BIOLOGICAL VALUE OF THE WARFARE 245 



8 '5 square yards in the space allotted to each 

 individual. The pressure of the bird population 

 upon the means of support would then have 

 been materially increased ; and not only the 

 Buntings, but the Warblers, Pipits, and all 

 the rest would have suffered. But the result 

 would have been the same if, instead of 

 the four additional male Reed-Buntings, four 

 males of other kinds had been allowed to 

 enter the marsh, and we can multiply the 

 number four until we arrive at a point when 

 the means of subsistence would no longer have 

 been adequate for the adults, still less for the 

 young. If, then, there were nothing to pre- 

 vent this happening, many of the birds in that 

 marsh would have no chance of rearing their 

 young successfully. Hence, if the territory is 

 adequately to serve the purpose for which we 

 believe it has been evolved, some provision must 

 have been included in the system to meet the 

 difficulty. 



There are three ways by which this may have 

 been accomplished — indirectly, by increasing the 

 size of the area occupied by each individual, 

 and thereby reducing the relative number of 

 each species ; or directly, by rendering the 

 fighting instinct of the bird susceptible to 

 stimulation by individuals of other species; or, 

 possibly, by a combination of the two. There 

 were four pairs of Reed-Buntings in the marsh, 

 and their territories covered the whole of it. 

 But inasmuch as other insectivorous birds were 

 established there also, and found sufficient food 



