How to Understand the Birds [31 



the air, arms outstretched, and a faint hope that he too can "take 

 off." 



BIRDS ARE BUILT FOR FLIGHT* 



It helps your inquisitive child to understand the mechanics 

 of flight if you point out that the bird's streamlined form is of 

 great advantage in flying. Besides this, it has an extremely light 

 structure: Its bones and the shafts of its feathers are hollow and, 

 as is easily seen, the size of its wing is greater in proportion to 

 its body than an arm is to the human body. 



You can then go on to compare the child's framework to the 

 bone and feather structure of the bird, which has a bone corres- 

 ponding to his upper arm and another to the bone between his 

 elbow and wrist. Have the child extend his thumb upward, hold 

 his first and second fingers in a horizontal position, and fold the 

 other two into his palm somewhat as he would do in making a 

 pretend-gun out of his hand. This will give him a rough com- 

 parison with the structure of a bird's wing. 



The bird has a winglet corresponding to the child's thumb, 

 and a second and third digit similar to his extended fingers. 

 These are sometimes extended upright, but may also be held 

 horizontally. While the child's arm, hand, and fingers are covered 

 only with skin, the bird has flight feathers also one sheath on 

 the "forearm," and another series on the "hand." The number 

 of feathers varies in different birds. 



FLIGHT TECHNIQUES 



There are four types of bird flight: flapping, gliding, static 

 soaring, and dynamic soaring. In flapping flight the "arm" wings 

 help to lift most large wings into the air, while the "hand" wings 

 produce propulsion through the air. Speed or forward motion is 

 gained with each downward stroke of the wings; lift is obtained 

 on up-and-down strokes. In this up-and-down motion the wing 

 tips move through a much greater arc than the wrists would. 

 (In airplane flight lift and speed are produced by the propeller 

 and the wings.) In small birds, such as the finch, the whole wing 



