98 RAPIDITY OF FLIGHT. 



and with the hollow and particularly light bone- 

 work of its skeleton. Suppose, then, that the bird 

 wishes to rest in the air; in the first place, it 

 avails itself of its large wings, which it is enabled 

 by constant habit to keep expanded, and which are 

 in themselves nearly sufficient to sustain its weight 

 and float its light body in the air. But, in addition 

 to the wing, suppose the bird fills its large pouch 

 with air, and from thence forces it into all its bones 

 and cavities between the flesh and the skin, what 

 will happen? That the heat of its circulation (and 

 it is well known that the heat of a bird's circulation 

 is considerably beyond that of other animals,) will 

 rarefy the internal air; which will, therefore, puff 

 up, not only the pouch, but every cavity, and thus 

 give the bird a surprising additional buoyancy or 

 power of floating, even in the higher regions of the 

 atmosphere. And that this is the case, may be pre- 

 sumed from its habits; for when the lower currents 

 of air are stormy and disagreeable, up goes the 

 Frigate-Bird to a higher and calmer current, where, 

 just as we see the light fleecy clouds in the sky, it 

 remains, suspended with outspread wing, motionless, 

 and at rest, till roused by hunger, it expels the 

 rarefied air, and, emptying its pouch, descends towards 

 the waves; but as it never either dives or swims, on 

 approaching within a few feet, it instantly stops, 

 and changes its direction, so as to skim along and 

 catch the flying-fish with its hawk-like bill or talons, 

 or both together. So averse are they, in fact, to 

 diving, or even touching the water, that, instead 

 of dashing downwards head foremost, like the 

 Gannet and other diving birds, the Frigate-Bird 



