442 



THE EMPIRE OF THE AIR. 



It soars well, but only wlieu at leisure. It weighs 1.32 pounds, and 

 its surface amounts to 1.72 square feet, being in the proj)ortion of 1.3 

 square feet to the pound. 



Fig. 



-Kestrel Falcon. 



Eagles. — With the fish-hawk {Pandion fltiinalis) we reach the heavy 

 birds. We still find a bird which beats the air, but already the le- 

 sults of inertia are manifest. When the mass is 2 pounds or more there 

 appears a steadiness in flight not found among the 1-pound birds. 



Fig 8.— rcrcgiine Fakon. 



The small eagles of Europe and of Africa, the imperial eagle with white 

 back (AfjniJa heJiaca), and the great golden e;igle {Aqirila chri/.sai-f(() 

 found in the Alps, all liave the same modes of flight. Their talents 

 as sailing birds increase with their weight. 



Tlie necessities of their existence require many different qualities : 

 First, they must be able to remain easily in the air, in order to survey 

 the field, to watch a possible prey for whole hours; therefore they 

 must be able to soar well, and this they do to perfection. Once the 

 prey discovered, there needs be great speed to capture it, for often it is 

 a duck, and a duck flies very fast; or it is a hare to be caught on the 

 run, and this is not at all an easy enterprise. To gain this great speed 

 the eagle utilizes gravity; he lets himself drop 200 or 300 yards, and 

 employs the velocity so acquired with great dexterity to catch the 

 game. These violent hunting exerticms in catching other rapid animals 

 require an enormous muscular power on the part of these birds. 



