THE ENGLISH SFAjRl;()n' 3(1 



port of New York the incoming of huntlrecLs of immigrants 

 allured l^y the prospects of freedom from military service, 

 excessive taxation, and oppression in various forms. To-day, 

 with improved facilities for travelling across continents and 

 oceans, the human tide moves back and forth more freely than 

 ever before. 



In temperate climates the change of seasons leads certain 

 animals to migrate towards the equator during the winter and 

 to return towards the poles in summer. It has been suggested 

 that the animals were first driven soutliward l)}' the glacier, a 

 vast ice-cap that reached in North America from the pole south- 

 ward to a line extending from New York City to southern Ohio, 

 thence to near Chicago and on, south westward, over the Great 

 Plains to the Rocky Mountain region. When the glacier re- 

 treated northward again, the animals that had been forced 

 south made their way l)ack to the homes of their ancestors. 

 But many of them retm-ned to the south again on the ap- 

 proach of each winter's cold. For example, the Bison, which 

 formerly lived in countless thousands on the Great Plains, 

 migrated south with the sun, and thus kejit in verdant pas- 

 tures, and similarly to-day scores of species of birds migrate 

 in the spring and autumn. 



The Migration of Birds. — In respect to their migratory 

 habits all birds are divided into four classes. The examples 

 that follow are all taken from the latitude of New York City 

 and Chicago. 



1. Residents. These do not migrate, or migrate so short a 

 distance that those individuals that nest in the northern part 

 of the range do not move below the southern limit of the 

 summer range of the species. Examples : the blue jay and 

 song sparrow. 



