Sharing the tropical oceans with the Tropic-birds are the so-called Frigate-birds or Man-o’-war Birds, of which three forms only are known. They are very powerful flying birds from thirty to forty inches in length, remarkable at once for the extremely short tarsus, greatly elongated wings, and a long, deeply forked swallow-like tail. In the mature males the plumage is black throughout,though the adult male of F. ariel 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 extremely 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 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 industrious 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 to be a sort of way of resting. The circles were of about one hundred feet diameter; the flight very regular, slow, and monotonous, with no apparent motion of the wings for hours. It tired me to look at them.”
Of the two species the larger (F. Aquila) is found in tropical and subtropical seas of both hemispheres, chiefly north of the equator, coming north in this country regularly to Florida, Texas, and California, and casually to Nova Scotia. A smaller form of this (F. A. Minor) is found in the central Pacific and Indian oceans, while the still smaller and quite distinct F. ariel, the male of which has a conspicuous white flank-patch, occurs also in the tropical and subtropical portions of the same oceans. The Frigate-birds nest in colonies throughout their range, building a very slight nest on mangroves and other low trees, or on the ground. The egg is usually single, pure white, and about two and seventy hundredths by one and seventy-five hundredths inches.
Following is an account, by Mr. J. J. Lister, of a visit to the Phoenix Islands in the South Pacific, where he found the Lesser Frigate-bird (F. A. Minor) breeding in great numbers. He says: “From the boat I went off to the part of the island over which the Frigate-birds were wheeling. Here I found their nests in great numbers. They were built of small dead twigs of the plants of the island, placed a foot or so above the ground on the spreading branches of the Sida (a shrubby, malvaceous plant two or three feet high) and on the beaten-down tussocks of grass. The nests were placed as near together as supports could be found, and there were well-defined limits to the colonies, although the bushes beyond these limits appeared to be just as well suited for the purpose as those within. Each nest was occupied by a bird. As one approached some of these took flight and joined the whirling crowd overhead, but the rest remained sitting and allowed themselves to be touched with the muzzle of my gun, only chattering their bills by way of remonstrance. Both males and females were to be seen engaged in the duties of incubation.
“The throat-pouch of the male is a most striking object. When fully distended it reaches forward as far as the end of the bill and downwards so as to completely hide the breast, a great smooth semi-transparent balloon of the most brilliant scarlet, which contrasts finely with the dark metallic tints of the plumage. If any of the birds in a group had their pouches distended, there were generally several in this condition, as though they were vying with one another in the exhibition of their attractions. From several parts of the group came a low, vibrating note, a combination of a whistle and a purr, accompanied by the sound of the chattering of their bills. While uttering this note the bird leans back on the nest, with the head thrown right back, the pouch fully extended, and the wings half spread and shaken with a quivering movement. The female birds mean-while were either whirling overhead or sitting on the edge of the nest near their admirers.
“The pouch is not rapidly filled or emptied; when a bird with a half-distended pouch takes flight, the latter is carried from side to side with the movement through the air, gradually diminishing in size. In the undistended state the bare, wrinkled skin is completely retracted to the level of the general contour of the neck. The interior of the pouch is in communication with the air sacs of the neck; it is therefore filled and emptied through the bronchi.
” By far the greater number of nests on Phoenix Island contained a single white egg about as large as a hen’s; some nests, however, contained two eggs. Mr. Lister also mentions seeing the Frigate-birds drinking from the fresh-water lagoons. As they came “sweeping down to the surface, they scooped up the water with the lower mandible.”