SUBJECTIVE LESSONS. 81 



Origin of Migratioyi (Chapter IV, pages 58-61). — What 

 theory is here advanced to account for the origin of bird 

 migration? Wliat other animals migrate? What do 

 most animals seelc during the period of reproduction ? 

 Give illustrations. Describe the migrations of certain sea 

 birds. What has been the probable influence of the gla- 

 cial period on bird migration ? Describe the route followed 

 by Bobolinks when migrating. What does this illustrate? 

 In what manner does the migration of birds resemble the 

 flight of the Carrier Pigeon ? 



The Voice of Birds. 



Song (Chapter V, page 62). — What is song? What is 

 its cliief function ? Mention several types of bird music. 

 To what does the song season correspond ? When and b}' 

 what species is it inaugurated ? When is it practically 

 concluded ? Is there a second song period ? What birds 

 first cease singing ? What birds are midsummei* singers ? 



Call-notes (Chapter V, page 65). — What is the relation 

 of call-notes to song ? What do the calls of the Robin 

 express ? Do birds inherit the calls and songs ? Do they 

 ever acquire the notes of other species ? 



The Nesting Season. 



Time of Nesting {Q\\a,^iQv VI, page 64). — At what season 

 do migratory birds nest ? When do tropical birds nest ? 

 Why are birds obliged to nest at a certain season ? Give 

 some examples illustrating the relation between nesting 

 time and food. 



Mating (Chapter VI, page 65). — (See page 45, Synopsis 

 of the Secondary Sexual Characters of Birds.) 



The Nest (Chapter VI, pages 65-68).— Wliat is the first 

 step in nest-building ? Mention several sites in which birds 

 may nest. What is the chief desideratum ? Why can sea 

 birds often lay their eggs in exposed places ? How is tem- 

 perament shown in nesting ? Mention several kinds of 

 material used by birds in nest-building. How have birds 



