112 SEA-BIRDS 



of the great blackback, and in Greenland the Iceland gull the place 

 of the herring-gull. Their place in nature seems to be exactly the same, 

 and their behaviour and function as a member of the cliff-community 



is identical. 



Other birds not yet mentioned which prey upon sea-birds of the 

 North Atlantic community are the bald, white-tailed, and even golden 

 eagles; and sometimes the snowy owl and the eagle-owl. and the gyr- 

 falcon. The long-tailed skua is not a predator of breeding sea-bird 

 communities, but pursues terns and kittiwakes at sea to a certain 

 extent in the off-season. The same is largely true of the pomarine 

 skua, though this does occasionally take young sea-birds on the 

 breeding-ground. Of course there are many other bird predators 

 which have occasionally picked up sea-birds in the course of their 

 hunting operations. Examples are: the merhn (which has taken a little 

 tern), common buzzard (which has taken a guillemot and often 

 young Manx shearwaters), marsh-harrier (a young black-headed gull) 

 goshawk (a common tern and an arctic (BriJnnich's) guillemot) 

 and the sparrow-hawk (a Leach's petrel and little tern). 



Of the mammal predators of the North Atlantic sea-birds quite 

 a formidable list could be compiled if we were to include every animal 

 that had ever been seen to eat a sea-bird. The list would certainly admit 

 the polar bear, the arctic wolf, the arctic fox, the red fox of the Old 

 World and the red fox of the New World, the otter, the stoat, the 

 killer- whale, the harp-seal of Newfoundland, and possibly the "black" 

 rat {Rattus rattus), as well as the abundant brown rat {R, norvegicus). 

 It is a commonplace that in Spitsbergen and Greenland, and no 

 doubt in other parts of the Arctic, the presence of arctic foxes forces 

 the sea-birds to occupy the more inaccessible ledges of the cliffs; 

 and they are quite important predators of the more vulnerable occu- 

 piers of the edges of the colonies. In Britain there are foxes on very 

 few islands, but the sea-bird stations on the mainland, notably that 

 at 016 Mor in north Sutherland near Cape Wrath, are harried by foxes. 

 Indeed, the foxes of C16 Mor have their cairn at the top of the most 

 important bird cliff. 



Undoubtedly the only really serious mammal predator of the 

 North Atlantic sea-birds is the rat, and we believe it is the only sea- 

 bird predator which can really be said to have made a significant 

 difference to the status of certain species. It is an introduced species, 

 not yet in a balanced ecological relationship with its prey where it 

 comes into contact with certain burrowing sea-birds. To give an 



