BIOLOGICAL VALUE OF THE WARFARE 247 



exposure could be obtained without some such 

 control. 



Some birds, however, have no difficulty in 

 finding the necessary food for their young, yet 

 have great difficulty in finding a station where 

 they can rear their young in safety ; and the 

 area each one occupies has been reduced 

 to the smallest proportions in order that the 

 maximum number can be accommodated. Here, 

 any increase in the size of the territory would 

 inevitably lead to the extinction of the race, 

 so that nothing stands between failure and 

 success except the ability of the bird to defend 

 its territory. If we study the bird population 

 at one of the breeding stations on the coast, 

 we find, generally speaking, that each kind of 

 bird inhabits a particular portion of the cliff; on 

 the lower ledges are the Guillemots and Kitti- 

 wake Gulls ; higher up are Razorbills and 

 Fulmars, and at the top, where the cliff is 

 broken and the, face of the rock covered with 

 turf and soil, the Puffin finds shelter for its 

 egg. At the same time there is much over- 

 lapping ; the kind of ledge that suits a Razor- 

 bill is equally suitable for a Guillemot or a 

 Fulmar, and so, no matter how successful the 

 Razorbill may be in establishing a territory 

 and preventing intrusion upon it by other 

 Razorbills, it will be all to no purpose if it 

 allows itself to be jostled out of its position 

 by a Fulmar. Hence, inasmuch as breeding 

 stations are limited and competition for territory 

 so severe, only those forms in which the fighting 



R2 



