128 
NATURAL SELECTION 
vi 
In the extensive families of the warblers (Sylviadse), 
thrushes (Turdidse), flycatchers (Muscicapidee), and shrikes 
(Laniadse), a considerable proportion of the species are beauti- 
fully marked with gay and conspicuous tints, but in every 
case the females are less gay, and are most frequently of the 
very plainest and least conspicuous hues. Now, throughout 
the whole of these families the nest is open, and I am not aware of 
a single instance in which any one of these birds builds a 
domed nest, or places it in a hole of a tree, or under ground, or in 
any place where it is effectually concealed. 
In considering the question we are now investigating, it is 
not necessary to take into account the larger and more power- 
ful birds, because they seldom depend much on concealment 
to Secure their safety. In the raptorial birds bright colours 
are as a rule absent ; and their structure and habits are such 
as not to require any special protection for the female. The 
larger waders are sometimes very brightly coloured in both 
sexes; but they are probably little subject to the attacks of 
enemies, since the scarlet ibis, the most conspicuous of birds, 
exist in immense quantities in South America. In game birds 
and water-fowl, however, the females are often very plainly 
coloured, when the males are adorned with brilliant hues ; 
and the abnormal family of the Megapodidse offers us the in- 
teresting fact of an identity in the colours of the sexes (which 
in Megacephalon and Talegalla are somewhat conspicuous), in 
conjunction with the habit of not sitting on the eggs at all. 
What the Facts Teach us 
Taking the whole body of evidence here brought forward, 
embracing as it does almost every group of bright-coloured 
birds, it will, I think, be admitted that the relation between 
the two series of facts in the colouring and nidification of 
birds has been sufficiently established. There are, it is true, 
a few apparent and some real exceptions, which I shall con- 
sider presently ; but they are too few and unimportant to 
weigh much against the mass of evidence on the other side, 
and may for the present be neglected. Let us then consider 
what we are to do with this unexpected set of correspondences 
between groups of phenomena which, at first sight, appear so 
disconnected. Do they fall in with any other groups of 
