BIRDS 157 



would result in proving that there are special conditions 

 influencing the development and structure of the feathers in 

 the two sexes, giving rise in the one case to green, in the 

 other to blue and red. There is no evidence, so far as I 

 know, that sexual selection has anything to do with the 

 matter. 



Anseres. The wild drake, Anas boschas, pairs with a 

 single female, and nevertheless has marked unisexual char- 

 acters in his plumage. The green speculum on the wings is 

 common to both sexes, though duller and somewhat smaller 

 in the female, and is developed early in life, whilst the 

 curled tail feathers and other ornaments are confined to the 

 male, and are developed later. As in other cases, the drake 

 loses his special plumage after the breeding season. He 

 remains without it for three months, during which period he 

 resembles the female. 1 



In Anas acuta, the Pintail Duck, the male loses his special 

 plumage for only about six weeks or two months. 



I do not know whether any special movements of the tail 

 feathers are performed by the wild drake in courtship, but 

 I think it is probable that some special stimulation of the 

 papillae of these feathers may take place, and may be the 

 cause of their peculiar shape. The fact of the difference 

 between the feathers, chiefly in colour, after the moult and 

 those of the breeding plumage in the drake, suggests strongly 

 that the action of the nervous system under the influence of 

 sexual excitement has something to do with the brilliant 

 colours of the breeding plumage. The special plumage of 

 the male, as in so many others cases, is only developed at 

 maturity, and the close correspondence of special brilliant 

 coloration with sexual excitement is certainly, in my 

 opinion, not without significance. This is one of the cases 

 in which the conditions of life other than sexual excitement 



1 Macgillivray, Hist. British Birds, vol. v. 



