172 SEXUAL SELECTION : BTEDS. Part IL 



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- 

 derful manner to the tints of the surrounding surface. 

 Nevertheless there are, as I am informed bv the Rev. 

 Mr. Tristram, some curious exceptions to the rule ; thus 

 the male of the Monticola cyanea is conspicuous from 

 his bright blue colour, and the female almost equally 

 conspicuous from her mottled brown and white plumage; 

 both sexes of t^^ o species of Dromolsea 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 

 buikl 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- 

 fied 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 coEsiderable degree, from 



