APPENDIX E 497 



flat on the ground like a hare, and its white tail is almost invisible, while 

 of course even the most low-creeping foe would not under such circum- 

 stances get it against the sky-line. When it skulks it moves off with 

 head and neck outstretched and tail flattened down with the white as 

 much obscured as possible. The white is never shown in conspicuous 

 fashion until the animal is frightened and no longer seeks concealment. 

 It then bounds off openly, crashing through the brush, with its white 

 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 



