THE STRUCTURE AND ACTIVITIES OF BIRDS 347 



becomes a pliable but also resistant structure, which is 

 strong but light and admirably adapted for purposes of flight. 

 Beneath the large feathers are smaller down feathers which 

 have a slender stem and hookless barbs. The down feathers are 

 very effective in preventing the escape of the body heat. 



Fig. 226. — Red-tailed hawk about to sit on her eggs. The nest was in a 

 birch tree 40 feet from the ground. The bird is taking her own picture by 

 sitting on a string which was attached to the shutter of a camera placed in a 

 near-by tree. (Photo, by Hegner.) 



Certain hairlike feathers occur about the mouth and some- 

 times on other parts of the body ; these are known as filoplumes. 

 Feathers are not embedded in all parts of the skin, but those 

 parts of the body without them are covered by feathers from 

 other regions. 



Molting. — All birds change their feathers frequently. The 

 young, when newly hatched, are either naked or covered with 

 down. They soon outgrow this, just as young children outgrow 

 their clothes, and in the course of a week or two true feathers 



