504 APPENDIX E 



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 "" nmrking. 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 farther back, or ten 

 steps farther 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 prongbuck 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 combination of circumstances which might not 

 occur once in a million times, the piongbuck happens to be helped 

 by the obliterative eiuality of the white rump mark. Now, in the 

 first place, the chance of the benefit happening to any individual 

 prongbuck is so inconceivably small that it can be neglected, and, 

 in the next place, in reality the white rump mark is exceedingly 

 conspicuous under all ordinary circumstances, and, for once that it 

 might help the animal to elude attention, must attract attention 

 to it at least a thousand times. At night, in the darkness, as 

 anyone who has ever spent much time hunting them knows, the 

 white rump mark of the antelope is almost always the first thing 

 about them that is seen, and is very often the only thing that is 

 e\er seen ; and at night it does not fade into the sky, even if the 

 animal is on the sky-line. So far as beasts of prey are guided by 



