from such a hight he would lose sight of the fish before he reached the water. 

 The flycatcher sitting erect upon its perch watching passing insects that are often 

 invisible to the human eye, in like manner utilizes the pecten in the perception, 

 pursuit and capture of its prey. Most of the smaller birds will see a hawk in 

 the sky before it becomes visible to the human eye. The vulture, floating on wide 

 wings in upper air, discerns his chosen food in the valley far below ; as he descends 

 toward it he is seen by others wheeling in the distant sky. As they turn to 

 follow him they are also seen by others soaring at greater distances, who, follow- 

 ing, are pursued afar by others still, until a feathered host concenters from the 

 sky upon the carrion feast. 



They surpass all other vertebrate animals in breathing power or lung 

 capacity, as well as in muscular strength and activity. The temperature 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 

 mount 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 migrations that, when shot, their distended 

 skins burst open when their bodies strike the ground. This accumulation of fatty 

 tissue may aid to tide the birds over a season of scarcity, but the moment they need 

 food they must seek it far and wide, if need be, as they cannot live long without it. 



Certain moths deposit hundreds of eggs in a season, and were each egg to 

 hatch and each insect come to maturity and go on producing young at the same 

 rate, the entire earth in a few years would be carpeted with crawling caterpillars, 

 and the moths in flight would cover the earth like a blanket of fog. But under 

 natural conditions the caterpillars that hatch from the eggs of the moth are 

 destroyed by birds, mammals, insects or other animals, by disease or the action of 

 the elements, so that in the end only one pair of moths succeeds another. If every 

 robin should produce five young each year, and each robin should five fifteen years, 

 in time every square foot of land on this continent would be packed with robins, 

 but the surplus robins are killed and eaten by various other birds or by mammals, 

 each striving to maintain itself; so that, eventually, the number of robins remains 

 about the same. 



Thus we see that while birds, insects, other animals and plants are constantly 

 striving to increase their numbers, the creatures that feed upon them operate con- 

 tinually to check this undue multiplication. The hawk preys upon the smaller 

 birds and mammals. The smaller birds and mammals feed on insects, grass seeds, 

 leaves and other animal and vegetable food, each virtually endeavoring to gain 

 strength and increase the numbers of its race at the expense of other living 

 organisms. 



91 



