WOOD WARBLER
their territories from intrusion as the males of many another species. Conflicts occur both before and after the arrival of the females, and have their origin. I believe, in the question of territory; they take the form of a flying at and rapid pursuit of one another, and are more frequent after a female does arrive in a territory, possibly because the neighbouring males, if still in bachelorhood, find it then difficult to resist their natural inclination to approach her closely. I have already called attention to the struggles between the males of closely allied species regarding the question of territory, and it is necessary to refer to them again in connection with this species. The term, "struggle for existence," is held to embrace every adverse influence that an organism has to face; it does not necessarily imply an actual trial of strength between species and species, though it is always supposed that such does actually occur. But to obtain evidence by direct observation is no easy matter. We are apt to forget that processes in Nature, even those which in time lead to great results, work very gradually, and that all the evidence we can ever hope to obtain of some change in progress is supplied in just those details which in themselves appear to be of trifling importance. Now in the conflicts between the males of the same and closely allied species we seem to have genuine struggles, which, without any undue stretching of the imagination, may be expected to lead to appreciable changes. Are they, however, really genuine? I ask this question because of statements made, not infrequently, to the effect that combats between rival males are now only formal. It is somewhat difficult to understand what the term "formal" is here held to denote; does it mean that they are not conflicts, or that they are conflicts to which no meaning can be any longer attached? Why should it be thought that the conditions which necessitated a clashing of interests in the past are not present to-day? And what waste of energy if they no longer serve any purpose! For my part I believe that they are very real—the death of
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