BIRDS OF NEW YORK STATE 



149 



mage are acquired merely by wearing off these gray edges. The 

 black bib of the male house sparrow is a good example. 



House sparrow in winter and early spring Nu Spl 

 House sparrow in summer Nu Spll 



4 Dichromatism 



In a few species of birds there are two color phases irrespective 

 of age, sex or season. They often occur in the same brood of 

 young. The red and gray phases of the screech owl are the best 

 example. It is probable, likewise, that the Cory's least bittern 

 represents a color phase of the least bittern. 



Screech owl, gray phase Nu OwS 



Screech owl, red phase Nu OwS7 



5 Albinism 



In individuals of any species a weakness in .pigment is likely 

 to occur resulting in pale or white feathers. Pure albinos, with 

 no pigment whatever, occasionally occur in all species. 



Normal and albino robins Nu Ro9S 



6 Protective coloration 



One of the most interesting phases of the coloration of birds is 

 that of "protective coloration." The majority of birds are incon- 

 spicuous in their natural haunts that they may more easily escape 

 their enemies. Nature renders them inconspicuous in a variety 

 of ways. 



a Counter shading 



The most universal method by which birds are inconspicuously 

 colored is • called "counter-shading," which may be briefly 

 explained thus: All solid objects out of doors cast shadows on 

 their underparts. So universally is this true that the eye depends 

 upon the shadow to judge whether an object is a solid or a plane. 

 If the shadow is counteracted by lighter coloring in direct pro- 

 portion to the amount of the shading, the object will appear flat, 

 apparently lose its solidity and cease to stand out away from its 

 background. If the object at the same time is the color of the 

 background it will apparently become a part of it and riot be 

 noticed as an entity. In the accompanying photographs of 

 models, two blocks of exactly the same size and colored uni- 

 formly dark were placed on a gravel walk. The great bird artist 

 Louis A. Fuertes then added white paint to the underparts of 



