246 WARFARE BETWEEN DIFFERENT SPECIES 



to maintain both themselves and their families, 

 it is clear that the area these Reed-Buntings 

 occupied was in excess of that which they 

 would have required if they had been the sole 

 inhabitants. And such often appears to be 

 the case. Many a Warbler allocates to itself 

 a space of ground more than sufficient to supply 

 it with all that it needs ; so, too, does the Finch, 

 or the Pipit, or the Falcon — if we take no 

 account of kindred species. Thus there is 

 reason to believe that, by limiting the number 

 of individuals in a given locality, this apparently 

 wasteful expanse of territory is serviceable in 

 that it provides against the pressure of the bird 

 population upon the available means of support 

 becoming too great. But though a reduction 

 in the numerical standing of the different species 

 would certainly follow from any increase in 

 the area occupied by the respective individuals, 

 and with even greater certainty would place 

 them in a more secure position as regards their 

 supply of food, yet, when we remember how 

 large a number are dependent -^upon a supply 

 of insect life for their young, we can understand 

 that it would not alone be a sufficient safeguard 

 against the dangers attendant upon over- 

 crowding. It is here, I believe, that we shall 

 find the true explanation of the hostility ; it 

 roughly insures that the number of pairs in 

 any given area does not exceed the a,vailable 

 means of support, and indeed it is difficult to 

 imagine how such uniformity of distribution 

 as would free the young from the risk of 



