Degland & Gerbe, 1867
The frigatebirds (also known as Fregatidae) are a family of seabirds. They have long wings, tails, and bills and the males have a red gular pouch that is inflated during the breeding season to attract a mate. Their plumage is predominantly black. There are five living species, all in a single genus Fregata, found across all tropical and subtropical oceans. They are absent from polar regions. Long placed in the Pelecaniformes, they are now reclassified in the order Suliformes and appear to be only distantly related to pelicans. The frigatebird family is the sister group to the Suloidea (cormorants, darters, and gannets and boobies). Three fossil species of the prehistoric Eocene genus Limnofregata are known from North America. These had longer legs, less-hooked bills and shorter wings, and at least two of them lived in a freshwater habitat.
Frigatebirds are pelagic piscivores that obtain most of their food on the wing. A small amount of their diet is obtained by robbing other seabirds and by snatching seabird chicks. Frigatebirds are seasonally monogamous, and nest colonially. A rough nest is constructed in low trees or on the ground on remote islands. A single egg is laid each breeding season.
Christopher Columbus encountered frigatebirds when passing the Cape Verde Islands on his first voyage across the Atlantic in 1492. In his journal entry for 29 September he used the word rabiforçado, modern Spanish rabihorcado or forktail.[a] The word frigatebird derives from the French mariners' name for the bird La Frégate - a frigate or fast warship. The etymology was mentioned by French naturalist Jean-Baptiste du Tertre when describing the bird in 1667.[b] In the Caribbean frigatebirds were called Man-of-War birds by English mariners. This name was used by the English explorer William Dampier in his book An Account of a New Voyage Around the World published in 1697:
The Man-of-War (as it is called by the English) is about the bigness of a Kite, and in shape like it, but black; and the neck is red. It lives on Fish yet never lights on the water, but soars aloft like a Kite, and when it sees its prey, it flys down head foremost to the Waters edge, very swiftly takes its prey out of the Sea with his Bill, and immediately mounts again as swiftly; never touching the Water with his Bill. His Wings are very long; his feet are like other Land-fowl, and he builds on Trees, where he finds any; but where they are wanting on the ground.
The modern name Frigate Bird was used in 1738 by the English naturalist and illustrator Eleazar Albin in his A Natural History of the Birds. The book included an illustration of the male bird showing the red gular pouch.
Frigatebirds were grouped with cormorants, and sulids (gannets and boobies) as well as pelicans in the genus Pelecanus by Linnaeus in 1758 in the tenth edition of his Systema Naturae. He described the distinguishing characteristics as a straight bill hooked at the tip, linear nostrils, a bare face, and fully webbed feet. In 1874, English zoologist Alfred Henry Garrod published a study where he had examined various groups of birds and recorded which muscles of a selected group of five[c] they possessed or lacked. Noting that the muscle patterns were different among the steganopodes (classical Pelecaniformes), he resolved that there were divergent lineages in the group that should be in separate families, including frigatebirds in their own family Fregatidae. Urless N. Lanham observed in 1947 that frigatebirds bore some skeletal characteristics more in common with procellariiformes than pelecaniformes, though concluded they still belonged in the latter group (as suborder Fregatae), albeit as an early offshoot. The classification of this group as the traditional Pelecaniformes, united by totipalmate feet and the presence of a gular pouch, persisted until the early 1990s. Molecular studies showed that pelicans, the namesake family of the Pelecaniformes, are actually more closely related to herons, ibises and spoonbills, the hamerkop and the shoebill than to the remaining members. In recognition of this, the order was renamed Suliformes in 2010.
In 1994 the family name Fregatidae, cited as described in 1867 by French naturalists Côme-Damien Degland and Zéphirin Gerbe, was conserved under Article 40(b) of the International Code of Zoological Nomenclature in preference over the 1840 description Tachypetidae by Johann Friedrich von Brandt.
A cladistic study of the skeletal and bone morphology of the classical Pelecaniformes and relatives found that the frigatebirds formed a clade with the Eocene fossil frigatebird genus Limnofregata. Birds of the two genera have 15 cervical vertebrae, unlike almost all other Ciconiiformes, Suliformes and Pelecaniformes, which have 17. This group is sister group to the group Suloidea, which comprises the gannets and boobies, cormorants and darters. The age of Limnofregata indicates that these lineages had separated by the Eocene.
The Eocene frigatebird genus Limnofregata comprises birds whose fossil remains were recovered from prehistoric freshwater environments, unlike the marine preferences of their modern-day relatives. They had shorter less-hooked bills and longer legs, and longer slit-like nasal openings. Three species have been described: two from the Green River Formation (48-52 million years old) and one from the Wasatch Formation (between 53 and 55 million years of age).
Fossil material indistinguishable from living species dating to the Pleistocene and Holocene has been recovered from Ascension Island (for F. aquila), Saint Helena Island, and various islands elsewhere in the Pacific Ocean (for F. minor and F. ariel).
Living species and infrageneric classification
The genus Fregata was defined by French naturalist Bernard Germain de Lacépède in 1799. Veillot described the genus name Tachypetes in 1816 for the great frigatebird. The genus name Atagen was coined by Paul Möhring in 1752, though this has no validity as it predates the official beginning of Linnaean taxonomy. The type species is the Ascension frigatebird (Fregata aquila). For many years, the consensus was to recognise only two species of frigatebird, with larger birds as F. aquila and smaller as F. ariel. The Australian ornithologist Gregory Mathews delineated five species, which remain valid. Analysis of ribosomal and mitochondrial DNA indicated that the five species had diverged from a common ancestor only recently—as little as 1.5 million years ago. There are two species pairs, the great and Christmas Island frigatebirds, and the magnificent and Ascension frigatebirds, while the fifth species, the lesser frigatebird, is an early offshoot of the common ancestor of the other four species.
|Living species of frigatebirds|
|Common and binomial names||Image||Description||Range|
|Largest species with body length of around 100 cm (39 in). The adult male is all-black with a scarlet throat pouch that is inflated like a balloon in the breeding season. Although the feathers are black, the scapular feathers produce a purple iridescence when they reflect sunlight, in contrast to the male great frigatebird's green sheen. The female is black, but has a white breast and lower neck sides, a brown band on the wings, and a blue eye-ring.||Widespread in the tropical Atlantic, breeding colonially in trees in Florida, the Caribbean and Cape Verde Islands. It also breeds along the Pacific coast of the Americas from Mexico to Ecuador, including the Galápagos Islands.|
|Male: Apart from smaller size, very similar to the magnificent frigate bird. Female: brownish black with a rusty brown mantle and chest. Females normally lack any white patches present on the front of female birds of other species. The occasional female observed with a white belly may be breeding before obtaining the full adult plumage.||Boatswain Bird Island just off Ascension Island in the tropical Atlantic Ocean. vulnerable|
|Male: Only species with white on belly - an egg shaped patch. Larger with a longer bill than Great. Upper surface black with green metallic gloss on the mantle and scapulars. Female: Upper surface dark with brown wing bars. Head black with white belly and white collar (sometimes incomplete) around neck.||Christmas Island in the Indian Ocean. Critically endangered|
|Male: Underneath completely black with subtle brown barring on the axillaries. Upper surface black with green metallic gloss on the mantle and scapulars. Female: Upper surface dark with lighter brown wing bars. Head black with mottled throat and belly. White collar around neck.||Tropical oceans worldwide|
|Smallest species, body length of around 75 cm (30 in). Male: Black underneath except for bold white axillary spurs. Upper surface black with greenish to purple metallic gloss on the mantle and scapulars. Female: Upper surface dark with lighter wing bars. Head black with white belly and white collar around neck.||Tropical and subtropical waters across the Indian and Pacific Oceans. Atlantic race trinitatis limited to Trindade, off Eastern Brazil.|
Frigatebirds are large slender mostly black-plumaged seabirds, with the five species varying little in appearance. Females are larger than males, and generally have white markings on their underparts. Frigatebirds have short necks and long, narrow wings (male wingspan can reach 2.3 metres (7.5 ft)) tapering to points. Their tails are deeply forked, though this is not apparent unless the tail is fanned. The legs and face are full feathered. The totipalmate feet are short and weak, the webbing is reduced and part of each toe is free.
The males have inflatable red-coloured throat pouches called gular pouches, which they inflate to attract females during the mating season. The gular sac is, perhaps, the most striking frigatebird feature.
Frigatebirds produce very little oil and therefore do not land in the ocean.
Distribution and habitat
Frigatebirds are found over tropical oceans, and ride warm updrafts under cumulus clouds. They have a large wing area for their weight which allows them to continually soar and only rarely flap their wings. Like swifts they are able to spend the night on the wing, but they will also return to an island to roost.
Behaviour and ecology
Frigatebirds do not swim and with their short legs cannot walk well. Having the largest wingspan-to-body-weight ratio of any bird, they are essentially aerial, able to stay aloft for long periods, landing only to roost or breed on trees or cliffs. Field observations in the Mozambique Channel found that great frigatebirds could remain on the wing for up to 12 days while foraging.
The average life span is unknown but in common with seabirds such as the wandering albatross and Leach's storm petrel, frigatebirds are long-lived. In 2002 35 ringed great frigatebirds were recovered on Tern Island in the Hawaiian Islands. Of these ten were older than 37 years and one was at least 44 years of age.
Frigatebirds' feeding habits are pelagic, and they may forage up to 500 km (310 mi) from land. They do not land on the water but snatch prey from the ocean surface using their long, hooked bills. They mainly catch small fish such as flying fish that are driven to the surface by predators such as tuna, but they will also eat squid. Frigatebirds will rob other seabirds such as boobies, tropicbirds, and shearwaters of their catch, using their speed and manoeuvrability to outrun and harass their victims until they regurgitate their stomach contents. Although frigatebirds are renowned for their kleptoparasitic feeding behaviour, kleptoparasitism is not thought to play a significant part of the diet of any species, and is instead a supplement to food obtained by hunting. A study of great frigatebirds stealing from masked boobies estimated that the frigatebirds could at most obtain 40% of the food they needed, and on average obtained only 5%.
Frigatebirds typically breed on remote oceanic islands. Male birds display to females flying overhead by pointing their bills upwards, inflating their red throat pouches and vibrating their outstretched wings. They produce a drumming sound by vibrating their bills together and sometimes give a whistling call. After copulation it is generally the male who gathers sticks and the female that constructs the loosely woven nest. Frigatebirds prefer to nest in trees or bushes but when these are not available they will nest on the ground. A single white egg is laid which is incubated in turns by both birds for 41-55 days. The altricial chicks are naked on hatching and develop a white down. They are continually guarded by the parents for the first 4-6 weeks and are fed on the nest for 5-6 months. Both parents take turns feeding for the first three months but then only the mother feeds the young for another eight months. It takes so long to rear a chick that frigatebirds cannot breed every year. It is typical to see juveniles as big as their parents waiting to be fed. When they sit waiting for endless hours in the hot sun, they assume an energy-efficient posture in which their head hangs down, and they sit so still that they seem dead. But when the parent returns, they will wake up, bob their head, and scream until the parent opens its mouth. The hungry juvenile plunges its head down the parent's throat and feeds at last.
The duration of parental care in frigatebirds is among the longest for birds, rivalled only by the southern ground hornbill and some large accipitrids. Frigatebirds take many years to reach sexual maturity. A study of great frigatebirds in the Galapagos Islands found that they only bred once they have acquired the full adult plumage. This was attained by female birds when they were eight to nine years of age and by male birds when they were 10 to 11 years of age.
In Nauru, catching frigatebirds was an important tradition. It is still practised to a lesser degree. Donald W. Buden writes: "Birds typically are captured by slinging the weighted end of a coil of line in front of an approaching bird attracted to previously captured birds used as decoys. In a successful toss, the line becomes entangled about the bird’s wing and bringing [sic] it to ground."
- Columbus's journal survives in a version recorded by Bartholomé de las Casas in the 1530s. In English the entry reads: "They saw a bird that is called a frigatebird, which makes the boobies throw up what they eat in order to eat it herself, and she does not sustain herself on anything else. It is a seabird, but does not alight on the sea nor depart from land 20 leagues. There are many of these on the islands of Cape Verde."
- Du Tertre wrote: "Loyseau que les habitans des Indes appellent Fregate (à cause de la vistesse de son vol) n'a pas le corp plus gros qu'une poule ...".
- ambiens, fermorocaudal, accessory femorocaudal, semitendinosus, and accessory tendinosus
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|Wikimedia Commons has media related to Fregatidae.|
- Frigatebird videos, photos and sounds on the Internet Bird Collection
- Chisholm, Hugh, ed. (1911). "Frigate-bird". Encyclopædia Britannica (11th ed.). Cambridge University Press.