RAPIDITY OF FLIGHT. 
97 
throat, a large pouch communicating with the lungs, 
and with the hollow and particularly light hone- 
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 atmo- 
sphere. And that this is the case, may be presumed 
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, sus- 
pended 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 
VOL. i. H 
