Page:The British Warblers A History with Problems of Their Lives - 8 of 9.djvu/17

 quickly in their wake that it is seldom we find two or three adjoining territories occupied by single individuals; a female is generally present in one of them, and her presence seems to stimulate the sexual instinct of all the males in the immediate vicinity, and to render the corresponding emotion of pugnacity proportionately active. It is, moreover, by no means easy to discover the female when the foliage is well advanced, a fact which adds to the difficulty of obtaining reliable information. I have, however, noticed some males fighting early in the season when there was no reason to suspect the presence of a female. Quarrels become of frequent occurrence when a fair proportion of the males have arrived and taken possession of adjoining territories, and such quarrels are more frequent on the boundaries than in the centre of a territory. Since the migration of the females is spread over some considerable time, it often happens that one of two males with territories adjoining obtains a female some few days before his neighbour, and this results in much disturbance. The female wanders about the territory in which she has settled, but does not confine herself so strictly to the limits as her mate; when therefore she intrudes upon a neighbouring preserve and is followed by her mate, considerable excitement ensues. The male, whose territory is invaded, flies towards the intruder, spreads his tail, raises the feathers of his body, and gives vent to his feelings by uttering his song or harsh alarm note, which is sometimes sufficient to make the intruder beat a retreat, but if it does not do so, the disturbance is liable to be continued, and the excitement may even become so acute as to cause a commotion in the bird life of the surrounding district. The owner then follows the intruder, and conflicts occur in which there is much fluttering of wings and snapping of bills. One of the most interesting features of the accompanying behaviour is the passionate utterance of the song. The usual song of the species is an even flowing warble, but on occasions such as I am describing it is more suffused with feeling tone, and may even deteriorate into