144 EVOLUTION OF BIRD- SONG 



umbellus), which bird strikes his wings rapidly above 

 his back in order to produce this sound. In view 

 of the various movements of the wings, which so 

 generally occur when birds approach their mates, it 

 is questionable whether the " instrumental music ): 

 produced by these birds is not often an accidental 

 consequence of an action intended as an overture. 

 However, the domestic pigeon obviously strikes his 

 wings together in flight as a call to his fellows. 

 There is some evidence that bird -songs do not 

 change in general characteristics except by a very 

 slow process ; but other facts suggesting the con- 

 trary conclusion will be subsequently related. Pliny 

 wrote of the nightingale (Nat. Hist., bk. x. cap. 43 : 

 ed. Bostock and Riley) : " Its note, how long and 

 how well sustained ! And then, too, it is the only 

 bird the notes of which are modulated in accordance 

 with the strict rules of musical science (?). At one 

 moment, as it sustains its breath, it will prolong its 

 note, and then at another will vary it with different 

 inflections ; then again, it will break into distinct 

 chirrups, or pour forth an endless series of roulades. 

 That there may remain no doubt that there is a 

 certain degree of art in this performance, we may 

 here remark that every bird has a number of notes 

 peculiar to itself; for they do not all of them have 



