32 BIRDS OF SOUTH DAKOTA 



CHANGES OF PLUMAGE 



The changes of plumage observed in Ptarmigans and 

 Snowy Owls are evidently cases of adaptive coloration; but 

 there are other cases where such adaptation is not so evident. 



The male Goldfinch is bright yellow with black cap, wings 

 and tail in summer, but in winter he is scarcely distinguishable 

 from his mate. Many think these birds migrate south in au- 

 tumn, whereas they are annual residents. They are little noticed 

 in winter because males, females and young all look practically 

 alike. Is this protective coloration? It is true, of course, that 

 the male's bright yellow summer dress would make him a marked 

 object in the bare winter landscape, whereas the unobtrusive, 

 sparrow-like plumage of the females and young permits these 

 birds to feed by the half dozen on sunflowers and weeds in win- 

 ter almost unobserved. 



If the above suggestion regarding protective coloration be 

 correct, several other birds must be put in the same class. Be- 

 fore the Bobolinks go south the males have lost their glowing 

 white, buff and black and have taken the colors of the females 

 and young. They may be seen in late summer gathered in small 

 flocks perched on wire fences that run through meadows. They 

 are scarcely recognized as Bobolinks. The song is gone; the 

 wedding dress of the male has faded away; they are now pre- 

 pared for the southern journey, and are all dressed in "khaki," so 

 as to be as little observed as possible by enemies. 



The flaming coat of the male Scarlet Tanager disappears 

 in autumn and, although his wings and tail remain black, his 

 body takes on the olive green of the female. 



These seasonal color changes are not very well under- 

 stood. Of course, all birds molt their entire plumage after the 

 nesting season; some molt their whole plumage again in the 

 spring ; others molt their body feathers in spring ; while some do 

 not molt even all their body feathers. Changes which come by 

 molting are easily understood, but the above changes do not al- 

 ways come by molting. Some have thought that the feathers 

 change their pigment ; others that the tips of the feathers, which 



