man-o'-war bird or frigate-bird, most aerial of the water birds, found in the tropic seas. The man-o'-war bird's wingspread (71/2 ft/228.5 cm) is the largest in proportion to its body (3–4 lb/1.4–1.8 kg) of any bird. It can soar motionless by the hour and has been recorded in flights lasting nearly four days, spending most of that time several hundred feet or more in the air. It is awkward on land and in the sea, where the feathers quickly become water-logged.
The name derives from its grace and swiftness in the air and from its piratical tendencies; it harasses boobies, pelicans, cormorants, and gulls until they drop their catch. Man-o'-war birds feed chiefly on fish but also prey on the young of sea birds and on jellyfish, squid, and young turtles. They have long hooked beaks and forked tails; the male has an inflatable orange throat pouch that becomes red at courtship time.
The purplish black magnificent frigate-bird, Fregata magnificens, 40 in. (100 cm) long, is found from the Bahamas and Baja California S to Brazil and Ecuador; the great frigate-bird, F. minor, is found in the Indian Ocean. Other species, e.g., the Ascension and Christmas Island frigate-birds, are named for their habitats. The lesser frigate-bird, the smallest (32 in./80 cm) of the family, is found in the South Pacific and on the islands off Brazil and Madagascar.
Frigate-birds are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Pelecaniformes, family Fregatidae.