GROUPS OF ANIMALS 



259 



the barks of trees; others, such as the vulture, have 

 strong, curved beaks for tearing their prey. 



In many ways the body of the bird is especially fitted 

 for flying. Many of the bones of the skeleton are hol- 

 low, thus combining lightness and strength. The breast 

 bone is greatly developed for the attachment of the 



Permission of Field Museum of Natural History. 

 Fig. 115. Adaptations in the bills of birds. 



large muscles used in flying. The rounded body with 

 its smooth covering of feathers offers little resistance 

 in flying. 



Because of the very active life of birds, the rate of 

 respiration, the rate of the heart beat, and the tem- 

 perature of the body are all- higher than in any other 

 animal. Birds breathe from 20 to 60 times a minute. 



