SUBJECTIVE LESSONS. 81 
Origin of Migration (Chapter TV, pages 58-61).—W hat 
theory is here advanced to account for the origin of bird 
migration? What other avimals 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 BIrps. 
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 midsammer 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 NestTina 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- 
_ perament shown in nesting? Mention several kinds of 
material used by birds in nest-building. How have birds 
