278 
DARWINISM 
CHAP. 
searching for some cause for this singular apparent exception 
to the rule of female protective colouring, I came upon a fact 
which beautifully explains it; for in all these cases, without 
exception, the species either nests in holes in the ground or in 
trees, or builds a domed or covered nest, so as completely to 
conceal the sitting - bird. We have here a case exactly 
parallel to that of the butterflies protected by distasteful- 
ness, whose females are either exactly like the males, or, if 
different, are equally conspicuous. We can hardly believe 
that so exact a parallel should exist between such remote 
classes of animals, except under the influence of a general 
law; and, in the need of protection by all defenceless animals, 
and especially by most female insects and birds, we have such 
a law, which has been proved to have influenced the colours 
of a considerable proportion of the animal kingdom . 1 
The general relation which exists between the mode of 
nesting and the coloration of the sexes in those groups of 
birds which need protection from enemies, may be thus 
expressed: When both sexes are brilliant or conspicuous, 
the nest is such as to conceal the sitting-bird; but when the 
male is brightly coloured and the female sits exposed on the 
nest, she is always less brilliant and generally of quite sober 
and protective hues. 
It must be understood that the mode of nesting has in¬ 
fluenced the colour, not that the colour has determined the 
mode of nesting ; and this, I believe, has been generally, though 
not perhaps universally, the case. For we know that colour 
varies more rapidly, and can be more easily modified and 
fixed by selection, than any other character; whereas habits, 
especially when connected with structure, and when they 
pervade a whole group, are much more persistent and more 
difficult to change, as shown by the habit of the dog turning 
round two or three times before lying down, believed to be 
that of the wild ancestral form which thus smoothed down 
the herbage so as to form a comfortable bed. We see, too, 
that the general mode of nesting is characteristic of whole 
families differing widely in size, form, and colours. Thus, all 
the kingfishers and their allies in every part of the world nest 
1 See the author's Contributions to Natural Selection, chap. vii., in which 
these facts were first brought forward. 
