176 
SEXUAL SELECTION: BIRDS. 
pA 
jK' 
plumage between the sexes are of the 
nature as the occasionally greater differences. - . 
illustration of this fact has already been afford 131 
same 
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those kingfishers in which either the tail a!t "'> 
in 
aloo* 
the whole upper surface of the plumage differs >- |, 
same manner in the two sexes. Simiiar cases i )ill ',i!i 
observed with parrots and pigeons 
The differ 00 ^ 
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colour between the sexes of the same species are ^pii! 
of the same general nature as the differences i u 
between the distinct species of the same group 
VX UiiV CUIlUVy rj 
when in a group in which the sexes are usually 
the male differs considerably from the female, A 
not coloured in a quite new style. Hence 
infer that within the same group the special coIo u 'V 
of 
both sexes when they are alike, and the colours 
male, when he differs slightly or even consider»H v ' 
the female, have in most cases been determined ^ 
abW*’ 
same general cause ; this being sexual selection- 
It is not probable, as has already been 
.. w*-' x»x»o WHOMLiy UCWU - 
that differences in colour between the sexes, whe* 
jj-i ivimu PJCtutCll tilt? (SCACoj rr 
slight, can be of service to the female as a p r ° te< jj ! vli l 
Assuming, however, that they are of service, they Jll , p0 
A.1 Lx X , - . ... ... , 
be thought to he cases of transition; but we 
- - » — tin 
reason to believe that many species at any 0,) ' 
are undergoing 
change. 
Therefore we can 
it<; 
<6 
admit that the numerous females which di$ e * ^ 
slightly in colour from their males are now ; d 
meucing to become obscure for the sake of p 1 ' 0 ^ $ 
Lven it we consider somewhat more marked seS ! l ' () ('tl |1 ' 
- 1 * ,,v wxioiu«i- Bwmewnai more manceu 
ferermes, is it probable, for instance, that the bea 1 ^ 
female chaffinch, the crimson on the breast of tb e jb 
bullfinch,— the green of the female greenfincjO 
“ ' ’ »n • ' 
¥ 
crest of the female golden-crested wren, have - . ^ ,» 
rendered less bright by the slow process of sele ct !‘- 
the sake of protection ? I cannot think so ; and 
