190 



ANIMALS CLASSIFIED 



The rate of respiration, of heartbeat, and the body temperature 

 are all higher in the bird than in man. Man breathes from twelve 

 to fourteen times per minute. Birds breathe from twenty to sixty 

 times a minute. Because of the increased activity of a bird, 

 there comes a necessity for a greater and more rapid supply of 

 oxygen, an increased blood supply to carry the material to be 

 used u\) in the release of energy, and a means of rapid excretion 

 of the wastes resulting from the process of oxidation. Birds are 



Common torn and young, showing nesting and feeding habits. (From group 

 at American Museum of Natural History.) 



large eaters, and the digestive tract is fitted to digest the food 

 quickly, by having a large crop in which food may be stored in a 

 much softened condition. As soon as the food is part of the blood, 

 it may be sent rapidly to the places where it is needed, by means 

 of the large four-chambered heart and large blood vessels. 



The high temperature of the bird is a direct result of this rapid 

 oxidation ; furthermore, the feathers and the oily skin form an 

 insulation which does not readily permit of the escape of heat. 

 This insulating cover is of much use to the bird in its flights at 



