18 INTRODUCTION 



enable us to picture, on the one hand, the 

 precarious situation of an individual that was 

 incapable of winning or holding a position at 

 the accustomed breeding station, and, on the 

 other, the plight of the species as a whole if 

 each one exercised authority over too large an 

 area. With the majority of species it is difficult 

 to do this. So many square miles of suitable 

 breeding ground are inhabited by so few Reed- 

 Buntings that, even supposing certain members 

 were to establish an ascendency over too wide 

 an area, it would be impossible to discover 

 by actual observation whether the race as a 

 whole were being adversely affected. Com- 

 petition doubtless varies at different periods and 

 in different districts according to the numerical 

 standing of the species in a given locality and 

 according to the numerical standing of others 

 that require similar conditions of existence ; at 

 times it may even be absent, just as at any 

 moment it may become acute. These examples 

 show how profoundly the evolution of the 

 breeding territory may have been influenced by 

 relationships in the inorganic world, and they 

 give some idea of the intricate nature of the 

 problem with which we have to deal. 



I mentioned that the first visible mani- 

 festation of the revival of the sexual instinct 

 was to be found in the movements under- 

 taken by the males at the commencement 

 of the breeding season. Such movements are 

 characterised by a definiteness of purpose, 

 whether they involve a protracted journey of 



