THE THRUSH GENUS 393 



number of nestlings that survive to breed is comparatively very small, 

 and the yearly addition to the parent stock is balanced before the 

 winter is over by the loss caused through the ravages of cold and 

 hunger referred to earlier in the chapter. How great the annual 

 mortality is may easily be realised from the fact that the number of 

 individuals within each species remains more or less the same in spite 

 of the great quantity of eggs that are laid, a fact which is not, of 

 course peculiar to the genus Turdus. 



VI 



It is left for me now to describe the various call- and other 

 notes of the Thrushes. This can only be imperfectly done, for very 

 little attention has been paid to the subject, though there is no 

 doubt that a careful comparison of the notes uttered by the various 

 species in the genus would prove not only a valuable contribution to 

 the study of its evolution, but would throw no small light on the 

 origin, meaning, and development of bird language. My own 

 observations are limited to the blackbird and song-thrush. 



What strikes one in studying the notes of birds is that they 

 appear to be differentiated rather according to the relative intensity 

 of emotion they express than the function they perform. This is well 

 illustrated by those of the blackbird and song-thrush. They have 

 each two common notes. Both utter a sound that may be syllabled 

 as tchuck !, and the second note of the thrush ptick ! (the p scarcely 

 sounded) corresponds to the familiar mink! of the blackbird. It 

 probably requires a fine ear to distinguish much difference between 

 the tchuck! of the two species, but with a little practice it is quite 

 easy to utilise the second notes as a means of identification. Both 

 notes, the tchuck ! and the ptick ! or mink ! are used to express alarm, 

 very often on the same occasion, but the more intense the alarm of 

 the bird, the more frequently and more rapid become the pticks ! or 

 minks!, till in moments of extreme excitement these notes are 



3E 



