THE BIRDS 



201 



where many are killed by flying against the walls. In 

 most cases, however, a bird's memory for a route it has 

 once followed is far better than that of the average human 

 being. 



The tendency to migrate is doubtless instinctive, but 

 the particular route followed is mainly a matter of experi- 

 ence and tradition. Birds commonly migrate in flocks, 

 and it is probable that it is the older and more experienced 

 birds that lead the way. While it may seem curious that 



FIG. 155. Red winged blackbird. 



birds should leave a genial clime and fly thousands of 

 miles to the cold and barren regions of the Arctic Circle 

 to rear their young, it must be borne in mind that this 

 northern region is one in which during the short summers 

 that occur, there is an abundance of food in the form of 

 berries and insects (especially mosquito larvae) and com- 

 paratively few enemies to molest the young. The migra- 

 tion of birds affords a means of taking advantage of these 



