APPENDIX E 557 



tail flaunted, and under such circumstances the white mark is extremely 

 conspicuous. 



Indeed I feel that there is grave ground to question the general state- 

 ment of Mr. Thayer that "almost all mammals are equipped with a full 

 obliterative shading of surface colors; that is, they are darkest on the 

 back and lightest on the belly, usually with connected intermediate 

 shades." This is undoubtedly true as a statement of the coloration, but 

 whether this coloration is in fact obliterative needs further investigation. 

 Of course if it is obliterative, then its use is to conceal the mammals. Mr. 

 Thayer's whole thesis is that such is the case. But as a matter of fact, 

 the great majority of these mammals, when they seek to escape observa- 

 tion, crouch on the ground, and in that posture the light belly escapes 

 observation, and the animal's color pattern loses very much of, and some 

 times all of, the "full obliterative shading of surface colors" of which 

 Mr. Thayer speaks. Moreover, when crouched down in seeking to es- 

 cape observation, the foes of the animal are most apt to see it from above, 

 not from below or from one side. This is also the case with carnivorous 

 animals which seek to escape the observation of their prey. The cougar 

 crouches when lying in wait or stalking, so that it is precisely when it is 

 seeking to escape observation that its lighter-colored under parts are ob- 

 scured, and the supposed benefit of the "obliterative shading pattern" lost. 

 I do not intend without qualification to take ground one way or the other on 

 this general question; but it is certainly true that any such sweeping state- 

 ment as that quoted above from Mr. Thayer is as yet entirely unproved. 

 I have no doubt that in most cases animals whose colors harmonize with 

 their environment, and which also seek to escape observation by remain- 

 ing motionless when they think there is danger, are very materially helped 

 by their concealing coloration; but when this concealment is said to be 

 due to the obliterative shading as described by Mr. Thayer, it is certainly 

 worth while considering the fact that the so-called obliterative pattern 

 is least shown, or is not shown at all, at the only time when the animal 

 seeks to escape observation, or succeeds in escaping observation that is, 

 when it crouches motionless, or skulks slowly, with the conscious aim of not 

 being seen. No color scheme whatever is of much avail to animals when 

 they move unless the movement is very slow and cautious; rats, mice, 

 gophers, rabbits, shrews, and the enormous majority of mammals which are 

 colored in this fashion are not helped by their special coloration pattern at 

 all when they are in motion. Against birds of prey they are practically 

 never helped by the counter-shading, but merely by the general coloration 

 and by absence of movement. Their chief destroyers among mammals 

 such as weasels, for instance hunt them almost or altogether purely by 

 scent, and though the final pounce is usually guided by sight, it is made 

 from a distance so small that, as far as we can tell by observation, the 

 "counter-shading" is useless as a protection. In fact, while the general 

 shading of these small mammals' coats may very probably protect them 

 from certain foes, it is as yet an open question as to just how far they 

 are helped (and indeed in very many cases whether they really are helped 



