BRITISH WARBLERS
required, as a study of the life of the two Whitethroats will reveal; for the male Lesser Whitethroat spreads out its wings and tail in presence of the female in the same way as the female when anxious about her progeny, and the behaviour of the female Whitethroat, when her nest is intruded upon, is identical with her behaviour sometimes when in the presence of the male. And it can by no means be said that, in either of these two cases, there is any difference, so far as the attitudes assumed are concerned, at one moment from that at another; in this respect only is any difference observable, that whereas at the period of sexual activity the flapping of the wings takes place while the bird is in the bushes, but not actually on, although frequently close to, the ground, at the period of parental care it occurs for the most part when the bird is actually on the ground. But assuredly the difference between a spreading and waving of the wings upon the ground, and a similar spreading and waving a few feet above it, can never be pointed to as one of sufficient importance to form the basis of an entirely novel explanation. These facts, taken from the lives of two species only, are clearly insufficient, where so large a number of species are involved, until supplemented by others of a similar nature; and although I attach considerable significance to them, yet it is not on them alone that my conclusions are based. Bather do I look to the absence of evidence in support of the simulation theory on the one hand, and the functional similarity on the other, as furnishing the more important considerations. For since the activities, occurring at different periods of excitement, resemble one another to so large an extent throughout bird life in general, it is probable a priori that they have but one common origin. Therefore, until considerations of an a posteriori kind are supplied, tending to show that there is some difference in kind between those which occur during the period in which the parental instinct is uppermost, and those which occur at other periods, making it virtually impossible that they can
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