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. 



