588 THE DESCENT OF MAN 



United States," will feel any great difficulty in admitting 

 that birds, either by a change (in the strict sense of the 

 word) of their habits, or through the natural selection of 

 so-called spontaneous variations of instinct, might readily 

 be led to modify their manner of nesting. 



This way of viewing the relation, as far as it holds good, 

 between the bright colors of female birds and their manner 

 of nesting, receives some support from certain cases occur- 

 ring in the Sahara Desert. Here, as in most other deserts, 

 various birds and many other animals have had their colors 

 adapted in a wonderful manner to the tints of the surround- 

 ing surface. Nevertheless there are, as I am informed by 

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

 thus the male of the Monticola cyanea is conspicuous from 

 his bright blue color, and the female almost equally con- 

 spicuous from her mottled brown and white plumage; both 

 sexes of two species of Dromolsea are of a lustrous black; 

 so that these three species are far from receiving protection 

 from their colors, yet they are able to survive, for they have 

 acquired the habit of taking refuge from danger in holes 

 or crevices in the rocks. 



With respect to the above groups in which the females 

 are conspicuously colored 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 afterward transmitted this instinct, 

 together with their bright Colors, to their modified descend- 

 ants. As far as it can be trusted, the conclusion is inter- 

 esting, that sexual selection, together with equal or nearly 

 equal inheritance by both sexes, have indirectly determined 

 the manner of nidification of whole groups of birds. 



According to Mr. "Wallace, even in the groups in which 

 the females, from being protected in domed nests during in- 



'^ See many slatements in the "Ornithological Biography." See, also, 

 some curious observations on the nests of Italian birds by Eugenic Bettoni, 

 in the "Atti della Society Italiana," vol. xi., 1869, p. 481. 



