and on tough, fresh-water clams with equal readiness, with an occasional frog 

 or fish to vary the hill of fare. Chipmunks and ground squirrels may live 

 largely on grasshoppers during the summer and lay up seeds for the fall and 

 spring. It is common knowledge that the house mouse and the Norway rat 

 eat any food that their human landlords may have on hand. Most of the 

 carnivores are restricted in their diet, but a few either live mainly on insects 

 or else have a more varied bill of fare, so that they can spread more widely 

 than most of their group. The skunk is one of those that is mainly insectivor- 

 ous and is therefore not as dependent upon its surroundings as are the weasels, 

 its close relatives. Coyotes feed largely on mice, rabbits and carrion and fill 

 a useful part in nature's program. Foxes, like dogs, have a varied diet, in- 

 cluding considerable vegetable material. Both coyotes and foxes have had 

 their undesirable qualities stressed and their desirable ones ignored by people 

 who wish to justify poisoning or exploitation. The insectivores and the bats 

 are widely distributed on account of their insect-eating habits. The factors 

 governing the range of the latter are of great interest to the ecologist, as their 

 power of flight and the fact that their food is generally distributed make them 

 independent of the barriers that limit the distribution of the other mammals. 



Problems of mammal coloration have long interested naturalists. As a 

 general rule, large wild mammals are one color all over, and that color is 

 usually agouti or some shade of brown. Since the world Vv-ar led to the 

 almost universal adoption of olive drab for field uniforms, the reason for the 

 survival of mammals similarly colored and the elimination of other patterns 

 and colors has become evident. Only when protected or domesticated by 

 man can the conspicuous animals survive. In the sem.i-domesticated, Alaskan 

 reindeer herds, white and partially white animals are becoming fairly numer- 

 ous. Just as the woodland and grassland mammals must be brownish in order 

 to survive, so in the arctic the white mammals may have been picked by 

 natural selection, since arctic bears, foxes, wolves and rabbits are all white. 

 An alternate theory, however, is that pigment is developed in response to, and 

 as a protection from, bright light, and that the arctic mammals, not being sub- 

 jected to intense light, are not stimulated to produce pigment. This theory 

 is also used to explain the lack of pigment in some cave animals. Various 

 environmental factors have been considered responsible for variation in color, 

 but attempts to prove this have seldom been conclusive. Some interesting 

 studies have been made on mammals of some of the southwest desert areas, 

 where white sand and black lava offer the utmost possible contrast. In general 

 it appears that where predators are common the isolated rodent groups tend 

 to match the background upon which they live. Also, as a general rule, light 

 color phases usually occur on a light colored habitat, such as sandy islands and 

 dunes, with apparently little correlation between light or dark color and the 

 other factors of the environment. Since these mammals produce similarly 



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