VI On the Songs of Birds 155 



leading principle, one might say, of a bird's mind, — 

 the Marsh Warbler is the radical in the genus Acro- 

 cephalus, with an irresistible desire to push into fresh 

 experiments and innovations in song, and to appro- 

 priate freely the gifts and inventions of his neigh- 

 bours. Or, in sober language, the nervous intensity 

 of some birds is certainly greater than in others ; and 

 these are often the most vivacious singers. If they 

 have developed no very definite form of song for 

 themselves, it may be that their excitability leads 

 them to imitate others. And as it is really from the 

 mental constitution of our own species that we can 

 learn most about that of animals, it may not be out 

 of place to remark that it is exactly the brightest, 

 quickest, most fun-loving among human beings who 

 are most prone to imitation and caricature. 



While I am on this subject of mimicry in song, it 

 may not be amiss to advert for a moment to a theory 

 lately propounded in the Zoologist,^ which would ex- 

 plain all songs as imitations, either of the utterances 

 of other birds, or of inarticulate sounds which are 

 constantly obtruded on the bird's ear. The writer of 

 these articles has made a most painstaking analysis 

 of many of the best-known songs ; his perseverance 

 is admirable, and it is only in his conclusions that he 

 seems to have let his fancy run away with him. He 

 suggests, for example, that the Song-thrush began 

 1 For 1890, pp. 233 foil 



