Page:The British Warblers A History with Problems of Their Lives - 6 of 9.djvu/29

 have already mentioned that the habits of the Willow Warbler and those of the Chiff-chaff are so similar that it is well-nigh impossible to distinguish between them in actual life. This is true of their habits as a whole, but the expression of sexual emotion differs considerably, and it is possible to recognise the peculiar wing-flapping of the Willow Warbler at some distance. This wing-flapping is not confined to one sex only, but forms part, though a lesser part, of the sexual manifestation of the female. It can be seen to the best advantage—for the peculiarity is then more striking—when both sexes perform at the same moment, an occurrence by no means unusual. Settling a few feet apart, they face this way or that, often in opposite directions, and standing in an upright position on the branch, partially extend their wings, and flap them at a moderate speed. Whilst thus performing they carry their heads rather high, slightly expand their tail, and become so completely absorbed in their performances, which may last for fully half a minute, that they take little or no notice of one another. At this period during the first few hours of daylight the wing-flapping is of frequent occurrence on the part of one sex or the other; and when a number of territories adjoin and a female is present in each one of them, this curious but interesting behaviour can be observed with but little difficulty. Even when the female is not in his immediate presence, the male may be seized with sexual emotion and express it in this manner. In its details the performance varies but little, the wings are not always expanded to a similar extent, and the tail is sometimes slightly raised. Silence is often maintained, but may be replaced by a highly pitched twittering sound uttered in sympathy with the bodily movement. Although apparently so absorbed when performing alone, it is quite clear that the male is very much on the alert and knows the whereabouts of the female, for in the midst of his emotion he will dart off without hesitation towards her, when the usual fluttering of wings and rapid pursuit follow.