SUBJECTIVE LESSONS. 81 



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

 theory is here advanced to account for the origin of bird 

 migration ? What other animals migrate ? What do 

 most animals seek 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 chief function ? Mention several types of bird music. 

 To what does the song season correspond ? When and by 

 what species is it inaugurated ? When is it practically 

 concluded ? Is there a second song period ? What birds 

 first cease singing ? What birds are midsummer 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 (Chapter 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). What 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- 

 yerament shown in nesting ? Mention several kinds of 

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



