The Bird Department 



By a. a. Allen- , Ph.D. 

 Assistant Professor of Ornithology, Cornell University, Itliaea, N. Y 



THE COLORATION OF BIRDS 



IF Y(JU have followed the hoarse song of the scarlet 

 tanager and found him perched on some dead branch 

 ablaze in the sunlight; if you have noted the emerald 

 back and ruby throat of the hummingbird as he flashed 

 through the garden; or if you have seen the indigo bird 

 change from pale to deepest blue and then to black, you 

 must certainly have begun to wonder at the marvels of 



A RUFFED GROUSE OX ITS XEST 



A good example of protective coloration. The grouse is " counter-shaded " and 

 its color pattern is similar to that of the sticks and dead leaves about it. 



bird coloration. Then if you have tramped the woods 

 and heard the grouse rumble from the roadside and the 

 woodcock go whistling from under your feet, or if you 

 have tried in vain to locate the vireo singing in the tree 

 top, you must have been struck with the law of Nature 

 that causes her children to be clothed so dififerently. For 

 the grouse and the woodcock and the vireo in their haunts 

 are as invisible to the untrained eye as though they were 

 but a part of the sticks and leaves that surround them, 

 while the tanagers and hummingbirds hold the eyes of even 

 the least observing. What, then, are the laws determining 

 that one bird shall be clad like the sun and his neighbor 

 like the soil? What is the reason for this brilliancy on 

 the one hand, and how is the concealment, on the 

 other, brought about ? 



W'e might first distinguish between the colors of a 



bird's plumage and the bird's coloration, because a large 



part of the coloration of most birds is not caused by 



actual pigments but more by the refraction of light 



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through the structure of the feathers. A scarlet tanager 

 is red in any light because the red is a pigment, but an 

 indigo bird or a bluebird is blue only by reflected light 

 when refraction occurs. The only pigments that have 

 been found thus far in the feathers of birds are reds, 

 yellows, browns, and black. Green pigment occurs in the 

 African plantain-eaters, but in other birds the green is 

 due to a yellow pigment overlaid with a superstructure of 

 microscopic longitudinal ridges or polygonal bodies that 

 refract the light. Blue and all the metallic colors are due 

 entirely to this process of refraction, the exposed portion 

 of the feather being coated with a transparent colorless 

 layer of extreme thinness (8/1000 of an inch) which acts 

 like a number of prisms in breaking up the rays of light. 

 Thus, when a blue feather gets wet or when the bluebird is 

 perched between one and the sun, it will appear only 

 black or brownish. 



Sometimes there is an excess of black pigment in the 

 feathers of a bird which will make it appear much darker 

 than the other members of the same species. This is called 



A MEAUUVV LARK AT ITS XEST 



Showing the white outer tail feathers which are called " flash colors " and serve 

 the bird in a protective way when pursued by hawks. 



melanism and is better known in the familiar example of 

 the black and gray squirrels, examples of both occurring 

 in a single litter of young without reference to sex or 

 vigor. The opposite of melanism, or albinism, is much 

 more frequent and is caused simply by an absence or 

 degeneration of pigment of all kinds. The not-infrequent 

 white robins and sparrows or mottled birds with patches 

 of white feathers are explained in this way and are due 

 to inbreeding or some other weakness. 



