ORGANIC AND INORGANIC RELATIONSHIPS 15 



to the places suitable for breeding. Why does 

 the Reed-Bunting cling so tenaciously to an 

 acre or more of marshy ground, while the 

 Guillemot rests content with a few square feet 

 on a particular ledge of rock? The answer is 

 the same in both cases — to facilitate reproduc- 

 tion. But why should a small bird require 

 so many square yards, whilst a very much 

 larger one is satisfied with so small an area ? 

 The explanation must be sought in the con- 

 ditions of existence. The Reed-Bunting has 

 no difficulty in finding a position suitable for 

 the construction of its nest ; there are acres 

 of waste land and reedy swamps capable of 

 supplying food for large numbers of individuals, 

 and the necessary situations for countless nests. 

 But its young, like those of many another 

 species, are born in a very helpless state. For 

 all practical purposes they are without covering 

 of any description and consequently require 

 protection from the elements, warmth from 

 the body of the brooding bird, and repeated 

 supplies of nourishment. A threefold burden 

 is thus imposed upon the parents : they must 

 find food for themselves, they must affiord 

 protection to the young by brooding, and they 

 must supply them with the necessary food at 

 regular intervals. And their ability to do all 

 this that is demanded of them will be severely 

 taxed by the brooding which must perforce 

 curtail the time available for the collection 

 of food. 



Let us then suppose that the Reed-Buntings 



