Frigatebirds

Frigatebirds are five species of oceanic birds that make up the family Fregatidae. Frigatebirds occur along the coasts of the tropical oceans, but also hundreds of miles out to sea.

Frigatebirds typically weigh about 3 lb (1.5 kg), but the spread of their long, narrow, swept-back, pointed wings can exceed 6.5 ft (2 m). These are highly favorable wing-loading characteristics, and frigate-birds are among the most skilled of the birds at flying and seemingly effortless gliding. Their tail is long, with extensive pointed forks. Their legs are short, and the small, partially webbed feet are only used for perching. Frigatebirds are very ungainly on the ground and in the water, on which they rarely set down.

The bill of frigatebirds is long, and both the upper and lower mandibles hook downwards. The plumage is a dark brownish black, with whitish underparts in some species, but the throat is naked and colored a bright red in males. The throat sac of male frigatebirds can be inflated with air and is used to impress the females, both visually and by helping to resonate the loud rattlings and yodels of courting males.

Frigatebirds are highly graceful and skilled aerialists. They are excellent fliers, both in terms of the distance they can cover across the vast oceans and their extremely skilled maneuverability in flight. They feed on fish, squid, jellyfish, and other invertebrates by hovering over the surface of the ocean and swiftly diving to snatch prey at the surface, often without getting their body feathers wet. Frigatebirds frequently catch flying fish during those brief intervals when both bird and fish are airborne. Frigatebirds sometimes prey on the young of other seabirds, especially terns and noddys.

Frigatebirds also commonly swoop aggressively on pelicans, boobies, and gulls, poking them and biting their tail and wings. This pugnacious behavior

forces these birds to drop or disgorge any fish that they have recently caught and eaten, which is then consumed by the frigatebird. Frigatebirds also force other seabirds to drop scarce nesting material, which is also retrieved. This foraging strategy is known to scientists as kleptoparasitism. In view of the well-deserved, piratical reputation of frigatebirds, they also are known as man-o-war birds.

Frigatebirds nest in trees or on remote, rocky ledges. Females bring sticks and other appropriate materials to the nest site, where the male constructs the nest. Both sexes of the pair share in incubating the eggs and raising their young. Frigatebirds do not migrate, but they may wander extensively during their non-breeding season.

The magnificent frigatebird (Fregata magnificens ) is a seasonally common seabird around the Florida Keys, and an occasional visitor elsewhere in the coastal southeastern and southwestern United States, ranging through the Caribbean, Gulf of Mexico, and western Mexico, and as far south as the Atlantic coast of Brazil, the Pacific coasts of Ecuador and Peru, and the Galapagos Islands. Male birds have a purplish black body and a bright red throat pouch. The females are browner and have a white breast, and juveniles are lighter brown and have a white head and breast.

Both the great frigatebird (Fregata minor ) and the lesser frigatebird (F. ariel ) have pan-tropical distributions, occurring in tropical waters over most of the world (but not in the Caribbean). Much more local distributions are exhibited by the Ascension frigate-bird (F. aquila ), which breeds only on Ascension Island in the South Atlantic, while the Christmas Island frigatebird (F. andrewsi ) only breeds on Christmas Island in the South Pacific Ocean. Both the Ascension frigatebird and the Christmas Island frigatebird are endangered, largely due to destruction of their breeding areas and predation and habitat degradation caused by introduced animals.

Bill Freedman