GENERAL SUMMARY AND CONCLUDING REMARKS
had a double effect; it would not only have fostered the, survival of congenital variation of behaviour in the direction of removal, but also the congenital variation in the direction of an efficient covering which would contribute towards ease of removal.
Some discussion of the vocal powers will be found in the histories of the Willow Warbler, Blackcap, Lesser Whitethroat and Marsh Warbler, more especially with regard to the utility of song, the power of imitation, the variation in different districts, and so forth; and now when one comes to gather up the threads, the mystery of it all deepens and hope of interpretation wanes. For what is the use of song? To evoke the pairing hunger of the female as Prof. Lloyd Morgan suggests? It may be so, yet the facts at our disposal are not of the kind to carry conviction. The same considerations which led to our questioning the correctness of Professor Groos' theory in regard to emotional manifestation are relevant here also. I made a suggestion in the life of the Willow Warbler and discussed it again in that of the Marsh Warbler. Briefly it was as follows: a male must have some means of proclaiming to the females the fact that it is in possession of a territory and ready to reproduce, and this it can accomplish through the medium of those special sounds emitted at this particular season. Such sounds are therefore not only directly related to but are an integral part of the law of territory; and since on the average it will be the more vigorous males that will secure territory and attain to reproduction a gradual augmentation in the power of producing sounds ought to follow. The facts which were used in support of this view will be found principally in the life of the Willow Warbler. It must not, however, be supposed that this suggestion explains, or attempts to explain, why a Land-Rail, for instance, should produce such raucous sounds and a Marsh Warbler such beautiful ones; it does not touch the question of the origin of the sound nor claim to show why this or that voice should have been framed in just this or that particular fashion; but
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