BRITISH WARBLERS 



reason, so far as we are able to judge, why, in many instances, 

 more members should not breed in proximity to one another 

 than actually do so at the present time. Have we not an 

 explanation in the constant struggle for territory — that 

 struggle which is such an essential to reproduction, a motive 

 force, as it were, dispersing the species in every direction? 

 But let this, which I have already pointed out, be remem- 

 bered, that the territories need in no sense be regarded as a 

 chain with numberless links, and that it is not essential for 

 every available plot of ground to be occupied before the species 

 can extend, but that by reason of the struggle being so relent- 

 less it must happen, and not infrequently, that an individual 

 will be unnecessarily urged to seek ground beyond the imme- 

 diate neighbourhood. 



Now there is no reason to believe that this struggle for 

 territory has only recently arisen. Possibly it has been 

 even more severe in the past. But if proof of its early origin 

 be required it can be found in this fact, that it is severally 

 common to and inseparable from the habits of widely separate 

 species. Therefore let us glance at the past history of an 

 imaginary species, and, bearing in mind the severity of the 

 struggle on the one hand, and the long periods of time on the 

 other, attempt to trace the course of events in so far as they 

 might have been affected by this law. We must suppose that 

 the species is of comparatively small numerical strength, and 

 of limited range, and, further, that a point has been reached 

 when the individuals that do not allow others to breed in 

 proximity to them have gained an advantage. Each recurring- 

 spring the conflict for territory would take place, causing an 

 extension in the breeding range. In some directions the con- 

 ditions of existence might be such as would make it impossible 

 for the species to survive, in others large areas might be 

 unoccupied, owing possibly to their being passed over un- 

 heeded, or to the individuals settled therein having been from 

 one cause or another exterminated and not replaced, and yet 

 in others the succession of breeding territories might be con- 



36 



