WOOD WARBLER
powers with unwearying zeal hour after hour, he now contents himself with spasmodic outbursts, slovenly executed, a peculiarity which he shares with certain other species. If the arrival of a female were in a preponderating number of cases coincident with a complete cessation of the song, some difficulties that lie in the path of an interpretation of the latter would be cleared away, but unhappily this is not quite an accurate statement of the facts. That a definite change in the song does occur is obvious, a change so pronounced that we can rely upon it as an indication of her presence. The female, though she has no song, is strikingly persistent in uttering her call note, which, loud and clear as it may be, is often difficult enough to locate. Of course she remains more or less within the confines of his territory, but at first not absolutely so, for she may wander into an adjoining one, and thus cause some confusion. The small plot of ground which by force of habit has come to be regarded by him as a headquarters is not necessarily sacred to her; as likely as not she may select for her nest a corner of the territory far removed from this particular spot, or even before the question of a nesting site has become a practical problem she may remain in a part of the territory some distance from his headquarters, and this may lead to interesting behaviour on his part. We have the headquarters on the one hand, and the female on the other, the old influence and the new. Now one would expect to find that the sexual instinct at this particular time would be sufficiently strong to dominate every other influence, but anxious as he is to approach her, he nevertheless seems unwilling at times, even for her sake, to desert his headquarters; to and fro he flies, following and playing with her in one corner, then returning for a while to his special group of trees, where, despite her appeals, he shows anxiety—in fact seems almost compelled to resign himself to his former habit. So here we have a piece of behaviour which, though apparently trifling, yields nevertheless by slow degrees only to the most potent of all instincts, the sexual.
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