EFFECT OF ENVIRONMENT 179 



The detection of the imitations sung by birds in 

 cages is rendered easy by the circumstance that the 

 birds almost necessarily reproduce sounds heard 

 around the cages, and hence familiar to persons in 

 charge of the captives. Conversely, the imitative- 

 ness of wild birds would be difficult of detection 

 by any one not familiar with the subjects imitated, 

 whether these were cries of birds or sounds caused 

 by other animals. I shall endeavour in subsequent 

 pages to show how greatly imitative are many of 

 our own wild birds, especially the sedge -warbler, 

 starling, thrush, blackcap, robin, and skylark. Until 

 extensive experiments have been made, we shall not 

 be able to determine the extent to which imitation 

 generally affects the call-notes of the young. We 

 know that it is responsible for the character-cries of 

 the goldfinch and brown linnet ; and probably it is 

 equally powerful in several species allied to them. 

 However this may be, we are sure that songs are 

 often completely ordered by this faculty, and if songs 

 are thus influenced, call -notes also probably are 

 similarly affected. Our present knowledge merely 

 shows that the characters of the call-notes are more 

 permanent than those of the songs, and that they are 

 more influenced by physical inheritance or by filial 

 mimicry. The call-notes, from being less variable 



