THE EVOLUTION OF BIRD-SONG. 241 



It is to be observed that, besides leisure, meditation is 

 necessary to song, and that lethargy militates against the 

 development of the voice. Birds whose food is precarious 

 (e. g. the Raptores and Colymbiclce) are generally either hungry or 

 gorged, and consequently vigilant or lethargic ; hence they have 

 but little inclination to vocal exercise. It is probable that 

 characteristic peculiarities of movement during song (such as 

 flight, which seems to be, then, an exaggeration of the fluttering 

 of the wings that is frequently a call- action in young, and some- 

 times in adult birds) have been developed contemporaneously 

 with variations in the voice. 



Certain birds (e. g. the Kedbreast, Wren, Accentor, Blackbird, 

 and Blackcap) imitated mellow tones, and intervals of pitch, rather 

 than other characters of sounds ; and the music thus reproduced 

 might have been heard in the murmurs of streams, or in other 

 naturally or artificially produced noises. It also appears that 

 intervals of pitch in human music are sometimes imitated and 

 clearly reproduced by birds. I have recorded a great number of 

 such instances. At Stroud the Thrushes often utter a phrase 

 which I have heard for nearly twenty years whistled, as a 

 call, by the boys of that neighbourhood. At Frocester, in 

 Gloucestershire, near the church, I have heard at least two 

 Blackbirds and two Thrushes sing, fairly correctly, two distinct 

 musical phrases. In the construction of arbitrary phrases 

 combativeness may have had some influence, for certain parts 

 of the songs of the Greenfinch, Goldfinch, and Starling are 

 never sung to the female, but are uttered defiantly. The 

 same ardour which has induced the development of the 

 arbitrary phrase has caused its variation. In this, as in the 

 production of many arbitrary phrases, variation has been guided 

 by imitation ; but not invariably so, for some individual birds 

 (e.g. Greenfinches, Chaffinches, and Wrens) vary the pitch and the 

 number and quality of the "character-sounds" in their phrases 

 in a way that suggests no attempt at mimicry. On the other hand, 

 certain birds (e. g. the Blackbird, Missel Thrush, and Kedstart) 

 continue their songs, after the utterance of ordinary or arbitrary 

 phrases, in imitations. The Blackcap often sings in this way, but is 

 noticeable as sometimes preluding its mellow phrases with softer 

 imitations. 



Many birds reproduce in song the notes of others. So far as 



