1 90 E VOL U TION OF BIRD-SONG 



grass a regular hiss is thus caused. It appears 

 that serpents which live among rocks do not hiss 

 so volubly as those of grassy places. 



Resemblances to Sounds uttered by Birds 



There are more resemblances between the cries 

 of birds than between those of birds and other 

 animals ; and this seems only natural. But here 

 also we find abundant traces of voluntary mimicry, 

 so that we can hardly say certainly whether an 

 individual bird is intentionally reproducing the 

 notes of another, or is repeating the mimicry of 

 some ancestor, descended to him by the agency of 

 filial imitation. It is very possible that birds of 

 different genera, living together, may learn cries 

 from each other. The golden-crested wren, for 

 example, has a call-note which resembles that of 

 the tree-creeper (as Yarrell observed, op, cit. vol. iv. 

 p. 470) ; and these two species are often together. 

 The nuthatch often repeats as a call-note a slight 

 squeak like that of the creeper and goldcrest, and 

 also closely like that common to the coal, blue, and 

 great titmice. In fact, all of these birds, so fre- 

 quently associated, utter this call. The nuthatch 

 evidently possesses some power of mimicry, for I 



