I OUR GRAY SQUIRRELS 29 



effect of natural selection in adapting the animal 

 (in color) to its surroundings, by tending to make 

 it less conspicuous in an exposed than in a con- 

 cealed habitat, is also to be considered here. 



Quite distinct from this, however, seems to be 

 the tendency to melanism, which is so strongly 

 marked in several of our sciurids. Among flying- 

 squirrels, red squirrels, and chipmunks, a black 

 one is as rare as an albino — probably more rare ; 

 but in the cases of the gray and the fox squirrels 

 black examples are extremely common in some 

 parts of the country, and are popularly considered 

 a wholly separate species. But no such rule of 

 climate as mentioned above seems to control this 

 phenomenon, since black or dusky forms of both 

 species are as likely to be southern as northern in 

 their habitat. Where melanism occurs, it is likely 

 to prevail over a considerable district, sometimes 

 nearly if not quite to the exclusion of squirrels of 

 the normal tint. This shows that, though sporadic, 

 it "runs in families," descending from parents to 

 young ; yet not inevitably so, for many litters pro- 

 duced by black parents will contain a member or 

 two gray, or red, or grizzled, and black and normal 

 individuals mate freely. The "color-line" is not 

 drawn in sciurine society. Black ones, however, 

 are never, or very rarely, seen east of the Hudson 

 River ; and, furthermore, the northeastern black is 

 often rusty or brownish in tone, rather than pure, 

 especially in its summer pelage. Curiously enough 



