UTILITY OF BIRDS IN NATURE. 



sued from afar by others still, until a feathered host con- 

 centers from the sky upon the carrion feast. 



Birds are lower in the organic scale than the class of 

 mammals which includes man, the four-footed animals, and 

 even the seal and the whale. Birds are closely allied in 

 structure to reptiles. The earliest bird known, the Archte- 

 opteryx, had teeth, 

 two fingers on each 

 wing, and a long rep- 

 tilian tail adorned 

 with feathers . Still, 

 notwithstanding the 

 comparatively low 

 place which is given 

 by the systematists 

 to birds, their 

 physical organiza- 

 tion excels in some 

 respects that of all 

 otheranimals. They 

 surpass all other 

 vertebrate animals 

 in breathing power 

 or lung capacity, as 

 well as in muscular 

 strength and activ- 

 ity. The tempera- 

 ture of the blood is 

 higher in birds than 

 in other animals, and the circulation is more rapid. To 

 maintain this high temperature, rapid circulation, and great 

 activity, a large amount of food is absolutely necessary. 

 Food is the fuel without which the brightly burning fires 

 of life must grow dim and die away. Birds are, therefore, 

 fitted for their function of aerial police not only by their 

 powers of flight and perception, but also by their enormous 

 capacity for assimilating food. When food is plentiful, 

 birds gorge themselves, accumulating fat in quantities. 

 Shore birds frequently become so fat during the fall migra- 



Fig. 1. — The Archseopteryx, a bird with teeth. Re- 

 stored Irom the Jurassic epoch. Ahout one-fllth natural 

 size; after Chapman. 



