The Birds 



of both the birds and mammals is determined by the environ- 

 ment surrounding them and all the many thousands of differ- 

 ent forms into which they have developed is directly trace- 

 able to their food supply. The most distinguishing mark of 

 birds above all other creatures is that of feathers which are 

 designed for both strength and lightness and fits them for 

 the power of flight. Their feet and toes are still covered 

 in a modified form with the ancestral scales of the lizard. 

 Their internal structure has been modified to meet modifica- 

 tions of their bodily forms. In the far distant past, they 

 developed their upper and lower jaws into hornlike bills or 

 beaks. These have a great variety of forms depending on 

 the kind of food upon which they live. The necks are either 

 long, short or of medium lengths depending entirely upon 

 their food and environment. The forellmbs have developed 

 into wings with the same number of bones as are found in 

 the other vertebrates. The hand of their ancestors has been 

 developed Into a flattened bone Indicating the joining of the 

 several bones of the hand. 



Their circulatory system is developd to a high degree, 

 which together with their air chambered covering of feathers, 

 gives to them an even body temperature ranging from 102° 

 to 100° Fahrenheit. Because of their pure blood and high 

 body temperature, they are unusually active in their habits 

 and develop a great amount of endurance. In some species 

 during their period of rapid growth, the young will consume 

 food in quantities equal to three times their own weight in a 

 single day. 



Their ancestral teeth were cast off before the seeds and 

 grain had developed Into their present hardness. To over- 



[217] 



