1 36 E VOL UTION OF BIRD- SONG 



wrens have been inherited from common ancestors 

 respectively, the identity of tones just mentioned 

 indicates the accuracy of the operation of heredity, 

 or of fiHal mimicry ; but, though we know that many 

 analogous cries are often inherited, it does not follow 

 that the persistence of particular tones is wholly due 

 to the same influence. It is conceivable that the 

 influence which first occasioned particular modula- 

 tions has continually operated in their perpetuation. 

 We hear comparatively so few of the noises which 

 a bird hears in a feral life, that we cannot tell 

 whether the sounds it produces resemble those to 

 which it is most accustomed. 



The family resemblances between the notes of 

 allied birds must be due to heredity or to mimicry. 

 It is evident that the notes of several species are 

 perpetuated through many generations solely by 

 inheritance ; but the wide range of certain tones 

 aflbrds ground for the view that the persistence of 

 characteristic cries in widely separate localities may 

 be due to the influence of some equally persistent 

 originals, towards which they have been modified by 

 mimicry. Certain it is that even human ears can 

 perceive resemblances between certain cries of birds, 

 and other sounds frequent in the birds' habitats. 

 This subject will be discussed in relation to imita- 



