418 THE OWLS 



Whether heavily or slightly barred, the general effect of this 

 plumage is whiteness : and there can be no doubt but that it confers 

 a distinct advantage on the bird, inasmuch as it enables it to occupy 

 any point of vantage wherefrom to survey the land when on the look- 

 out for prey without being itself detected, since the plumage harmon- 

 ises for the greater part of the year, at any rate, with the mantle of 

 snow which is spread over the whole country. By the time this 

 disappears the capture of prey becomes an easier matter, being more 

 abundant, and it is probable that even then, from its habit of sitting 

 motionless, it is by no means conspicuous. But we naturally ask, Is 

 this whiteness due to the direct action of natural selection, eliminating 

 all but the whitest owls, or is it due rather to the effect of cold, which 

 is inimical to the secretion of pigment? In other words, Is the 

 coloration due to the selection of variations in the direction of white- 

 ness, or is it a physiological reaction to physical stimuli ? In either 

 case, it may be argued, natural selection is the arbiter, on the one 

 hand eliminating unfavourable pigmental variations, on the other, 

 variations in which the metabolism is unaffected by cold, for it seems 

 certain that whiteness is essential to survival in these regions for this 

 species, and this whiteness is a highly specialised character induced 

 by selection. The same factors, whatever they may be, have brought 

 about the whiteness of the ptarmigan and the Arctic hare, on which 

 the snowy-owl largely feeds. But this is what we should expect. It 

 is the unwary which are taken, from among the victims; it is the 

 restless owl which goes hungry from among the slayers. Movement, 

 on either side, betrays. Strong contrast with environment, on either 

 side, means death, either by violence or starvation, as the case may be. 

 If only the ptarmigan, grouse, and hare are protectively coloured, then 

 the fox and the owl must perish, for they will give warning of their 

 approach long before they come within striking distance. If, on the 

 other hand, only the fox and owl wear this garment of invisibility, then 

 sooner or later the ptarmigan and hare will vanish. 



There is one other point demanding notice, and this concerns the 



