608 THE DESCENT OF MAN 



female. The male pintail-duck {Anas acuta) loses his plu- 

 mage for the shorter period of six weeks or two months; and 

 Montagu remarks that "this double moult within so short a 

 time is a most extraordinary circumstance, that seems to bid 

 defiance to all human reasoning. ' ' But the believer in the 

 gradual modification of species will be far from feeling sur- 

 prise at finding gradations of all kinds. If the male pintail 

 were to acquire his new plumage within a still shorter period, 

 the new male feathers would almost necessarily be mingled 

 with the old, and both with some proper to the female ; and 

 this apparently is the case with the male of a not distantly 

 allied bird, namely the Merganser serrator, for the males are 

 said to "undergo a change of plumage, which assimilates 

 them in some measure to the female. ' ' By a little further 

 acceleration in the process, the double moult would be com- 

 pletely lost."' 



Some male birds, as before stated, become more brightly 

 colored in the spring, not by a vernal mount, but either by 

 an actual change of color in the feathers or by their ob- 

 scurely colored deciduary margins being shed. Changes 

 of color thus caused may last for a longer or shorter time. 

 In the Pelecanus onocrotalus a beautiful rosy tint, with 

 lemon-colored marks on the breast, overspreads the whole 

 plumage in the spring; but these tints, as Mr. Sclater states, 

 "do not last long, disappearing generally in about six weeks 

 or two jmonths after they have been attained. ' ' Certain finches 

 shed the margins of their feathers in the spring, and then be- 

 come brighter colored, while other finches undergo no such 

 change. Thus the Fringilla tristis of the United States (as 

 well as many other American species) exhibits its bright 

 colors only when the winter is past, while our goldfinch, 

 which exactly represents this bird in habits, and our siskin, 

 which represents it still more closely in structure, undergo 

 no such annual change. But a difference of this kind ia 



^ See Macgillivray, "Hist. British Birds" (vol. v. pp. 34, tO and 223), 

 on the luoQlting of the Anatidae, with quotations from Watertoa and Montagu. 

 Ako Yarrell, "Hist, of British Birds," voL iii. p. 243. 



