NATURAL SELECTION AS APPLIED TO BIRDS 323 



appearance of the persecuted, whereby they have come either 

 to resemble inanimate objects, or to assume a resemblance to 

 species which, from one cause or another, are too respected, or 

 too feared, to suffer molestation. 



The evolution of this " apatetic " coloration, as it has been 

 called by Professor Poulton, presents, as we have just indicated, 

 several more or less distinct phases. And of these the colours 

 which he calls " cryptic colours " are extremely well developed 

 among birds ; they are " colours which conceal an animal by 

 rendering it difficult to distinguish from some part of its vege- 

 table or mineral environment ". 



But these cryptic colours may serve two opposite ends — 

 they may either conceal a bird from its enemies, when they are 

 said to be " procryptic colours," or they may enable a pre- 

 daceous species, to approach its prey unobserved, and such 

 colours are known as " anticryptic ". 



Procryptic coloration has been brought to a pitch of marvel- 

 lous perfection in such birds as the Bitterns, for example, but, 

 it is to be noted, this peculiar coloration is invariably associated 

 with posturing of some kind. The Common Bittern of Great 

 Britain {Botaurus stellaris) — alas! no longer common — may be 

 made to serve as an illustration of this device. Haunting reed- 

 beds, the general hue of the plumage of this bird is buff, 

 streaked with black in such a way that the streaks may be 

 made to simulate the colour of the dark space between reed- 

 stems which are represented by the buff areas. On alarm the 

 bird straightens itself out so that the head, neck and spine form 

 one vertical line pointing skywards. Thus posed the bird re- 

 mains absolutely still, till danger is past ; the chances of detec- 

 tion amid such surroundings being infinitely remote. How 

 difficult this disguise is to detect has been told of the Little 

 Bittern {Ardetta involucris) of Argentina by Mr. W. H. Hudson, 

 " One day," he says, "... when out shooting, I noticed one of 

 these Herons stealing off quickly through a bed of rushes, 

 thirty or forty yards from me : he was a foot or so above the 

 ground, and went so rapidly, that he appeared to glide through 

 the rushes without touching them. I fired . . . and thinking 

 that I had killed him, I went to the spot. It was an isolated 

 bed of rushes I had seen him in ; the mud below, and for some 

 distance round was quite bare and hard, so that it would have 



