144 



BIRDS 



the Northern United 

 States and passes the 

 winter in South Amer- 

 ica, migrating a distance 

 of over five thousand 

 miles. In the case of 

 the robin the migration 

 is limited to a short 

 flight to the south to 

 some protected swamp 

 provided with water and 

 food. A probable cause 

 of migration is the fail- 

 ure of food supply as 

 cold weather comes on 

 in the fall. 



138. Economic Impor- 

 tance of Birds. — The 

 chief food of birds is 



insects, such as plant lice, larvae of beetles, butterflies, 



moths, borers, etc. The chickadee, for example, feeds 



on plant lice as well as 



other foods ; the downy 



woodpecker feeds on 



codling moths and 



borers ; the nuthatches 



and brown creepers feed 



on insects and insect 



eggs that are hidden in 



crevices and under loose 



pieces of bark. Other 



useful birds are the song 



sparrow, chipping spar- 



Figure 148. — Chimney Swift and Nest. 

 Part of the birds have been crowded out. 



row, robin, bluebird, 



Figure 149. — Junco. 



A transient bird nesting in Canada, and 

 on the high hills and mountains of 

 the Northern states. 



