MARSH WARBLER 



next we must, I think, assume that this is the case, and that 

 each individual acquires the imitations during its lifetime. 

 An interesting experiment might be made with young Marsh 

 Warblers if they could be successfully reared in confinement. 



It is difficult to understand what part, if any, imitation 

 in the limited sense in which we are here discussing it can 

 play in furthering the life of the individual. The only explana- 

 tion we have is that these modifications of the song evoke in 

 different degrees the pairing impulse of the female, but even 

 when we interpret this in a very broad sense it is not altogether 

 easy to reconcile it with the facts we have at our command. If 

 these diverse modifications of song have differential effects, 

 such effects must be due to the quality, quantity, or both, of 

 the imitations. Those individuals, in brief, which start life 

 with an instrument capable of more perfect reproductions will 

 acquire a greater number of imitations and consequently be 

 more likely to secure mates. But we can scarcely assume 

 that imitations, however perfect they may be, will arouse the 

 pairing instinct of the female in a greater degree than the 

 true song ; and so the development of the imitative faculty 

 must run parallel with the development of the vocal powers 

 in other directions, the one supplementing the other from the 

 point of view of this theory. Now since the acquirement of 

 imitations is a matter of experience, and since observation 

 shows that some imitations are susceptible of revival, the 

 older birds will have predominant opportunities of securing 

 mates, the younger, no matter how well they may be endowed 

 congenitally, being at a disadvantage in competition with 

 their more experienced rivals. This factor of experience then 

 will to some extent neutralise the beneficial effects arising 

 from the possession of a slightly more perfect instrument, 

 though perhaps not altogether so, for it may be argued that 

 over a long period of time those individuals which were not 

 so perfectly endowed would on the average be at a disadvan- 

 tage ; the point however is a debatable one. Another 

 difficulty arises from the peculiar similarity in the strains 



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