UTILITY OF BIRDS IN NATURE. 5 
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 Arche- 
opteryx, had teeth, 
two fingers on each 
wing, and along 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- Fig. 1.—The Archzopteryx, a bird with teeth. Re- 
ture of the blood is stored from the Jurassic epoch. About one-fifth natural 
7 - . size; after Chapman. 
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- 
