EVOLUTION OP THE COLORS OF BIRDS. 133 



This first mode of change is doubted even by many- 

 ornithologists of to-day, and yet the testimony presented 

 in Yarrell's paper seems to be conclusive on the point. 

 To be sure, it does seem difficult to understand how a 

 feather, in which there is no circulation, in fact no life, 

 apparently, can alter its color. Mr. Yarrell tried the 

 experiment of marking certain feathers in a bird which 

 he suspected to be changing color, and succeeded in 

 actually observing the addition of pigment. He also 

 says: " On the breasts of several golden Plovers, some of 

 the feathers were entirely white, the colour peculiar to 

 all the feathers of that part of the bird in winter; some 

 were entirely black, being the colour assumed at the 

 breeding season; while others bore almost every possible 

 proportion of well-defined black and white on the same 

 feathers; from which it appears that the same cause of 

 particular colour in new feathers can also partially or 

 entirely change the colour of old ones." 



Mr. F. 0. Johnson first called my attention to the 

 tails of some Arizona hooded orioles (Icterus cucuUatus 

 nelsoni) in his collection. They represent various 

 stages of transition from yellow to black. I have since 

 examined all the specimens of this bird in the National 

 Museum and the American Museum of Natural History 

 in New York, besides a number in private collections, 

 and from this ample material cannot but conclude that 

 the transition in this species is by an addition of pig- 

 ment without moult. Plate VI shows a tail in a state 

 of change. The primitive color of the tail in this 

 species is yellow, but in the adult male entirely black. 

 The tail figured was of an immature male in changing 

 plumage. The feathers are still yellow for the most 

 part, but one has become almost completely black, only 

 a part of the tip being left yellow. In other feathers 

 little spots of black were visible, while in still others the 



