SEA-BIRDS 133 



Of the marine birds the great blackback does not usually venture as 

 far out as the lesser blackback and herring-gulls. (We have seen 

 a few lesser blackback and herring-gulls at Rockall, which is 191 miles 

 west of the St. Kilda islands and nearly 300 miles north-west of Ireland; 

 it is however "land" and it lies on a fishing bank of its own.) In 

 the parts of the North Atlantic most familiar to British and American 

 ornithologists the most typical inhabitants of the marine or offshore 

 zone are the razorbill, guillemot, lesser blackback, herring-gull,puffin 

 and gannet; in the tropics the brown booby. The last three of these — 

 the puffin, gannet and brown booby — are perhaps more oceanic 

 than the others and more inclined to be found also in the next zone, 

 which Wynne-Edwards names pelagic but which we shall generally 

 here call oceanic. 



This zone contains some all-the-year-round birds, and some seasonal 

 birds. The Manx shearwater, which is also very much an inhabitant 

 of the offshore zone, is found here in greater numbers than early 

 workers have recognised, and can also certainly be classified as an 

 oceanic bird. Among the important seasonal birds are the arctic 

 tern, which makes a twice-yearly crossing of the Xorth Atlantic, the 

 four species of skuas, which also make twice-yearly seasonal crossings, 

 and the two species of ocean-wintering phalaropes. The all-the-year- 

 rounders, i.e. species which use the open ocean at all times when they 

 are not actually engaged in breeding and return to it when they are 

 off-duty, even during the breeding-season, include almost all the 

 tube-nosed birds; particularly in the North Atlantic, Leach's petrel, 

 the storm-petrel, the fulmar, the Tristan great shearwater, the North 

 Atlantic shearwater, the sooty shearwater, Bulwer's petrel, the frigate- 

 petrels and the gadfly petrels. The only oceanic gull is the kittiwake. 

 The little auk might fall into this category, but it has a food-connection 

 with the ice-front which necessitates a rather special definition of its 

 distribution. In general, as Wynne-Edwards points out, each of the 

 three chief families of northern sea-birds is the main possessor of one 

 of these three zones. The gulls largely possess the inshore zone, the 

 auks largely the offshore zone, the tubenoses the oceanic zone. 



During the present century a number of ornithologists have crossed 

 the North Atlantic and plotted accurately the sea-birds which they 

 encountered, checking their position with the ship's log. Recently 

 E. M. Nicholson (1950,1951) has made a classification of the whole of 

 of the North Atlantic into ten-degree blocks, for which he has provided 

 a practical and easily memorable nomenclature (Fig. 55^ p. 291). 



