226 
SEXUAL SELECTION: BIEDS. 
Part II. 
mented with bright tints. It would appear that female 
birds, as a general rule, have selected their mates 
either for their sweet voices or gay colours, but not 
for both charms combined. Some species which are 
manifestly coloured for the sake of protection, such 
as the jack-snipe, woodcock, and night-jar, are like- 
wise marked and shaded, according to our standard 
of taste, with extreme elegance. In such cases we 
may conclude that both natural and sexual selection 
have acted conjointly for protection and ornament. 
Whether any bird exists which does not possess some 
special attraction, by which to charm the opposite sex, 
may be doubted. When both sexes are so obscurely 
coloured, that it would be rash to assume the agency 
of sexual selection, and when no direct evidence can 
be advanced shewing that such colours serve as a pro- 
tection, it is best to own complete ignorance of the 
cause, or, which comes to nearly the same thing, to 
attribute the result to the direct action of the con- 
ditions of life. 
There are many birds both sexes of which are con- 
spicuously, though not brilliantly coloured, such as 
the numerous black, white, or piebald species ; and 
these colours, are probably the result of sexual selec- 
tion. With the common blackbird, capercailzie, black- 
cock, black Scoter-duck (Oidemia), aud even with one 
of the Birds of Paradise {Lophorina atra), the males 
alone are black, whilst the females are brown or mot- 
tled ; and there can hardly be a doubt that blackness 
in these cases has been a sexually selected character. 
Therefore it is in some degree probable that the com- 
plete or partial blackness of both sexes in such birds 
as crows, certain cockatoos, storks, and swans, and many 
marine birds, is likewise the result of sexual selec- 
tion, accompanied by equal transmission to both sexes ; 
