These birds are usually seen singly or in pairs, and are pre-eminently oceanic, seldom coming to land except near the breeding quarters, where they roost on the trees; the normal flight is extremely rapid, graceful, and long-sustained, with sudden deviations from the course, but they often soar until they appear mere specks in the sky, descending thence with great abruptness. At times they float aloft with little apparent movement of the wide-spread wings, alternately opening and shutting the forked tail and inclining the head from side to side, while in hurricanes they fly low before the gale. At rare intervals they are found sitting asleep upon the shore. Flocks frequently pursue the surface-swimming fish, constituting their main aliment, which are seized almost without ruffling the water; squids, small crabs, flying fish, and young turtles being also eaten. To see a Frigate-bird plunge, however, is no uncommon occurrence, and the habit of forcing Terns, Boobies, and the like to disgorge their prey, which is caught before it reaches the waves, must not be forgotten.[85] If secured in an awkward position the captures are tossed up in the air, caught again and swallowed. The note, a harsh croak or cackle, is seldom heard. The nest of small sticks, which the birds tear off upon the wing, is generally in trees or bushes, though occasionally on the ground or on a bare rock; it is often {83}very slight, and almost invariably contains one egg, resembling that of the Cormorant. The young are fed by regurgitation, and both sexes are said to incubate, sitting very closely, and merely snapping at an intruder. The feathers are used for head-dresses in the Pacific Islands.