EVOLUTION OF THE COLORS OF BIRDS. 145 



view which seems to be more in harmony with the facts. 

 Brown and gray are generally present in species in 

 which the markings are not highly specialized. More- 

 over, these colors very frequently occur in the young of 

 species which are highly specialized in the adult, as, for 

 example, in the red-headed woodpecker (Meianerpes 

 erythrocephalus) . The presence of brown or gray in al- 

 most every genus of North American birds, either in the 

 young or the adult stage, would seem to indicate that 

 these are the most primitive colors, and that where they 

 still occur it is due to a lack of specialization in this 

 respect. To be sure, in many cases this specialization 

 may be retarded in many instances by the positive ad- 

 vantage of protection, or protection on the contrary 

 may enable it to continue. As an excellent example of 

 these two cases may be mentioned the goldfinches. The 

 pine finch (Spinus pinus), retains the primitive plum- 

 age, perhaps from the need of protection, while the gold- 

 finches (Spinus tristis for example), have become special- 

 ized in color without sacrificing protection. They 

 frequent during the summer the yellow composite, in 

 the vicinity of which they can be detected only with 

 great difficulty. 



This view would be in harmony with the law of assort- 

 ment of pigments. The tendency would be to progress 

 from such mixed shades as brown and gray to the pure 

 colors. The need of recognition would in any event be 

 sufficient to account for the early and universal tend- 

 ency to produce limited areas of black and white. It 

 might at first sight appear as if the fact that green is 

 less frequently found than either of its constituent ele- 

 ments, yellow and blue, would militate against the law 

 of the assortment of pigments. This discrepancy is only 

 an apparent one, however. The green pigment of the 

 bird is a different chemical substance from either the 

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