110 BRITAIN^S BIRDS AND THEIR NESTS. 



mentioned, we may name a few which have a permanent 

 coloration suited to a snowy environment : Arctic Hare, 

 Polar Bear, Greenland Falcon, Snowy Owl. There are 

 also some others. The two last-named are winter rarities 

 in the British Isles ; both are large birds of prey with a 

 plumage mainly white, and flecked with light brown. 



Now all these, birds and mammals, whether the snow- 

 garb be permanent or seasonal, may be divided sharply 

 into two classes — the predaceous, and those preyed upon. 

 The former class includes the Bear, the Fox, the Falcon, 

 and the Owl ; the latter, the Hare, the Ptarmigan, and the 

 WiUow-Grouse. In one set the coloration is aggressive — a 

 cloak to conceal attack ; in the other protective — a means 

 of escape. Thus, as one writer has graphically put it, ' The 

 Ptarmigan may be crouched upon a di'ift, but it must 

 ever be on the alert, lest from amid the snowflakes a 

 white death come suddenly upon it. Nature is terribly 

 just in her plan of life's battles.' 



THE BLACKCOCK, OR BLACK=GROUSE 



(Tetrao tetrix). 



Plate 36. 



As in the case of the RufF and the Reeve, the male 

 and the female of this species are generally known by 

 quite distinct names — ' Blackcock ' and ' Grayhen.' We may 

 speak of them collectively as ' Black-Grouse ' or ' black- 

 game,"" or apply the name of the male to the species. 

 The difference in name is an indication of the unusually 

 great difference between the plumage of the sexes, 

 perhaps more marked than in any other British bird. 

 It is not merely a matter of colour — more striking 

 differences of that sort occur among the Ducks ; but the 



