172 
SEXUAL selection: birds. 
Part II. 
This way of viewing the relation, as far as it holds 
good, between the bright colours of female birds and 
their manner of nesting, receives some support from 
certain analogous cases occurring in the Sahara Desert. 
Here, as in most other deserts, various birds, and many 
other animals, have had their colours adapted in a won- 
<ierful manner to the tints of the surrounding surface. 
Nevertheless there are, as I am informed by the Eev. 
Mr. Tristram, some curious exceptions to the rule ; thus 
the male of the Montieola cyanea is conspicuous from 
his bright blue colour, and the female almost equally 
conspicuous from her mottled brown and white plumage ; 
both sexes of two species of Dromolaea are of a lustrous 
black ; so that these three birds are far from receiving 
protection from their colours, yet they are able to sur- 
vive, for they have acquired the habit, when in danger, 
of taking refuge in holes or crevices in the rocks. 
With respect to the above-specified groups of birds, 
in which the females are conspicuously coloured and 
build concealed nests, it is not necessary to suppose 
that each separate species had its nidifying instinct 
specially modified ; but only that the early progenitors 
of each group were gradually led to build domed or 
concealed nests ; and afterwards transmitted this in- 
stinct, together with their bright colours, to their modi- 
£ed descendants. This conclusion, as far as it can be 
trusted, is interesting, namely, that sexual selection, 
together with equal or nearly equal inheritance by both 
sexes, have indirectly determined the manner of nidifi- 
' cation of whole groups of birds. 
Even in the groups in which, according to Mr. Wal- 
lace, the females from being protected during nidifica- 
tion, have not had their bright colours eliminated 
through natural selection, the males often differ in a 
slight, and occasionally in a considerable degree, from 
