BRITISH WARBLEBS 



a fatal struggle ; and if a territory is won a mate is won also. 

 No fact has impressed itself upon me more strongly than 

 this latter, for we know that not all the males, nor all the 

 females, arrive at the same moment, and so it happens that 

 one male will commence to breed a week, a fortnight, or 

 perhaps a month before its neighbour; yet notwithstanding 

 this difference in time, which, when we take into consideration 

 how short is the whole period of sexual reproduction, is a very 

 considerable one, I have not found a single case of a male 

 securing a territory and not ultimately securing a mate. It 

 may be urged that the evidence of so small a number of 

 species is insufficient, but let it be remembered that I have 

 purposely studied species very widely separated in the phylo- 

 genetic tree, and have found a similar law in operation ; and 

 if it were not a general rule that territory and reproduction 

 were synonymous, some instances, some evidence at least, 

 ought to have come under my notice. It seems evident, 

 therefore, that a territory is essential to the individual male if it 

 is to attain to reproduction, and inasmuch as the final appeal 

 for possession is to the law of battle, we can well understand 

 that on the average it will be the stronger birds that will 

 leave offspring to inherit their congenital tendencies; the 

 weaker will either perish, or which amounts to the same 

 thing not attain to reproduction. At the same time we 

 must not always assume that the bird that is defeated is, 

 although weaker, not so fit to reproduce, or not so likely to 

 produce healthy offspring, since it is quite conceivable that 

 up to a certain age the older birds will have an advantage, 

 due solely to laws of growth, but, on the average, it will 

 be the stronger individuals that leave offspring. Thus there 

 is constantly at work each recurring spring a process of 

 elimination, whereby the species is not only maintained in 

 a healthy condition, but is gradually being brought to a 

 greater state of perfection. And so in its immediate results, 

 the law of territory is nothing more than a form of natural 

 selection. Before going further, however, it will be necessary to 



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