species that make temporary excursions from their, territories. The male, on its return, flies as a rule direct to its special tree and sings. Sometimes, however, it settles upon the ground, not unfrequently accompanied by the female, and while there remains silent; but presently rising from the ground and deserting its mate, it flies to the headquarters and sings. Again, nearly every male at one time or another in the course of the season is aroused to action by the intrusion of a rival. The emotional tone of the owner of the territory is then raised, and the intruder is pursued and attacked; but this alone is not sufficient, it seems as if the chain of instinctive activities, when once aroused by appropriate stimulation, must pursue its course to the end—and the end in such a case is only reached and complete satisfaction only gained when the bird has not merely returned to his "headquarters" but has given vocal expression to his emotion. Finally, we must bear in mind these two facts, that the "headquarters" is occupied solely by the male—it forms no part of the life of the female—and that it is the male only that sings.
Many such subtle incidents of behaviour as the foregoing can be perceived but not readily described, and trifling though they may seem to be in themselves, yet in the aggregate they yield full assurance of a close relationship. The distant song of a male, or the presence of an intruding male, have also stimulating effects, though in somewhat different ways.
