REED WARBLER
are confronted. It almost seems as if Nature had thus supplied us with a key to some of the mysteries of their existence. The married life of the resident species is so gradually unfolded each recurring season before our eyes, that we know not with any certainty at what point sexual development commences, and we can seldom indicate the precise moment at which that mutual attraction between the sexes occurs which ultimately leads to reproduction. But in the case of the migratory species the conditions happily are different, for since the spring migration is undertaken for the purpose of procreation, it is probable that the stimulus to that long and arduous journey is the fact that the initial stage of the development of the sexual organs has commenced. Moreover, males arrive before the females, and this fact is of immense assistance in helping us to trace out the true meaning of much of their behaviour.
I found, then, that many of those males that were the first to reach a certain district were not passing travellers only, seeking out new woods or new swamps, and leaving their places to be filled by later arrivals, but that they remained more or less in that locality in which they had settled upon their arrival; and further observation went to show that this locality was narrowed down to a certain territory, in which the bird remained and sought its food, and which possessed definite boundaries adhered to with remarkable precision, and often, indeed, with an accuracy almost beyond belief. Furthermore I found that, when two males arrived more or less at the same time in the same locality, a battle often ensued, equally as desperate as those which occur amongst many of the resident species at this season of the year; but inasmuch as the females had not at that time arrived, it was clear that they were not the direct cause of the quarrels; and, finally, that in the case of adjoining territories whenever a male crossed the boundary at any time during the period in which the territories were adhered to, its action was generally resented by the other male, and often led to a struggle. With
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