298 



THE VERTEBRATE ANIMALS 



attached to the wings, aid in locomotion, while the wing itself, a 

 modified arm, is one of the most evident adaptations to life in the 

 air. 



Flight. — Watch a bird in flight. The tip of the wing usually 

 describes a curve which results in the forming of the figure 8. 

 The rate of movement of the wing differs greatly in different birds. 



The wing of a bird is slightly concave 

 on the lower surface when outstretched. 

 Thus on the downward stroke of the 

 wing more resistance is offered to the 

 air. Birds with long, thin wings, as 

 the hawks and gulls, move the wing 

 in flight with much less rapidity than 

 those with short, wide wings, as the 

 grouse or quail. The latter birds start 

 with much less apparent effort than 

 the birds with longer wings ; they are, 

 however, less capable of sustained 

 flight. 



Feathers. — Few people realize that 

 the body of a bird is not completely 

 covered with feathers. Featherless 

 areas can be found on the body of 

 any common bird, although tiny " pin 

 feathers " are found on such areas as 

 well as on other parts of the body. 

 Soft down feathers cover the body, 

 serving for bodily warmth. Larger 

 feathers give the rounded contour to 

 the body. In the wings we find quill 

 feathers ; these are adapted for service 

 in flight by having a long hollow shaft, 

 from which lateral interlocking 

 branches are given off, the whole 

 making a light structure offering considerable resistance to the 

 air. Feathers are developed from the outer layer of the skin, and 

 are formed in almost exactly the same manner as are the scales 

 of a fish or a lizard. The first feathers developed on the body 



Feathers of a meadow lark. 

 '\\'hich of the above are used 

 for flight ? How do you know ? 

 From photograph loaned by 

 the American Museum of Nat- 

 ural History. 



