The Audubon Societies 53 



sufficient gasoline to drive it only a relatively few hundred miles before it has to 

 descend. But what of the birds? Think of the Golden Plover that starts on a 

 non-stop trip from Nova Scotia to northern South America or from Alaska to 

 the Hawaiian Islands, distances of over 2,500 miles, with only the fat stored up 

 on their bodies to serve as fuel. Surely gasoline is not the last word in fuel for 

 aeroplanes. 



If one watches the captive bird closely, he can see the feathers of its breast 

 and elsewhere pulsating in accord with the throbbing of the heart. If one counts 

 the pulsations, he will learn how rapidly the heart of a bird beats compared with 

 that of man, and that means how much more rapidly all of its processes work. 

 The bird's temperature is normally nearly ten degrees higher than that of man, 

 and that means that its tissues are burned up and replaced much more rapidly. 



A DUCK HAWK PURSUING A SWALLOW, ILLUSTRATING WITH BOTH BIRDS THE 

 MODERATELYLONG, POINTED WINGS BEST ADAPTED FOR SPEED OF LONG DURATION. 



Photographed by H. H. Knight 



and it means that energy in the form of muscular power is liberated much more 

 rapidly. What a strange misshapen creature man would be if he had relatively 

 the muscular power of a bird. 



And so in these four respects, in their modifications for lightness, strength, 

 compactness, and power, birds are all much alike in spite of their many apparent 

 differences. But birds do not all fly alike or in equal amounts, nor are their 

 modifications all carried to the same extreme. As is well known, some birds, like 

 the Ostrich, the Penguins, and certain birds of New Zealand have lost entirely 

 the power of flight; and birds like the domestic fowl are far inferior to the Hawk 

 or the Eagle. It is interesting to note the differences in the flight of different 

 groups of birds and to try to find differences in the structure of the birds or the 

 shapes of their wings correlated with the differences. Thus, if we consider the 

 wings of a Bluebird or a Crow as of normal or average proportions and their 



