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 
