316 THE STRUCTURE AND LIFE OF BIRDS CHAP. 
she sits upon the nest. We might expect, then, that 
she would be more soberly coloured than her partner. 
And this is what we do find, with the remarkable 
exception which so admirably supports Dr. Wallace’s 
theory, that among birds which nest in holes, so that 
the hen as she sits is concealed, the bright colours 
are very frequently common to both sexes. This is 
the case eg. with the Kingfisher. The hen Wood- 
pecker is brilliantly coloured, though less so than the 
cock. The conspicuously-coloured Pigeons sit exposed 
upon the nest; but Natural Selection only requires 
that a species should have some means of maintaining 
itself. The particular means which we find in opera- 
tion is due to unknown causes. Thus the Pigeon’s 
great power of flight, and the ease with which he finds 
food, may render protective coloration unnecessary 
to him. 
There is good reason, then, why in most cases the 
hen should be dull-coloured. But this affords no 
explanation of the enormous plumes of the Peacock, 
the Argus Pheasant, the Lyre Bird, and the Bird of 
Paradise. a 
Dr. Wallace’s views on this subject I will give 
in his own words: “ The fact that they (long plumes) 
have been developed to such an extent in a few 
species is an ‘indication of such perfect adaptation to 
the conditions of existence, such complete success in 
the battle for life, that there is in the adult male, at 
all events, a surplus of strength, vitality, and growth 
power which is able to expend itself in this way with- 
out injury.”* This is very strange as coming from the 
1 aa 
Darwinism, p. 293. 
