Frigate-Bird

Frigate-Bird, the name commonly given by English sailors, on account of the swiftness of its flight, its habit of cruising about near other species and of daringly pursuing them, to a large sea-bird1—the Fregata aquila of most ornithologists—the Fregatte of French and the Rabihorcado of Spanish mariners. It was placed by Linnaeus in the genus Pelecanus, and its assignment to the family Pelecanidae had hardly ever been doubted till Professor St George Mivart declared (Trans. Zool. Soc. x. p. 364) that, as regards the postcranial part of its axial skeleton, he could not detect sufficiently good characters to unite it with that family in the group named by Professor J. F. Brandt Steganopodes. There seems to be no ground for disputing this decision so far as separating the genus Fregata from the Pelecanidae goes, but systematists will probably pause before they proceed to abolish the Steganopodes, and the result will most likely be that the frigate-birds will be considered to form a distinct family (Fregatidae) in that group. In one very remarkable way the osteology of Fregata differs from that of all other birds known. The furcula coalesces firmly at its symphysis with the carina of the sternum, and also with the coracoids at the upper extremity of each of its rami, the anterior end of each coracoid coalescing also with the proximal end of the scapula. Thus the only articulations in the whole sternal apparatus are where the coracoids meet the sternum, and the consequence is a bony framework which would be perfectly rigid did not the flexibility of the rami of the furcula permit a limited amount of motion. That this mechanism is closely related to the faculty which the bird possesses of soaring for a considerable time in the air with scarcely a perceptible movement of the wings can hardly be doubted.

Two species of Fregata are considered to exist, though they differ in little but size and geographical distribution. The larger, F. aquila, has a wide range all round the world within the tropics and at times passes their limits. The smaller, F. minor, appears to be confined to the eastern seas, from Madagascar to the Moluccas, and southward to Australia, being particularly abundant in Torres Strait,—the other species, however, being found there as well. Having a spread of wing equal to a swan’s and a very small body, the buoyancy of these birds is very great. It is a beautiful sight to watch one or more of them floating overhead against the deep blue sky, the long forked tail alternately opening and shutting like a pair of scissors, and the head, which is of course kept to windward, inclined from side to side, while the wings are to all appearance fixedly extended, though the breeze may be constantly varying in strength and direction. Equally fine is the contrast afforded by these birds when engaged in fishing, or, as seems more often to happen, in robbing other birds, especially boobies, as they are fishing. Then the speed of their flight is indeed seen to advantage, as well as the marvellous suddenness with which they can change their rapid course as their victim tries to escape from their attack. Before gales frigate-birds are said often to fly low, and their appearance near or over land, except at their breeding-time, is supposed to portend a hurricane.2 Generally seen singly or in pairs, except when the prospect of prey induces them to congregate, they breed in large companies, and O. Salvin has graphically described (Ibis, 1864, p. 375) one of their settlements off the coast of British Honduras, which he visited in May 1862. Here they chose the highest mangrove-trees3 on which to build their frail nests, and seemed to prefer the leeward side. The single egg laid in each nest has a white and chalky shell very like that of a cormorant’s. The nestlings are clothed in pure white down, and so thickly as to resemble puff-balls. When fledged, the beak, head, neck and belly are white, the legs and feet bluish-white, but the body is dark above. The adult females retain the white beneath, but the adult males lose it, and in both sexes at maturity the upper plumage is of a very dark chocolate brown, nearly black, with a bright metallic gloss, while the feet in the females are pink, and black in the males—the last also acquiring a bright scarlet pouch, capable of inflation, and being perceptible when on the wing. The habits of F. minor seem wholly to resemble those of F. aquila. According to J. M. Bechstein, an example of this last species was obtained at the mouth of the Weser in January 1792.