GARDEN WARBLER
outlines become indistinct, and by a rapid sidelong motion of the legs slides gracefully in the direction of the female, uttering a quiet call-note meanwhile. Yet this manifestation, surprising as it is, is not without a parallel in the lives of other species, for both the House Sparrow and Blackbird flutter their wings similarly at a corresponding period, and the Pied Wagtail not only flutters its wings, but, with a similarly rapid motion of its legs, seems to glide this way and that around the female.
After the arrival of a female in a territory, the owner is usually to be found in close proximity to her. Not always, however, for at one moment she wanders outside his accustomed circle and at another he deserts her for a short space of time. But, as a rule, they can be seen together, and their companionship becomes more intimate after the actual construction of the nest has commenced. The three principal factors which evoke emotional response in the male during the period of sexual activity are as follows: the presence of a second male, the presence of an individual of either sex of another species, and the sexual instinct. The first two of these we will discuss later; the third, the sexual instinct, is doubtless indirectly responsible for the first two, but for the moment we will confine ourselves to the manifestations of it when the pairing situation is not complicated by the presence of a third individual. Maximum activity is reached during or just prior to the actual discharge of the sexual function. A partial expansion and slight quivering of the wings and a partial spreading of the tail on the part of the male can frequently be seen, and often occurs when he is above the female, high up perhaps in some tree while she is in the bushes beneath, and is usually the prelude to a pursuit of or a sporting with her. Or, instead of flying directly to her, he may float slowly downwards on outspread wings, singing as he flies. The rapid fluttering of the wings already referred to is the most striking manifestation, and the intensity of this action varies at different times but reaches its maximum
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