EVOLUTION OF THE COLORS OF BIRDS. 219 



The above list stands midway between those species 

 in which the adult female is like the adult male, and 

 such as differ in the adult plumage. It includes such 

 forms as vary with the seasons in which the male may 

 or may not be different from the female in summer, but 

 is not markedly so in winter. This division of forms 

 displaying seasonal differences is perhaps the least mod- 

 ified type of sexual adornment, for the male simply puts 

 on his courting garb for a brief season, when it is 

 obviously assumed to attract the attention and admira- 

 tion of the female. 



(3.) In the water-ouzel (Cinclus mexicanus) the sexes 

 are alike, but in winter the breast is much suffused with 

 white. The young plumage is like that of the adult in 

 winter. In this class the colors are obviously not sexual, 

 but the more primitive plumage appears during the 

 winter months. The increased vigor during the breed- 

 ing season has produced acceleration in the develop- 

 ment of pigment at that time of the year. 



(4.) As an example of this class may be mentioned 

 the palm warbler ( Dendroica pahnarum), in which species 

 the sexes are alike, the colors becoming broken and 

 obscured in the winter plumage. The young are a 

 plain dusky, streaked above and below. 



(5.) In Audubon's warbler (Dendroica aitduboni), the 

 y^Uow-rumped warbler (D. coronata), and the magnolia 

 warbler fZ). maculosa) the plumage of the male in sum- 

 mer is similar to that of the female, but all the markings 

 greatly accentuated and intensified. In winter the sexes 

 are very much alike, while the plumage of the young 

 is considerably less specialized than that of the female. 



The changes in plumage of the crossbills (Loxia) is 

 especially complex, for the male frequently passes 

 through three phases of plumage — first a gray phase, 

 then yellow, and finally red. In general, it may be said 



