BRITISH WARBLERS
One more question may be raised with regard to emotional behaviour. Does every individual of a species respond similarly under similar circumstances throughout the whole of its breeding range? Beyond the fact that I have never seen Marsh Warblers in this country expand their wings so fully as those in Holland, I have no evidence bearing upon this point. Yet more wonderful facts are to be found in nature than a variation in the intensity of the reactions in different geographical races; for only if the reactions have a use, and if that use bears some direct relation to the particular degree in which they are executed, should we expect to find them oscillating round a common mean.
Closely connected with, but a separate aspect of this emotional behaviour is the peculiar habit, common to the males of certain species, of picking up and carrying decayed vegetation of some description whilst they are following the female during sexual emotion. We may regard this habit as a stepping-stone to the next important stage in the period of reproduction, the building of the nest. A reference to the plates in the lives of the Grasshopper Warbler, Savi's Warbler, Lesser Whitethroat, and Blackcap will convey some idea of the appearance of the respective males during this peculiar performance. The habit may form part of the sexual life of most species, but whether it be so or not it is evident that the disposition to secure and carry something is much more strongly implanted in the males of some species than in those of others. One would be surprised to find a male Grasshopper Warbler or Savi's Warbler that failed, when the proper moment arrived, to search for, pick up, and carry a piece of vegetation of some description—a decayed leaf of the hazel, oak, bramble, &c, or of the common reed, as the case may be—and equally surprised to find a male Willow Warbler, Chiff-chaff or Wood Warbler that behaved in this way. Here again all attempts at interpretation are rendered difficult by the absence of anything universal. The male Whitethroat builds nests even before a female has arrived, and this,
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