THE SONG AND NOTES OF BIRDS. in 



imposing and powerful than it really is. Many 

 other defenceless birds utter loud harsh screams 

 and cries when their eggs or young are menaced, 

 for precisely similar reasons. 



Then \ve have to consider another very distinct 

 class of notes, namely, the various cries uttered by 

 birds during migration, which serve the vitally 

 important purpose of keeping the members of a 

 flock together, and of crying the route to the less 

 experienced travellers. Another class of notes, and 

 which must be placed in quite a different category, 

 is that which includes the many varied sounds 

 which serve as a means of recognition, not only 

 between the sexes, but amongst all the individuals 

 of a species. The more difficult this recognition 

 is, owing to the habits of various species, the more 

 startling, striking, or sonorous do the notes become. 

 Thus nocturnal birds almost invariably utter excep- 

 tionally loud and piercing or very peculiar notes, 

 which undoubtedly serve the useful purpose of 

 indicating the whereabouts of these birds to their 

 mates or to other individuals of the same species. 

 Witness the loud cries of the Owls, the shrill notes 

 of various Plovers and Waders, the harsh quack of 

 the Ducks, the screams of the Divers, the twanging 

 sounds of the Waterhen, the booming of the 



