Cfje ^uliubon .Societies! 



SCHOOL DEPARTMENT 



Edited by A. A. ALLEN. Ph.D. 

 Address all communications relative to the work of this 

 department to the Editor, Cornell University, Ithaca, N. Y. 



THE COLORATION OF BIRDS 



If you have followed the hoarse song of ihe Scarlet Tanager and found him 

 perched on some dead branch ablaze in the sunlight; if you have noted the 

 emerald back and the ruby throat of the Hummingl)ir(l as he Hashed through 

 your garden ; or if you have seen the Indigo Bunting change from pale to deepest 

 blue and then to black, as you moved around him, you must certainly have 

 begun to wonder at the marvels of 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 impressed by that law of 

 Nature that causes her children to be clothed so differently. For the Grouse 

 and Woodcock and the Vireo in their haunts are as invisible to the untrained 

 eye as though they were but a part of the twigs and leaves that surround them, 

 while the Tanagers and Hummingbirds hold the eyes of even the least ob- 

 serving. 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 l)rilliancy, 

 on the one hand, and how is the concealment, on the other, brought about? 

 Certainly there is enough of interest in the coloration of birds to make it worth 

 our while to analyze the problem in some detail. 



Let us begin by considering the actual colors which make up the birds' 

 coloration, for they are very different in their origin as well as in their general 

 effect. One who ordinarily thinks of the colors of animals as produced by 

 pigments or color granules deposited within the skin or hair will be surprised by 

 the small percentage of the colors of birds' feathers that are produced in this 

 way. In fact, there are, in ordinary birds, supposed to be but three ])igments in 

 in any of the feathers: reds, yellows, and browns. A green pigment occurs 

 the African Plantain-eaters, but in other birds the green is due to a yellow 

 pigment overlaid with a structure that refracts the light. Blues 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-ioooth of an inch) which acts like a number of prisms in breaking up the rays 

 of light. A Scarlet Tanager is red in any light because the red is a pigment, but 

 an Indigo Bunting or a Bluebird is blue only by reflected light, when refraction 

 occurs. Thus, when a Bluebird gets wet or when it is perched ])etween one 

 and the sun, it will appear only l^lack or brownish. This fact adds to the 



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