Page:The British Warblers A History with Problems of Their Lives - 7 of 9.djvu/51

 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, what 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 was 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