EXTENSION OF BREEDING RANGE 19 



some hundreds of miles or merely embrace a 

 parish or so in extent, and that purpose is the 

 acquirement of a territory suitable for rearing 

 offspring. They are thus directly related to the 

 territory, and the question arises as to whether 

 their origin may not be traced to such related- 

 ness. So long as we fix our attention solely 

 upon the magnitude of the distance traversed 

 the suggestion may seem a fanciful one. Never- 

 theless, if the battles between males of the 

 same species are directly related to the occupa- 

 tion of a position suitable for breeding purposes, 

 if those which occur between males of closely 

 related forms can be traced to a similar source, 

 if the females take their share in the defence 

 of the ground that is occupied, if, in short, the 

 competition is as severe as I believe it to be, 

 and is wholly responsible for the strife which 

 is prevalent at the commencement of the 

 breeding season — then such competition must 

 have introduced profound modifications in the 

 distribution of species ; it must have even 

 influenced the question of the survival of 

 certain forms and the elimination of others ; 

 and since the powers of locomotion of a bird 

 are so highly developed it must have led to 

 an extension of breeding range, limited only 

 by unfavourable conditions of existence. 



