vi A THEORY OF BIRDS' NESTS 135 



formed chiefly of fir-twigs and lichens. Now the delicate 

 gray and ashy and purplish hues of the head and back, to- 

 gether with the yellow of the wings and tail, are tints that 

 exactly harmonise with the colours of fir leaves, bark, and 

 lichens, while the brilliant red wax tips exactly represent the 

 crimson fructification of the common lichen, Cladonia cocci- 

 fera. When sitting on its nest, therefore, the female bird 

 will exhibit no colours that are not common to the materials 

 by which it is surrounded ; and the several tints are distri- 

 buted in about the same proportions as they occur in nature. 

 At a short distance the bird would be undistinguishable from 

 the nest it is sitting on, or from a natural clump of lichens, 

 and will thus be completely protected. 



I think I have now noticed all exceptions of any import- 

 ance to the law of dependence of sexual colour on modification. 

 It will be seen that they are very few in number, compared 

 with those which support the generalisation ; and in several 

 cases there are circumstances in the habits or structure of the 

 species that sufficiently explain them. It is remarkable also 

 that I have found scarcely any positive exceptions that is, 

 cases of very brilliant or conspicuous female birds in which 

 the nest was not concealed. Much less can there be shown 

 any group of birds in which the females are all of decidedly 

 conspicuous colours on the upper surface, and yet sit in open 

 nests. The many cases in which birds of dull colours in both 

 sexes make domed or concealed nests do not, of course, affect 

 this theory one way or the other ; since its purpose is only 

 to account for the fact that brilliant females of brilliant 

 males are always found to have covered or hidden nests, while 

 obscure females of brilliant males almost always have open and 

 exposed nests. The fact that all classes of nests occur with 

 birds which are dull coloured in both sexes merely shows 

 that these dull colours serve to protect the parents at other 

 times than when sitting on the nest, the structure of which is 

 determined by the requirements of the offspring. 



If the views here advocated are correct, as to the various 

 influences that have determined the specialities of every bird's 

 nest, and the general coloration of female birds, with their 

 action and reaction on each other, we can hardly expect to 

 find evidence more complete than that here set forth. Nature 



