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APPENDIX E 
whatever in saving them from their foes. The nearly uniform colored 
mice and shrews are exactly as difficult to see as the others. 
Again, take what Mr. Thayer says of hares and prong-bucks. Mr. 
Thayer insists that the white tails and rumps of deer, antelope, hares, 
etc., help them by “obliteration’’ of them as they flee. He actually 
continues that “when these beasts flee at night before terrestrial enemies, 
their brightly displayed sky-lit white sterns blot out their foreshortened 
bodies against the sky.” He illustrates what he means by pictures, and 
states that “in the night the illusion must often be complete, and most 
beneficent to the hunted beast,” and that what he calls “these rear-end 
sky-pictures are worn by most fleet ruminants of the open land, and by 
many rodents with more or less corresponding habits, notably hares” and 
smaller things whose enemies are beasts of low stature, like weasels, minks, 
snakes, and foxes; “in short, that they are worn by animals that are 
habitually or most commonly looked up at by their enemies.” Mr. 
Thayer gives several pictures of the prongbuck, and of the northern 
rabbit, to illustrate his theory, and actually treats the extraordinarily 
conspicuous white rump patch of the prongbuck as an “obliterative” 
marking. In reality, so far from hiding the animal, the white rump is at 
night often the only cause of the animal’s being seen at all. Under 
one picture of the prongbuck, Mr. Thayer says that it is commonly 
seen with the white rump against the sky-line by all its terrestrial 
enemies, such as wolves and cougars. Of course, as a matter of fact, 
when seen against the sky-line, the rest of the prongbuck’s silhouette is 
so distinct that the white rump mark has not the slightest obliterative 
value of any kind. I can testify personally as to this, for I have seen 
prongbuck against the sky-line hundreds of times by daylight, and at 
least a score of times by night. The only occasion it could ever have 
such obliterative value would be at the precise moment when it happened 
to be standing stern-on in such a position that the rump was above the 
sky-line and all the rest of the body below it. Ten steps further back, 
or ten steps further forward, would in each case make it visible instantly 
to the dullest-sighted wolf or cougar that ever killed game, so that Mr. 
Thayer’s theory is of value only on the supposition that both the prong¬ 
buck and its enemy happen to be so placed that the enemy never glances 
in its direction save at just the one particular moment when, by a combi¬ 
nation of circumstances which might not occur once in a million times, 
the prongbuck happens to be helped by the obliterative quality of the 
