BRITISH WARBLERS
down to her, and sometimes when very close warbles so quietly that the sound is scarcely audible a few paces away. During these scenes she may flap her wings whilst perched upon a branch, but more usually betrays her emotion by restless behaviour and by uttering various call notes. The presence of a third male evokes much excitement, the owner of the territory spreading and flirting his tail and even flying at the intruder. All this behaviour is clearly but a repetition of that which occurred earlier in the season, and my sole reason for repeating so much of what has already been described is to call attention to the lateness of the date, which requires some explanation.
An interesting feature of the period of sexual activity is the attitude adopted by the bird towards other species, more especially towards the Blackcap, to which it is closely related. It is the male who more frequently betrays emotion in the presence of a member of another species. Much excitement is caused by the intrusion of a Blackcap, and, in a lesser degree, of a Whitethroat or a pair of Whitethroats, in his territory, and the scenes which ensue remind one forcibly of those which result from the intrusion of a neighbouring male of his own species. We listen to a similarly violent use of the vocal powers into which is infused much feeling tone; we see similar pursuits taking place, culminating in a flying together with snapping of bills, and observe similar excitement reflexes. What is the biological significance of such behaviour? If it has no meaning, but is only a manifestation of surplus energy, then it must clearly be included in the category of "play." But in observing the birds under these peculiar circumstances, one is impressed with the persistent striving towards some end which is the accompaniment of such behaviour, and we cannot regard as meaningless behaviour which is so frequent in occurrence, so suffused with feeling tone, and so productive of motor reactions which are customarily associated with feelings of displeasure. What then can the meaning be? Surely the fact that it is a closely related form that is the
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