BRITISH WARBLERS
territories work their way towards the same boundary simultaneously. As they approach the boundary the song becomes more frequent and very hurried, their whole attitude being one of great excitement. As they approach still more closely, this excitement increases, their wings are jerked about, the song deteriorates into a few notes rapidly uttered, they still pretend to hunt for food in a half-hearted sort of manner, but all the time it is evident that each one is keeping a close watch upon the other's movements: then the climax is reached, they dart at one another, tumbling over and over in the air, their bills clicking loudly; and, their honour appearing to be satisfied, they immediately retire to their respective territories. The final scene is not, however, always reached, for just as the excitement seems to be at its highest point, one of them commences to move in the opposite direction. Whereever there are territories adjoining, this scene, or a scene similar to what I have described, is of common occurrence, frequently being enacted by the same individuals many times during the same morning.
Whether these scenes are prompted by pugnacity or whether they are simply due to love of play I cannot tell, but there is most probably some relation between them and the importance to each individual of his respective territory. As their behaviour shows, each one is undoubtedly conscious of the approach of his rival for some distance before the boundary is reached. Whether the fight or game only takes place when one actually crosses the boundary I have not been able to determine.
A male that has recently arrived often passes through the territory already adopted by some earlier arrival, and his behaviour under these circumstances is instructive. He creeps amongst the bushes low down, almost in the undergrowth, not singing, but occasionally uttering a note, apparently anxious to keep out of sight. It is, however, seldom that he remains long undetected by the keen eye of the owner, who immediately starts in pursuit, darting after him with
10
