending towards
abortion.) 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 well-marked sexual
difference in the length and curvature of the bronchi. (48. Elements
of Comparative Anatomy, by R. Wagner, Eng. translat. 1845, p. 111.
With respect to the swan, as given above, Yarrell s History of British
Birds, 2nd edition, 1845, vol. iii. p. 193.) Highly important
structures have, therefore, 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 note which differs from the gobbling noise made, when with
erected feathers, rustling wings and distended wattles, he puffs and
struts before her. (49. C.L. Bonaparte, quoted in the Naturalist
Library: Birds, vol. xiv. p. 126.) The spel of the black-cock
certainly serves as a call to the female, for it has been known to
bring four or five females from a distance to a male under confinement;
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