EVOLUTION OF THE COLORS OF BIRDS. 301 



As the male is uniformly more brightly colored and 

 has more special markings than the female, the colora- 

 tion has undoubtedly been acquired by sexual selection 

 in accordance with the law of the assortment of pig- 

 ments. Reference has already been made to the sup- 

 position that this golden color which was acquired for 

 adornment may have been utilized for protection since 

 the CompositiTe to which they so commonly resort are 

 colored thus (see ante, p. 195). The pine finch (8. piaus) 

 retains a plumage but little modified from the bird which 

 was the common ancestor of the entire group. 



Genus Plectrophenax. The Snowflakes. 



(6) Plumage of male and female changes with the 

 season; male unlike female in both plumages; young 

 similar to female, but duller and more streaked. 



Prevailing colors, white, black, gray, brown, buffy. 



There is a strong tendency in this genus towards the 

 assumption of a completely white plumage. The ances- 

 tral form was a streaked bird, as shown by the present 

 condition of the young. Next a black and white plumage 

 was assumed, which still persists to a certain degree, 

 although the black is becoming eliminated. Thus Mr. 

 E. W. Nelson writes as follows concerning an abnormal 

 P. nivalis:"^ " One specimen, a female, obtained at Saint 

 Michaels, April, 1879, is pure white over the entire 

 body, with the exception only of the tips of the prim- 

 aries for an inch from their ends. This part of the 

 primaries is jet black, mainly on the inner web, with a 

 narrow edge of white at the tip, but the shaft and most 

 of the outer web are white. The tail is pure white with- 

 out a trace of black. The bases of the feathers are not 

 black, as is usually the case with this bird, but are dark 



* Eeport upon Natural History Collections made iu Alaska. Arctic 

 Series of Pnb. Issued in Connection with Sig. Service, U. S. Army, p. 182. 



