EVOLUTION OF THE COLOES OF BIRDS. 155 



a more primitive stage of development than the red. 

 For instance, in the family Icteridse we have the red 

 winged blackbirds (Agelaius) with a scarlet shoulder 

 patch. In the same family is the yellow-headed black- 

 bird ( Xanthocephalus xanthocephcdus) . This fact in itself 

 would be of little significance, but may be explained in 

 accordance with the law of assortment of pigments 

 together with the correlation between red and yellow. 

 Of far more significance are the colors in the grosbeaks 

 (Hahia). In the male rose-breasted grosbeak (H. ludovi- 

 ciana) the breast patch and under wing coverts are 

 bright rose red, while exactly the same areas in the 

 black-headed grosbeak (H. melanocephala) are a clear 

 gamboge or lemon-yellow. As if still more emphatically 

 to emphasize the fact that this yellow was really a more 

 primitive stage of the red, the females of both species 

 have these parts colored a paler yellow. The fork-tailed 

 flycatcher (Milvidiis tyrannus) has the crown patch a 

 bright lemon-yellow, while the crown patch of the 

 scissor-tailed flycatcher (M. forficatus) is scarlet. So also 

 the kingbird (Tyrannus tyrannus) has a crown patch of 

 orange-red. In the gray kingbird (T. dominicensis), 

 according to Ridgway's Manual, it is orange colored, 

 while in the thick-billed kingbirds {T. crassirostris) it is 

 lemon-yellow. In this genus then, the stage of transi- 

 tion from red through orange to yellow is present. 

 Among the woodpeckers the crown patch is ordinarily 

 red, but in three-toed woodpeckers (Picoides) it is 

 yellow. 



The brilliant red of the scarlet tanager (Piranga ery- 

 thromelas) is replaced in the western tanager (P. ludovi- 

 ciana) to a large extent by yellow, the scarlet being 

 developed in the latter species in limited areas. The 

 females and young of both are yellow. In the flickers, 

 which are so intimately related, as shown by their 

 habitual hybridization, the one species is yellow (Co- 



