GENEEAL SUMMARY AND CONCLUDING REMARKS 



congenital factor. What then is the meaning of the evidence 

 derived from birds in captivity ? An answer to this question 

 may perhaps be found in the power of imitation so highly 

 developed in many species. This remarkable power is referred 

 to in the lives of the Blackcap and Eeed Warbler, more fully 

 in that of the Marsh Warbler, and some idea of the nature 

 and extent of the development can be gained by studying the 

 lists of voices and songs imitated. It is apparently so simple 

 a matter for certain species to reproduce alien strains that one 

 may well ask how a definite type could have been evolved 

 in the absence of any instinctive basis. I should not demur 

 to song being spoken of as a matter of imitation, though 

 founded on an instinctive basis, if by this is meant that a 

 stimulus of an appropriate kind is necessary to set it agoing, 

 but we should not be then justified in speaking of song as 

 having been learnt by imitation. The power of imitation and 

 the true song must be two separate manifestations of one 

 process • may not the absence of the true song in the case of 

 birds reared in captivity be due to an absence of the ap- 

 propriate stimulus, just as in the absence of appropriate 

 stimuli other hereditary co-ordinations refuse to respond, the 

 alien cries being the stimulus to the power of imitation which 

 must also be founded on a congenital basis. 



The more one reflects upon this problem of vocal imita- 

 tion the more difficult it becomes to estimate its true value 

 from the biological standpoint. Dr. Thorndike regards the 

 phenomena presented by imitative birds as a specialization 

 removed from the general course of mental development. 

 Others think that it has a special part to play in the sexual 

 process, and while dissenting from this view — my reasons for 

 doing so will be found in the discussion of the subject in the 

 life of the Marsh Warbler — I should be the first to admit the 

 incompleteness of our knowledge in regard to the whole 

 matter. 



The variation in different districts is referred to in the 

 history of the Lesser Whitethroat, and the suggestion is there 



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