MARSH WARBLER 



back and head, spreads and jerks his tail, singing excitedly 

 whilst doing so, whereupon the intruder usually retires and 

 the commotion ceases. I have seen a male on the approach 

 of a Sedge Warbler spread out his wings and tail in a similar 

 manner. In many cases in which a male intrudes upon a 

 neighbouring territory, the owner, flying to the same tree, 

 settles beside him, but does nothing further in the way of 

 active expostulation ; yet this seems to have the desired effect, 

 for the intruder as a rule retires and the object of the owner is 

 thereby achieved. It must not be forgotten that the retreat of 

 the intruder is all that is required. And that this should 

 often be accomplished without recourse to battle is an 

 advantage to the species as a whole. Two males with 

 territories adjoining may be equal in strength; they may 

 have been compelled to fight earlier in the season when 

 challenged by other claimants to respective positions, or they 

 may not have had to face a rival. Supposing, however, that 

 they are of equal strength and both equally fitted to reproduce, 

 w T hat effect could incessant and severe struggles have other 

 than a harmful one ? Energy would thereby be wasted, and 

 no inconsiderable strain imposed upon the physical strength of 

 the birds just at the moment when a greater strain w T as being 

 placed upon their nerve force, and this could scarcely fail to 

 reflect itself upon the strength of the offspring. He, therefore, 

 who makes a study of some particular species, and watches the 

 behaviour of males with adjoining territories, expecting to see 

 constant and earnest struggles, expecting, whenever the males 

 approach one another closely, to hear and see unmistakable 

 signs of conflict, expecting even to witness with but little 

 difficulty a vanquished male succumb to its injuries, will 

 certainly be disappointed, and he will do well to bear in mind 

 this fact, that, for the welfare of the species, conflicts could 

 easily become too frequent and could even be carried too far, if 

 Nature had not ordained otherwise. 



What with one species and another there is thus frequent 

 commotion. The excitement, as mentioned, takes the form of 



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