BRITISH WARBLEKS 



the individuals in some parts of the globe, we can see that it 

 is more than probable that many districts, formerly inhabited, 

 would not be inhabited to-day. 



In applying this law of battle to the life-history of these 

 smaller species, I am only extending a principle which is 

 already recognised as a factor in the evolution of animal life. 

 But in positing territory as the primary cause of the struggles 

 I am departing from the prevailing opinion. And inasmuch, 

 therefore, as this is the point which is the more likely to be 

 disputed, it will be as well if we review once more, but 

 briefly, the evidence upon which it is based, and in so doing 

 we shall see how impossible it is to reconcile the facts with 

 the only other possible explanation, namely, that the females, 

 are the direct cause of the struggles. In the first place, then, 

 we have this fact established, that in the majority of instances 

 each individual male of the migratory species when it finally 

 reaches its destination, and each individual male of the 

 resident species when the sexual instinct commences to 

 develop, and in some cases throughout the year, remains 

 in a certain restricted area encompassed by well-defined 

 boundaries which it seems unwilling to cross. Next we 

 have the spectacle of these same males engaging in fierce 

 conflicts amongst themselves, and in the case of the migra- 

 tory species even before any females have arrived ; and 

 this one fact, if placed beyond dispute, would alone be 

 sufficient to show that the females are not the direct 

 incentive to the struggles. But as the plea of insufficient 

 observation may here be raised— and no one can deny that 

 a female skulking in the undergrowth might easily escape 

 detection — we will pass on to the behaviour of the males 

 after the females have unquestionably arrived, and we find 

 them still continuing to struggle after pairing has taken 

 place, after the nest is built, and even after incubation has 

 commenced, though with less and less determination as the 

 season advances ; and, moreover, we can observe that these 

 quarrels follow after, and not infrequently seem to be con- 



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