GENERAL SUMMARY AND CONCLUDING REMARKS 



had a double effect ; it would not only have fostered the, 

 survival of congenital variation of behaviour in the direc- 

 tion 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 White- 

 throat 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 considera- 

 tions which led to our questioning the correctness of Professor 

 G-roos' 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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