BIHDS. 519 



their instincts (supposing that they originally built open 

 nests) and to seek protection by building domed or con- 

 cealed nests. No one who studies,, for instance, Audubon's 

 account of the differences in the nests of the same species 

 in the Northern and Southern 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 Rev. 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 

 descendants. As far as it can be trusted the conclusion is 

 interesting, 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 



* See many statements in the "Ornithological Biography." See 

 also some curious observations on the nests of Italian birds by 

 Eugenio Bettoni, in the " Atti deila Societa Italiana," vol. xi, 1869, 

 p. 487. 



