LEARNING BIRD LANGUAGE 203 



fied to a scream of rage, is the battle cry of the 

 birds, and comes when they attack a rival, a crow 

 around a nest, a cat, a squirrel, or a human being. 



The same cry, in greater agony and prolonged, 

 comes when a bird is wounded, caught in a trap or 

 by a cat, or when its young are being taken from 

 the nest by strangers. This cry is commonly de- 

 scribed as a "squall" or "squawk." 



A large number of songbirds have one song of 

 greater or less length, which is sung in differing 

 ways in different circumstances. Of course, the 

 imitators such as catbirds, brown thrashers, and 

 mocking birds change their song in imitation of 

 whatever sounds they hear while singing or remem- 

 ber from former songs. But most of the others 

 sing a succession of notes in individual ways, while 

 some improvise as they sing, like the bobolink. 



In the early spring, after the disbanding of 

 families for the season, and through the winter, 

 the song of the birds is one of joyful abandon. 

 When they are full-fed, free, content, the music 

 bubbles from their throats in a swelling chorus. 

 Sometimes they sing their notes at the highest 

 pitch they can reach, then in middle tone, and 

 then with scarcely parted beak they warble them 

 over in a greatly distended throat, diminishing to 

 a mere whisper of sound, which they sometimes 

 continue for the full length of their strain. The 

 black-headed grosbeak is probably master of this 

 art, but in much experience in study of the songs 



