Distinguishing Characteristics

Large, unmistakable, black to dark-brownish seabird, characterized by extremely long, pointed wings; long, deeply forked tail; and long, hooked bill. Length 89–114 cm, wing span 217–244 cm (Harrison 1983), mass 1,000–1,900 g (Table 1). Typically observed soaring or perched; soars easily, flapping only occasionally, with deep, slow wing-beats; rarely, if ever, observed sitting on the water. Legs so short they preclude walking; feet very small, all 4 toes connected by webbing (toti-palmate) but webbing shallow, not reaching tips of toes. Following plumage descriptions based largely on Howell 1994 .

Adult Plumages

Sexes differ in size and plumage coloration. Male smaller than female (Table 1) and entirely black, except for brownish inner secondaries on upper wing, and patch of bare skin (gular sac) on lower neck. Gular sac becomes bright red and is inflated like a large balloon during courtship displays and early incubation period, but becomes pale orange and shrinks to become barely visible at other times of the year. At close range, male also glossed purple on head and green on neck, scapulars, and upper wing. Male legs and feet black or gray to brownish black.

Female entirely blackish brown except for prominent white patch across breast and uppermost belly (extending variably to sides of neck and with a narrow wedge of dark color extending from throat onto center of upper breast), white tips across axillaries forming 3–4 lines on underwing, and a pale tan to dirty white ‘alar’ bar on upper wing which extends diagonally inward from the crook on leading edge of wing. Head and upperparts with less extensive gloss than male (mostly restricted to back of head and neck), and gular sac absent. Female legs and feet flesh-colored to pink.

No distinct seasonal change in adult appearance except for changes in appearance of male gular sac during breeding period. No distinct geographic variation in plumage coloration recognized, but some geographic variation in size occurs.

Subadult Plumages

Juvenal plumage similar to adult female except juvenile head entirely white, and a V-shaped wedge of black extends from each side inwardly onto lower breast; legs, feet, and bill light-bluish gray. Juvenal-plumage aspect believed to be retained for 18–24 mo (Howell 1994), but this awaits confirmation through observations of marked individuals. Plumage gradually changes to adult coloration. Sexes become differentiated during this period, probably around age 3 yr. For more detailed descriptions of adult and subadult plumages, see Howell 1994 .

Similar Species

Difficult to distinguish from other frigatebird species in flight. Within the Americas and in the Hawaiian Is., slightly smaller Great Frigatebird species most likely to be confused with Magnificent Frigatebird. Adult male Magnificent distinguished from adult male Great by lack of pale alar bar on upper wing (present in Great), (usually) all-black axillaries (axillaries with pale tips in Great), and gray to black legs and feet (pink to reddish in Great). Adult female Magnificent distinguished from adult female Great by black chin and throat (chin and lower throat grayish in Great); blue orbital ring, which may be difficult to see (red and often noticeable in Great), pale blue-gray to gray bill (fleshy blue-gray to flesh-pink in Great except in Galápagos Is., and Baker I., Pacific Ocean, where same color as Magnificent); shape of black area on belly which protrudes forward into white breast patch (best viewed in flight from directly underneath) narrower and more tapered in Magnificent (broader and more rounded in Great); and lack of cinnamon clouding on white breast patch (often noticeable in Great). Juvenile Magnificent distinguished from juvenile Great by white head and breast (head and breast cinnamon to rusty or at least tinged with this color in Great), and by lower placement of black wedges on sides (wedges extend across lower breast in Magnificent but cross upper breast in Great). Latter feature creates distinct diamond-shaped white belly patch in juvenile Magnificent, while this patch more oval in juvenile Great. Subadults identified by their resemblance to Juvenal or adult plumages of their respective species.

Within the Americas, Magnificent could also be confused with Lesser Frigatebird (F. ariel) which breeds in the s. Atlantic but has occurred once in North America (Maine; Am. Ornithol. Union 1998). Magnificent distinguished from Lesser by distinctly larger size; orbital ring can be blue in Lesser; and lack of cinnamon color on head and breast in juvenile Magnificent (present in juvenile Lesser). For more detailed information on field identification of these species, see Harrison 1983 and Howell 1994 .