56 
SEXUAL SELECTION : BIRDS. 
Part IL 
peacocks and drooping tlieir wings.^^ It is also re- 
markable that 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 plain-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 have 
to be employed to charm the females ; and the voice 
beino' rendered melodious would offer one such means. 
o 
In some birds the vocal organs differ greatly in the 
two sexes. In the Tetrao eujpido (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, which 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- 
what similar, though smaller, naked space of skin on 
the neck; but this is not capable of inflation, The 
Gould, ‘ Handbook to the Birds of Australia,’ vol. i. 1865, p. 308- 
310. See also Mr. T. W. Wood in the ‘ Student,’ April, 1870, p. 125. 
See remarks to this effect in Gould’s ‘ Introduction to the Trochi- 
lidse,’ 1861, p. 22. 
' The Sportsman and Naturalist in Canada,’ by Major W. Ross 
King, 1866, p. 144-146. Mr. T. W. Wood gives in the ‘ Student ’ 
(April, 1870, p. 116) an excellent account of the attitude and habits of 
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. 
