10 BIRD FRIENDS 



way in a fog when landmarks are invisible, or over 

 large bodies of water where no landmarks can be 

 seen; and frequently birds fly so close to the ground 

 or water that they cannot see any landmarks. And 

 again birds may travel straight for long distances 

 over routes which they have never seen before. 



Sense of direction. Still another suggestion is 

 that birds have a sense of direction which enables 

 them to find their way. This is simply ascribing a 

 power to birds without any real explanation, but 

 experiments which have been made with birds seem 

 to show quite conclusively that some birds do pos- 

 sess this sense of direction. Several birds were cap- 

 tured on Bird Key south of Florida, and were placed 

 in the hold of a steamship and taken north to Cape 

 Hatteras, a distance of about one thousand miles 

 from their nesting-sites, and released. Five days 

 later, two of them were back on their nests. In this 

 case no other explanation seems possible than that 

 the birds found their way through a sense of direc- 

 tion, as the birds had never flown over this route 

 before, and could not see the way over which they 

 had come, and so could not make use of any land- 

 marks. 



Causes of migration. The most puzzling of all 

 questions concerning migration is, why do birds 

 migrate? At the outset it may be stated that bird 

 students are not agreed as to the causes of migra- 

 tion, but brief reference may be made to a few of the 



