EVOLUTION OF THE COLORS OF BIRDS. 325 



Sexual selection appears to have been the chief factor 

 in the origination of the color markings of this genus. 

 The orange brown of the breast is an intensification of 

 yellow analogous to that of the crown of Helminthophila 

 celata. 



The young plumage shows the coloration of the primi- 

 tive bird dull olive and gray. 



GENUS DENDROICA. THE WOOD WARBLERS. 



(7) Adult male more conspicuously colored than 

 female; young similar to female, or (8) with a peculiar 

 first plumage; or, more rarely, (5) male differs from 

 female in breeding plumage only; young with peculiar 

 first plumage. 



Prevailing colors, black, white, olive green, yellow, 

 orange, bluish, chestnut. 



There seems to be little doubt that the varied color 

 markings of this extensive genus have been produced 

 for the most part by the action of sexual selection. As 

 this is a peculiarly favorable genus for the study of the 

 effects of sexual selection I have prepared tables of the 

 colors of the entire genus, one for the female or imma- 

 ture plumage and the other of the adult males (Plates 

 XVIII and XIX). In order to get the colors of any one 

 species read the colors in a line from right to left, while 

 to compare the colors of the same part of the body in 

 different species read the columns up and down. These 

 two tables illustrate sexual selection, pigment assort- 

 ment, environmental influences, and many less universal 

 points. It will be noticed that although the colors in 

 Plate XVIII are of dull monotonous tints, nearly all the 

 specialized colors are suggested. The general effect of this 

 plate is olive green on the left half and white or yellow 

 on the right. The only conspicuous exceptions to the 

 olive color are the three species in which the rump is 



