BIRDS. 563 



rendered pure white and thus made conspicuous to their 

 enemies; or that the adults of one of these two species 

 should have been specially rendered white during the 

 winter in a country which is never covered with snow. On 

 the other hand, we have good reason to believe that white- 

 ness has been gained by many birds as a sexual ornament. 

 We may therefore conclude that some early progenitor of. 

 the Ardea asha and the Buphus acquired a white plumage 

 for nuptial purposes, and transmitted this color to their 

 young; so that the young and the old became white like 

 certain existing egrets; and that the whiteness was after- 

 ward retained by the young, while it was exchanged by the 

 adults for more strongly pronounced tints. But if we 

 could look still further back to the still earlier progenitors 

 of these two species we should probably see the adults dark- 

 colored. I infer that this would be the case from the 

 analogy of many other birds which are dark while young 

 and when adult are white; and more especially from the 

 case of the Ardea gularis, the colors of which are the 

 reverse of those of A. asha, for the young are dark-colored 

 and the adults white, the young having retained a forme? 

 state of plumage. It appears therefore that during a lonj 

 line of descent, the adult progenitors of the Ardea aslia> 

 the Buphus, and of some allies, have undergone the follow- 

 ing changes of color: fiistly, a dark shade; secondly, pure 

 white, and thirdly, owing to another change of fashion (if 

 I may so express myself), their present slaty, reddish, or 

 golden-buff tints. 'These successive changes are intelligi- 

 ble only on the principle of novelty having been admired 

 by birds for its own sake. 



Several writers have objected to the whole theory of 

 sexual selection by assuming that with animals and savages 

 the taste of the female for certain colors or other ornaments 

 would not remain constant for many generations; that first 

 one color and then another would be admired, and conse- 

 quently that no permanent effect could be produced. We 

 may admit that taste is fluctuating, but it is not quite arbi- 

 trary. It depends much on habit, as we see in mankind ; 

 and we may infer that this would hold good with birds and 



with, their specific names. Audubon (" Ornith. Biography," vol. iii, 

 p. 416; vol. iv, p. 58) seems rather pleased at the thought that this 

 remarkable change of plumage will greatly "disconcert the system- 

 atists." 



