INTRODUCTION 



stated in Chapter II., on " Alarm -notes," and 

 Chapter IV., on " Call-notes." 



Between these chapters will be found one treat- 

 ing of the influence of combat. This feature is 

 difficult to discuss with anything like precision : 

 incidents have been adduced tending to show that 

 the pugnacious instinct has some influence on the 

 use of the voice. 



I soon found that young birds acquire first the 

 call - cries and alarm - notes of their respective 

 species ; that in each species these notes are much 

 less liable to vary than are the songs ; and that in 

 different species physically allied, they are more 

 alike than are the songs of those species. Another 

 most interesting feature, and one which I commend 

 to the attention of ornithologists everywhere, was 

 the prominent occurrence of a particular cry in one 

 species ; its occurrence in a less marked form in 

 some one or two allied birds, in which another cry 

 might be the most pronounced ; and the utterance 

 of this second cry by some other allied birds, which 

 had not the first-mentioned note. I could trace 

 this to some extent in the thrushes, but more especi- 

 ally in the finches. These facts will be appreciated by 

 naturalists, as bearing on the question of a common 

 ancestry of species. For purposes of suggestion I 



