BRITISH WARBLERS
away and she must be the stimulus unless the emotion is spontaneous, arising. Ave know not how, from the sexual condition of the male. In either case the feelings which prompt the bird to action can scarcely be those of displeasure, and we have indisputable evidence that the movement of the wings can be associated with a pleasurable emotion, since the female nutters them at a moment when her desires are perfectly clear. So that here again there appears to be a similarity of response under the influence of a dissimilar emotion. The presence of another male or of an individual of another species may cause a general relaxing of the feathers and a spreading of wings on the part of the male, and this attitude sometimes appears to be the prelude to an attack, but the emotion, whatever it may be, disappears upon the retreat of the intruder. Why should the presence of an individual of another species influence the behaviour of the male? We shall find this question difficult to answer. The passing of a stranger through his territory may possibly evoke different emotions at different times and yet produce similar motor reactions. This is just the difficulty. There is the playful tendency, so common in the higher animals, which might be readily awakened by a harmless intruder of another species. On the other hand, the question of territory may here also dominate the situation and the intrusion may be genuinely resented. Who can say with any degree of certainty in which direction we are to look for the real factor? And with this first step undetermined, what useful purpose can be served by attempting to locate the true emotion? Attention may nevertheless be called to this one point; the attitudes affected by the male upon the intrusion of an individual of another species are similar in all respects to those caused by resentment at the approach of another male of the same species.
In one instance that came under my notice a male Sedge Warbler took possession of the same territory as a Marsh Warbler; and, further, made use of the same willow tree as his headquarters. This tree was situated only a few yards
40
