32 ] How to Understand the Bird* 



flaps as a unit, producing speed and lift at the same time. During 

 the upstroke, the wing is folded. 



When a bird glides, it loses altitude to keep its forward-pushing 

 motion. In static soaring, the bird takes advantage of up-air cur- 

 rents which offset the loss of altitude suffered during its gliding 

 flight. For dynamic soaring a bird such as the albatross will use 

 the force of the wind. Wind force increases with altitude; hence 

 the bird, after descending most of the way, levels off with the 

 slowing down of the wind near the surface of the water, and then 

 ascends again, once more making use of the air currents. 



Birds use their wings differently depending on the kind of 

 flight, such as horizontal, soaring, descending, gliding, hovering, 

 taking off, and climbing. Various types of birds have wings of 

 different shapes and proportions, and each employs each wing in 

 the distinctive manner appropriate to it. 



An important feature of the bird's flying mechanism is a sinew 

 with elastic qualities. On the downward thrust of the wing, the 

 sinew holds the feathers in a tight overlapping position. When 

 the wing comes up, the tension of the sinew relaxes and 

 feathers part and rotate. This allows air to flow between 

 as an aid in flight. 



It gives us pleasure to understand how birds fly, but all the 

 analysis in the world cannot dim the initial thrill of seeing birds 

 in flight. 



The Mystery of Migration 



There is no more fascinating way of arousing interest in flight 

 than having your child catch a sight of migrating birds perhaps 

 a flight of geese in military formation, or a close-massed flock of 

 grackles racing like a dark wind-blown cloud. Even after years of 

 research and experiment, scientists speak of the "mystery" of bird 

 migration, for they still do not completely understand it. Yet, 

 puzzling as this semiannual pilgrimage of countless birds is, it is 

 no more puzzling to me than the way in which my daughter took 

 note of it before she reached her second birthday. On three differ- 

 ent occasions we were having a late afternoon walk along streets 



