BRITISH WARBLERS 



imitated of which we have been speaking, and which cannot 

 well supply the conditions necessary to produce differential 

 effects upon the female. For, however broadly we interpret 

 this view, however confidently we assert that imitations, 

 broadly speaking, create a more effective pairing situation, 

 yet inasmuch as of two individuals it will always be the one 

 that has acquired more numerous or more perfect imitations 

 which will attain to reproduction, there must result a constant 

 tendency towards variation which can scarcely make for the 

 similarity that we observe. If we had sufficient knowledge 

 of the vocal powers of those species in which the faculty 

 was highly developed, we might possibly find that it always 

 followed certain definite lines, that it was, so to speak, the 

 outcome of a certain type of vocal development. A song, 

 for instance, in which articulation is conspicuous and the 

 utterances distinct may lend itself more readily to imita- 

 tion than one in which the flow of phrases is more con- 

 tinuous. If this were really the case, the tendency to imitate 

 song need not necessarily be of service to the individual, 

 but only the result of a definite type of instrument, and 

 on this view the similarity referred to would become more 

 intelligible. But evidence on many points is still needed. 

 We require information concerning the behaviour of the males 

 in their winter home. Do they there sing and copy indigenous 

 species ? We need information concerning the course of and 

 the time occupied in the migratory journey, and definite 

 knowledge as to whether each individual male, upon arrival 

 at its breeding home, introduces imitations into its song, and 

 to what extent variation occurs in the quality and quantity 

 of such imitations. There is room for much observation 

 here. 



Of the call notes it is necessary to say but little. The 

 most common one is not an unmusical sound, and is similar in 

 some respects to the corresponding note of both the Eeed and 

 Sedge Warblers, but rather more distinctive than either of these. 

 It is uttered at various times and by both sexes, and can be 



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