BRITISH WARBLERS
Lesser Whitethroat, which, though having a helpless appearance, does not exhibit so marked a sign of a disabled limb. And if we are thus far agreed, our next step is to enquire whether any distinction can be drawn between these activities as a whole, and those which characterise the behaviour of a bird at other periods of excitement.
Now I submit that this is an important point to decide, for it appears to me that the functional similarity is so marked as to warrant the belief that all the activities, occurring at different periods of excitement, can be referred to a common origin. If the movements of any of the more demonstrative species such as the Avocet, Reeve, or Kentish Plover, when their young are approached, are analysed, it will be found that all the curious ways in which the limbs and feathers are made use of, the flapping of the wings, spreading of the tail, raising of the back feathers, lying on the ground, &c, have their counterpart in the actions of various species during the period of sexual activity. Even the alternate expanding of the wings of the Kentish Plover, which at once arrests attention on account of the peculiar nature of the movement, is not confined solely to this period of excitement, the female Marsh Warbler (Acrocephalus palustris) behaving similarly during sexual excitation. No better instance of this striking similarity could, I think, be found than in the actions of the Reeve when her young are approached on the one hand, and those of the male Pied Wagtail during sexual excitation on the other. Both these birds, at the respective periods of excitement, raise the feathers on their backs, lower their heads, lower and spread their tails, and in a crouching attitude with drooping wings run about the ground. Anyone, in fact, who studies the Grasshopper Warbler, or Savi's Warbler, or any of the more demonstrative species, during the period of sexual activity, cannot fail to notice, whenever the excitement reaches a certain degree of intensity, how great a similarity the resultant activities bear to those which occur amongst many species during the period in which the parental instinct is uppermost.
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