Frigate-birds 137 



though the adult male of jP. arid has conspicuous white flank-patches, while 

 the feathers of the back are glossed with metallic green and reddish purple. 

 The females are blackish above but have the breast and sides white, while the 

 immature young have the head, neck, and upper part of the chest as well as the 

 middle of the lower breast and abdomen white. Further distinguishing marks 

 are afforded by the very long, strongly hooked bill, the flattened, fringed claw on 

 the middle toe, and the very narrow web. The bones of the skeleton are ex- 

 tremely pneumatic, perhaps more so than in any other bird, for the Frigate-bird 

 is a marvel of lightness and grace on the wing. In the male there is a curious 



FIG. 42. Frigate-bird, Fregata aquila. 



pouch under the bill which is capable of inflation at the will of the bird to some- 

 times half or more the size of the body. This is bright scarlet in color, and 

 contrasts strongly with dark plumage. 



The food of the Frigate-birds consists of fish, a part of which they capture 

 themselves, but in the main they apparently subsist by robbing the more indus- 

 trious Gannets and Terns. On observing a successful fisherman they give chase, 

 and no matter how fast he may fly or how often he may turn, the pursuer is always 

 at hand, and finally in despair he drops the fish, which is caught before it can reach 

 the water. 



The Frigate-birds may often be seen soaring at vast heights, from which they 

 often drop like an arrow. Scott, who saw them about the Dry Tortugas, says: 

 "Almost every day about noon a party of from four to twenty of these birds (F. 

 aquila) came to Garden Key, and attaining a point just above the Harbor Light 

 Tower on the northeast wall of the fort, they would begin to soar in what seemed 



