4.94 The Descent of Man. Part IT. 



parts of a purer white, and the variously coloured daik parts of 

 still darker tints than the female. 



It would even appear that mere novelty, or slight changes for 

 the sake of change, have sometimes acted on female birds as a 

 charm, like changes of fashion with us. Thus the males of 

 some parrots can hardly be said to be more beautiful than the 

 females, at least according to our taste, but they differ in such 

 points, as in having a rose-coloured collar instead of " a bright 

 " emeraldine narrow green collar;" or in the male having a black 

 collar instead of " a yellow demi-collar in front," with a pale 

 roseate instead of a plum-blue head. 55 As so many male birds 

 have elongated tail-feathers or elongated crests for their chief 

 ornameni, the shortened tail, formerly described in the male of 

 a humming-bird, aud the shortened crest of the male goosander, 

 seem like one of the many changes of fashion which we admire 

 in our own dresses. 



Some members of the heron family offer a still more curious 

 case of novelty in colouring having, as it appears, been appre- 

 ciated for the sake of novelty. The young of the Ardea asha are 

 white, the adults being dark slate coloured ; and not only the 

 young, but the adults in their winter plumage, of the allied 

 Buphus coromandus are white, this colour changing into a 

 rich golden-buff during the breeding-season. It is incredible 

 that the young of these two species, as well as of some other 

 members of the same family, 55 should for any special purpose, 

 have been 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 whiteness 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 colour to their young ; so that the young and the old 

 became white like certain existing egrets ; and that the whiteness 

 was afterwards retained by the young, whilst 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- 



55 



See Jerdon on the genus specific namss. Audubon (' Ornith. 



Paloeornis, 'Birds of India,' vol. i. Biography,' vol. iii. p. 416 ; vol. iv. 



p. 258-260. p. 58) seems rather pleased at the 



56 The young of Ardea ?mfcscens thought that this remarkable change 



and A. coerulea of the U. States are of plumage will greatly "disconceil 



likewise white, the adults being " the systematists." 

 noloured in accordance with their 



