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Frigatebirds are a family of
seabird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same envir ...
s called Fregatidae which are found across all
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
and subtropical oceans. The five extant species are classified in a single genus, ''Fregata''. All have predominantly black plumage, long, deeply forked tails and long hooked bills. Females have white underbellies and males have a distinctive red
gular pouch Gular skin (throat skin), in ornithology, is an area of featherless skin on birds that joins the lower mandible of the beak (or ''bill'') to the bird's neck. Other vertebrate taxa may have a comparable anatomical structure that is referred to as ...
, which they inflate during the breeding season to attract females. Their wings are long and pointed and can span up to , the largest wing area to body weight ratio of any bird. Able to soar for weeks on wind currents, frigatebirds spend most of the day in flight hunting for food, and roost on trees or cliffs at night. Their main prey are fish and squid, caught when chased to the water surface by large predators such as tuna. Frigatebirds are referred to as kleptoparasites as they occasionally rob other seabirds for food, and are known to snatch seabird chicks from the nest. Seasonally monogamous, frigatebirds 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. The duration of parental care is among the longest of any bird species; frigatebirds are only able to breed every other year. The Fregatidae are a sister group to
Suloidea The order Suliformes (, dubbed "Phalacrocoraciformes" by ''Christidis & Boles 2008'') is an order recognised by the International Ornithologist's Union. In regard to the recent evidence that the traditional Pelecaniformes is polyphyletic, it has ...
which consists of
cormorant Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven gen ...
s,
darter The darters, anhingas, or snakebirds are mainly tropical waterbirds in the family Anhingidae, which contains a single genus, ''Anhinga''. There are four living species, three of which are very common and widespread while the fourth is rarer and ...
s,
gannet Gannets are seabirds comprising the genus ''Morus'' in the family Sulidae, closely related to boobies. Gannets are large white birds with yellowish heads; black-tipped wings; and long bills. Northern gannets are the largest seabirds in the ...
s, and
boobies A booby is a seabird in the genus ''Sula'', part of the family Sulidae. Boobies are closely related to the gannets (''Morus''), which were formerly included in ''Sula''. Systematics and evolution The genus ''Sula'' was introduced by the Frenc ...
. Three of the five extant species of frigatebirds are widespread (the magnificent, great and lesser frigatebirds), while two are endangered (the
Christmas Island Christmas Island, officially the Territory of Christmas Island, is an states and territories of Australia, Australian external territory comprising the island of the same name. It is located in the Indian Ocean, around south of Java and Su ...
and
Ascension Island frigatebird The Ascension frigatebird (''Fregata aquila'') is a seabird of the frigatebird family Fregatidae which breeds on Boatswain Bird Island and Ascension Island in the tropical Atlantic Ocean. The Ascension frigatebird is a large lightly built se ...
s) and restrict their breeding habitat to one small island each. The oldest fossils date to the early Eocene, around 50 million years ago. Classified in the genus '' Limnofregata'', the three species had shorter, less-hooked bills and longer legs, and lived in a freshwater environment.


Taxonomy


Etymology

The term ''Frigate Bird'' itself was used in 1738 by the English naturalist and illustrator
Eleazar Albin Eleazar Albin (fl. 1690 – c. 1742)Michael A. Salmon, Peter Marren, Basil Harley. ''The Aurelian Legacy'' (University of California Press, 2000) pp. 109-110. was an English naturalist and watercolourist illustrator who wrote and illustrat ...
in his ''A Natural History of the Birds''. The book included an illustration of the male bird showing the red
gular pouch Gular skin (throat skin), in ornithology, is an area of featherless skin on birds that joins the lower mandible of the beak (or ''bill'') to the bird's neck. Other vertebrate taxa may have a comparable anatomical structure that is referred to as ...
. Like the genus name, the English term is derived from the French mariners' name for the bird ''la frégate''—a
frigate A frigate () is a type of warship. In different eras, the roles and capabilities of ships classified as frigates have varied somewhat. The name frigate in the 17th to early 18th centuries was given to any full-rigged ship built for speed and ...
or fast warship. The etymology was mentioned by French naturalist Jean-Baptiste Du Tertre when describing the bird in 1667. Alternative names and spellings include "frigate bird", "frigate-bird", "frigate", "frigate-petrel". Christopher Columbus encountered frigatebirds when passing the
Cape Verde Islands , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...
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. 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.


Classification

Frigatebirds were grouped with
cormorant Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven gen ...
s, and sulids (
gannet Gannets are seabirds comprising the genus ''Morus'' in the family Sulidae, closely related to boobies. Gannets are large white birds with yellowish heads; black-tipped wings; and long bills. Northern gannets are the largest seabirds in the ...
s and
boobies A booby is a seabird in the genus ''Sula'', part of the family Sulidae. Boobies are closely related to the gannets (''Morus''), which were formerly included in ''Sula''. Systematics and evolution The genus ''Sula'' was introduced by the Frenc ...
) 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. The genus ''Fregata'' was introduced by French naturalist
Bernard Germain de Lacépède Bernard-Germain-Étienne de La Ville-sur-Illon, comte de Lacépède or La Cépède (; 26 December 17566 October 1825) was a French naturalist and an active freemason. He is known for his contribution to the Comte de Buffon's great work, the ...
in 1799. The type species was designated as the Ascension frigatebird by French zoologist
François Marie Daudin François Marie Daudin (; 29 August 1776 in Paris – 30 November 1803 in Paris) was a French zoologist. With legs paralyzed by childhood disease, he studied physics and natural history, but ended up being devoted to the latter. Daudin wrote ' ( ...
in 1802. Louis Jean Pierre Vieillot described the genus name ''Tachypetes'' in 1816 for the
great frigatebird The great frigatebird (''Fregata minor'') is a large seabird in the frigatebird family. There are major nesting populations in the tropical Pacific (including the Galapagos Islands) and Indian Oceans, as well as a tiny population in the South At ...
. The genus name ''Atagen'' had been coined by German naturalist
Paul Möhring Paul Heinrich Gerhard Möhring (also Paul Mohr; 21 July 1710 in Jever – 28 October 1792) was a German physician, botanist and zoologist. He studied medicine in Danzig and Wittenberg, and following graduation (1733), he settled as a general pr ...
in 1752, though this has no validity as it predates the official beginning of Linnaean taxonomy. In 1874, English zoologist
Alfred Henry Garrod Alfred Henry Garrod FRS (May 18, 1846 – October 17, 1879) was an English vertebrate zoologist. Garrod was born in London, the eldest son of Sir Alfred Baring Garrod (1819–1907), a physician at King's College Hospital, who discovere ...
published a study where he had examined various groups of birds and recorded which muscles of a selected group of five they possessed or lacked. Noting that the muscle patterns were different among the steganopodes (classical
Pelecaniformes The Pelecaniformes are an order of medium-sized and large waterbirds found worldwide. As traditionally—but erroneously—defined, they encompass all birds that have feet with all four toes webbed. Hence, they were formerly also known by such ...
), 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 Procellariiformes is an order of seabirds that comprises four families: the albatrosses, the petrels and shearwaters, and two families of storm petrels. Formerly called Tubinares and still called tubenoses in English, procellariiforms are oft ...
than Pelecaniformes, though concluded they still belonged in the latter group (as suborder Fregatae), albeit as an early offshoot. Martyn Kennedy and colleagues derived a
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
based on behavioural characteristics of the traditional Pelecaniformes, calculating the frigatebirds to be more divergent than pelicans from a core group of gannets,
darters The darters, anhingas, or snakebirds are mainly tropical waterbirds in the family Anhingidae, which contains a single genus, ''Anhinga''. There are four living species, three of which are very common and widespread while the fourth is rarer and ...
and cormorants, and
tropicbirds Tropicbirds are a family, Phaethontidae, of tropical pelagic seabirds. They are the sole living representatives of the order Phaethontiformes. For many years they were considered part of the Pelecaniformes, but genetics indicates they are most cl ...
the most distant lineage. The classification of this group as the traditional Pelecaniformes, united by feet that are totipalmate (with all four toes linked by webbing) and the presence of a gular pouch, persisted until the early 1990s. The
DNA–DNA hybridization In genomics, DNA–DNA hybridization is a molecular biology technique that measures the degree of genetic similarity between pools of DNA sequences. It is usually used to determine the genetic distance between two organisms and has been used ex ...
studies of
Charles Sibley Charles Gald Sibley (August 7, 1917 – April 12, 1998) was an American ornithologist and molecular biologist. He had an immense influence on the scientific classification of birds, and the work that Sibley initiated has substantially altered our ...
and Jon Edward Ahlquist placed the frigatebirds in a lineage with
penguin Penguins ( order Sphenisciformes , family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain t ...
s, loons, petrels and
albatross Albatrosses, of the biological family Diomedeidae, are large seabirds related to the procellariids, storm petrels, and diving petrels in the order Procellariiformes (the tubenoses). They range widely in the Southern Ocean and the North Pac ...
es. Subsequent genetic studies place the frigatebirds as a sister group to the group
Suloidea The order Suliformes (, dubbed "Phalacrocoraciformes" by ''Christidis & Boles 2008'') is an order recognised by the International Ornithologist's Union. In regard to the recent evidence that the traditional Pelecaniformes is polyphyletic, it has ...
, which comprises the gannets and boobies, cormorants and darters. Microscopic analysis of eggshell structure by Konstantin Mikhailov in 1995 found that the eggshells of frigatebirds resembled those of other Pelecaniformes in having a covering of thick microglobular material over the crystalline shells. Molecular studies have consistently shown that pelicans, the namesake family of the Pelecaniformes, are actually more closely related to
heron The herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 72 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera ''Botaurus'' and ''Ixobrychu ...
s, ibises and spoonbills, the
hamerkop The hamerkop (''Scopus umbretta'') is a medium-sized wading bird. It is the only living species in the genus ''Scopus'' and the family Scopidae. The species and family was long thought to sit with the Ciconiiformes but is now placed with the ...
and the
shoebill The shoebill (''Balaeniceps rex'') also known as the whalebill, whale-headed stork or shoe-billed stork, is a very large long-legged wading bird. It derives its name from its enormous shoe-shaped bill. It has a somewhat stork-like overall form ...
than to the remaining species. In recognition of this, the
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
comprising the frigatebirds and Suloidea was renamed
Suliformes The order Suliformes (, dubbed "Phalacrocoraciformes" by ''Christidis & Boles 2008'') is an order recognised by the International Ornithologist's Union. In regard to the recent evidence that the traditional Pelecaniformes is polyphyletic, it h ...
in 2010. In 1994, the family name Fregatidae, cited as described in 1867 by French naturalists
Côme-Damien Degland Côme-Damien Degland (6 July 1787 – 1 January 1856, Lille) was a French physician and zoologist. Biography Degland was born at Armentières, and lived in Lille for most of his life, where he was the chief of the Hôpital Saint-Sauveur, and where ...
and
Zéphirin Gerbe Jean-Joseph Zéphirin Gerbe (21 December 1810 in Bras – 26 June 1890 in Bras) was a French naturalist. He was the first to discover the pattern of wing taxis, the absence (diastataxis) or presence (eutaxy) of the fifth secondary in birds. He was ...
, was conserved under Article 40(b) of the
International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the I ...
in preference to the 1840 description Tachypetidae by
Johann Friedrich von Brandt Johann Friedrich von Brandt (25 May 1802 – 15 July 1879) was a German-Russian naturalist, who worked mostly in Russia. Brandt was born in Jüterbog and educated at a gymnasium in Wittenberg and the University of Berlin. In 1831 he emigrat ...
. This was because the genus names ''Atagen'' and ''Tachypetes'' had been synonymised with ''Fregata'' before 1961, resulting in the aligning of family and genus names.


Fossil record

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 from fossil deposits in the western United States, two—''L. azygosternon'' and ''L. hasegawai''—from the
Green River Formation The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very f ...
(48–52 million years old) and one—''L. hutchisoni''—from the
Wasatch Formation The Wasatch Formation (Tw)Shroba & Scott, 2001, p.3 is an extensive highly fossiliferous geologic formation stretching across several basins in Idaho, Montana Wyoming, Utah and western Colorado. Fossil material indistinguishable from living species dating to the Pleistocene and Holocene has been recovered from
Ascension Island Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overseas Territory of ...
(for ''F. aquila''), Saint Helena Island, both in the southern Atlantic Ocean, and also from various islands in the Pacific Ocean (for ''F. minor'' and ''F. ariel''). A
cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...
study of the skeletal and bone morphology of the classical Pelecaniformes and relatives found that the frigatebirds formed a clade with ''Limnofregata''. Birds of the two genera have 15
cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sa ...
, unlike almost all other
Ciconiiformes Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family called Ciconiidae, and make up the order Ciconiiformes . Ciconiiformes previously included a number of other families, such as herons and ...
, Suliformes and Pelecaniformes, which have 17. The age of ''Limnofregata'' indicates that these lineages had separated by the Eocene.


Living species and infrageneric classification

The type species of the genus is the
Ascension frigatebird The Ascension frigatebird (''Fregata aquila'') is a seabird of the frigatebird family Fregatidae which breeds on Boatswain Bird Island and Ascension Island in the tropical Atlantic Ocean. The Ascension frigatebird is a large lightly built se ...
(''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''. In 1914 the Australian ornithologist
Gregory Mathews Gregory Macalister Mathews CBE FRSE FZS FLS (10 September 1876 – 27 March 1949) was an Australian-born amateur ornithologist who spent most of his later life in England. Life He was born in Biamble in New South Wales the son of Robert H ...
delineated five species, which remain valid. Analysis of
ribosomal Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to fo ...
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. Two subspecies of the magnificent, three subspecies of the lesser and five subspecies of the great frigatebird are recognised.


Description

Frigatebirds are large slender mostly black-plumaged seabirds, with the five species similar in appearance to each other. The largest species is the magnificent frigatebird, which reaches in length, with three of the remaining four almost as large. The lesser frigatebird is substantially smaller, at around long. Frigatebirds exhibit marked sexual dimorphism; females are larger and up to 25 percent heavier than males, and generally have white markings on their underparts. Frigatebirds have short necks and long, slender hooked bills. Their long narrow wings (male wingspan can reach ) taper to points. Their wings have eleven primary flight feathers, with the tenth the longest and eleventh a vestigial feather only, and 23 secondaries. Their tails are deeply forked, though this is not apparent unless the tail is fanned. The tail and wings give them a distinctive 'W' silhouette in flight. The legs and face are fully feathered. The totipalmate feet are short and weak, the webbing is reduced and part of each toe is free. The bones of frigatebirds are markedly
pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and ele ...
, making them very light and contributing only 5% to total body weight. The
pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of ...
is strong as its bones are fused. The pectoral muscles are well-developed, and weigh as much as the frigatebird's feathers—around half the body weight is made up equally of these muscles and feathers. 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. These can only deflate slowly, so males that are disturbed will fly off with pouches distended for some time. Frigatebirds remain in the air and do not settle on the ocean. They produce very little oil from their
uropygial gland The uropygial gland, informally known as the preen gland or the oil gland, is a bilobed sebaceous gland possessed by the majority of birds used to distribute the gland's oil through the plumage by means of preening. It is located dorsally at the ...
s so their feathers would become sodden if they settled on the surface. In addition, with their long wings relative to body size, they would have great difficulty taking off again.


Distribution and habitat

Frigatebirds are found over tropical oceans, and ride warm updrafts under
cumulus cloud Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin ''cumulo-'', meaning ''heap'' or ''pile''. Cumulus clouds are low-level clouds, gene ...
s. Their range coincides with availability of food such as flying fish, and with the
trade wind The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisph ...
s, which provide the windy conditions that facilitate their flying. They are rare vagrants to temperate regions and not found in polar latitudes. Adults are generally sedentary, remaining near the islands where they breed. However, male frigatebirds have been recorded dispersing great distances after departing a breeding colony—one male great frigatebird relocated from Europa Island in the Mozambique Channel to the Maldives away, and a male magnificent frigatebird flew from French Guiana to Trinidad. In 2015, a magnificent frigatebird was spotted as far north as Michigan. Great frigatebirds marked with wing tags on Tern Island in the French Frigate Shoals were found to regularly travel the to
Johnston Atoll Johnston Atoll is an unincorporated territory of the United States, currently administered by the United States Fish and Wildlife Service (USFWS). Johnston Atoll is a National Wildlife Refuge and part of the Pacific Remote Islands Marine Nationa ...
, although one was reported in Quezon City in the Philippines. Genetic testing seems to indicate that the species has fidelity to their site of hatching despite their high mobility. Young birds may disperse far and wide, with distances of up to recorded.


Behaviour and ecology

Having the largest wing-area-to-body-weight ratio of any bird, frigatebirds are essentially aerial. This allows them to soar continuously and only rarely flap their wings. One great frigatebird, being tracked by satellite in the Indian Ocean, stayed aloft for two months. They can fly higher than 4,000 meters in freezing conditions. Like swifts they are able to spend the night on the wing, but they will also return to an island to roost on trees or cliffs. Field observations in the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channel is about l ...
found that great frigatebirds could remain on the wing for up to 12 days while foraging. Highly adept, they use their forked tails for steering during flight and make strong deep wing-beats, though not suited to flying by sustained flapping. Frigatebirds bathe and clean themselves in flight by flying low and splashing at the water surface before preening and scratching afterwards. Conversely, frigatebirds do not swim and with their short legs cannot walk well or take off from the sea easily. According to a study in the journal ''Nature Communication'', scientists attached an
accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is accel ...
and an electroencephalogram testing device on nine great frigatebirds to measure if they slept during flight. The study found the birds do sleep, but usually only using one hemisphere of the brain at a time and usually sleep while ascending at higher altitudes. The amount of time mid-air sleeping was less than an hour and always at night. The average life span is unknown but in common with seabirds such as the wandering albatross and
Leach's storm petrel Leach's storm petrel or Leach's petrel (''Hydrobates leucorhous'') is a small seabird of the tubenose order. It is named after the British zoologist William Elford Leach. The scientific name is derived from Ancient Greek. ''Hydrobates'' is from ...
, 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. Despite having dark plumage in a tropical climate, frigatebirds have found ways not to overheat—particularly as they are exposed to full sunlight when on the nest. They ruffle feathers to lift them away from the skin and improve air circulation, and can extend and upturn their wings to expose the hot undersurface to the air and lose heat by evaporation and convection. Frigatebirds also place their heads in the shade of their wings, and males frequently flutter their gular pouches.


Breeding behaviour

Frigatebirds typically breed on remote oceanic islands, generally in colonies of up to 5000 birds. Within these colonies, they most often nest in groups of 10 to 30 (or rarely 100) individuals. Breeding can occur at any time of year, often prompted by commencement of the dry season or plentiful food. Frigatebirds have the most elaborate mating displays of all seabirds. The male birds take up residence in the colony in groups of up to thirty individuals. They display to females flying overhead by pointing their bills upwards, inflating their red throat pouches and vibrating their outstretched wings, showing the lighter wing undersurfaces in the process. They produce a drumming sound by vibrating their bills together and sometimes give a whistling call. The female descends to join a male she has chosen and allows him to take her bill in his. The pair also engages in mutual "head-snaking". After copulation it is generally the male who gathers sticks and the female that constructs the loosely woven nest. The nest is subsequently covered with (and cemented by)
guano Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. ...
. Frigatebirds prefer to nest in trees or bushes, though when these are not available they will nest on the ground. A single white egg that weighs up to 6–7% of mother's body mass is laid, and is incubated in turns by both birds for 41 to 55 days. The
altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
chicks are naked on hatching and develop a white down. They are continuously 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, after which the male's attendance trails off leaving the mother to feed the young for another six to nine months on average. The chicks feed by reaching their heads in their parents' throat and eating the part-regurgitated food. It takes so long to rear a chick that frigatebirds generally breed every other year. 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 ten to eleven years of age.


Feeding

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, particularly the genera ''
Exocoetus ''Exocoetus'' is a genus of flying fishes. It is a bony fish. The body is covered with cycloid scales. The mouth is wide, and the jaws bear teeth. It is a marine fish. The tail has hypobatic fins as the ventral lobe. Species Five species in thi ...
'' and '' Cypselurus'', that are driven to the surface by predators such as tuna and
dolphinfish ''Coryphaena'' is a genus of marine ray-finned fishes known as the dolphinfishes, and is currently the only known genus in the family Coryphaenidae. The generic name is from Greek κορυφή (''koryphē'', "crown, top") and -αινα (-''ain ...
, but they will also eat
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, a ...
s, particularly squid. Menhaden of the genus ''
Brevoortia Menhaden, also known as mossbunker and bunker and "the most important fish in the sea", are forage fish of the genera ''Brevoortia'' and ''Ethmidium'', two genera of marine fish in the family Clupeidae. ''Menhaden'' is a blend of ''poghaden' ...
'' can be an important prey item where common, and jellyfish and larger plankton are also eaten. Frigatebirds have learned to follow fishing vessels and take fish from holding areas. Conversely tuna fishermen fish in areas where they catch sight of frigatebirds due to their association with large marine predators. Frigatebirds also at times prey directly on eggs and young of other seabirds, including boobies, petrels, shearwaters and terns, in particular the sooty tern. Frigatebirds will rob other
seabird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same envir ...
s such as boobies, particularly the
red-footed booby The red-footed booby (''Sula sula'') is a large seabird of the booby family, Sulidae. Adults always have red feet, but the colour of the plumage varies. They are powerful and agile fliers, but they are clumsy in takeoffs and landings. They are f ...
,
tropicbird Tropicbirds are a family, Phaethontidae, of tropical pelagic seabirds. They are the sole living representatives of the order Phaethontiformes. For many years they were considered part of the Pelecaniformes, but genetics indicates they are most c ...
s, shearwaters, petrels, terns, gulls and even
osprey The osprey (''Pandion haliaetus''), , also called sea hawk, river hawk, and fish hawk, is a diurnal, fish-eating bird of prey with a cosmopolitan range. It is a large raptor reaching more than in length and across the wings. It is brown o ...
s of their catch, using their speed and manoeuvrability to outrun and harass their victims until they regurgitate their stomach contents. They may either assail their targets after they have caught their food or circle high over seabird colonies waiting for parent birds to return laden with food. 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%. Unlike most other seabirds, frigatebirds drink freshwater when they come across it, by swooping down and gulping with their bills.


Parasites

Frigatebirds are unusual among seabirds in that they often carry blood parasites. Blood-borne
protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
of the genus ''
Haemoproteus ''Haemoproteus'' is a genus of alveolates that are parasitic in birds, reptiles and amphibians. Its name is derived from Greek: ''Haima'', "blood", and ''Proteus'', a sea god who had the power of assuming different shapes. The name ''Haemoproteu ...
'' have been recovered from four of the five species. Bird lice of the ischnoceran genus '' Pectinopygus'' and amblyceran genus '' Colpocephalum'' and species '' Fregatiella aurifasciata'' have been recovered from magnificent and great frigatebirds of the Galapagos Islands. Frigatebirds tended to have more parasitic lice than did boobies analysed in the same study. A heavy chick mortality at a large and important colony of the magnificent frigatebird, located on Île du Grand Connétable off French Guiana, was recorded in summer 2005. Chicks showed nodular skin lesions, feather loss and corneal changes, with around half the year's progeny perishing across the colony. An
alphaherpesvirus ''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπειν ...
was isolated and provisionally named ''Fregata magnificens'' herpesvirus, though it was unclear whether it caused the outbreak or affected birds already suffering malnutrition.


Status and conservation


Populations and threats

Two of the five species are considered at risk. In 2003, a survey of the four colonies of the critically endangered Christmas Island frigatebirds counted 1200 breeding pairs. As frigatebirds normally breed every other year, the total adult population was estimated to lie between 1800 and 3600 pairs. Larger numbers formerly bred on the island, but the clearance of breeding habitat during World War II and dust pollution from phosphate mining have contributed to the decrease. The population of the vulnerable Ascension frigatebird has been estimated at around 12,500 individuals. The birds formerly bred on Ascension Island itself, but the colonies were exterminated by
feral cat A feral cat or a stray cat is an unowned domestic cat (''Felis catus'') that lives outdoors and avoids human contact: it does not allow itself to be handled or touched, and usually remains hidden from humans. Feral cats may breed over dozens ...
s introduced in 1815. The birds continued to breed on a rocky outcrop just off the shore of the island. A program conducted between 2002 and 2004 eradicated the feral cats and a few birds have returned to nest on the island. The other three species are classified by the
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
as being of ''Least Concern''. The populations of all three are large, with that of the magnificent frigatebird thought to be increasing, while the great and lesser frigatebird decreasing. Monitoring populations of all species is difficult due to their movements across the open ocean and low reproductivity. The status of the Atlantic populations of the great and lesser frigatebirds are unknown and possibly extinct. As frigatebirds rely on large marine predators such as tuna for their prey, overfishing threatens to significantly impact on food availability and jeopardise whole populations. As frigatebirds nest in large dense colonies in small areas, they are vulnerable to local disasters that could wipe out the rare species or significantly impact the widespread ones.


Hunting

In
Nauru Nauru ( or ; na, Naoero), officially the Republic of Nauru ( na, Repubrikin Naoero) and formerly known as Pleasant Island, is an island country and microstate in Oceania, in the Central Pacific. Its nearest neighbour is Banaba Island in Kir ...
, catching frigatebirds was an important tradition still practised to some 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 icit to ground." Marine birds including frigatebirds were once harvested for food on Christmas Island but this practice ceased in the late 1970s. Eggs and young of magnificent frigatebirds were taken and eaten in the Caribbean. Great frigatebirds were eaten in the Hawaiian Islands and their feathers used for decoration.


Cultural significance

The frigate bird appears on the national
Flag of Kiribati The flag of Kiribati (Gilbertese: ''buraki ni Kiribati'') is red in the upper half with a gold frigatebird ( ''Fregata minor'', in Gilbertese: ''te eitei'') flying over a gold rising sun (''otintaai''), and the lower half is blue with three hori ...
. The design is based on its former colonial Gilbert and Ellice Islands coat of arms. The bird also appears on the flag of
Barbuda Barbuda (), is an island located in the eastern Caribbean forming part of the sovereign state of Antigua and Barbuda. It is located north of the island of Antigua and is part of the Leeward Islands of the West Indies. The island is a popular ...
, and is the national bird of
Antigua and Barbuda Antigua and Barbuda (, ) is a sovereign country in the West Indies. It lies at the juncture of the Caribbean Sea and the Atlantic Ocean in the Leeward Islands part of the Lesser Antilles, at 17°N latitude. The country consists of two majo ...
. There are anecdotal reports of tame frigatebirds being kept across Polynesia and Micronesia in the Pacific. A bird that had come from one island and had been taken elsewhere could be reliably trusted to return to its original home, hence would be used as a speedy way to relay a message there. There is evidence of this practice taking place in the Gilbert Islands and Tuvalu. The great frigatebird was venerated by the
Rapa Nui people The Rapa Nui (Rapa Nui: , Spanish: ) are the Polynesian peoples indigenous to Easter Island. The easternmost Polynesian culture, the descendants of the original people of Easter Island make up about 60% of the current Easter Island population an ...
on
Easter Island Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is most famous for its nearly ...
; carvings of the birdman
Tangata manu The ''Tangata manu'' ("bird-man," from "human beings" + "bird") was the winner of a traditional competition on Rapa Nui (Easter Island). The ritual was an annual competition to collect the first sooty tern () egg of the season from the islet of ...
depict him with the characteristic hooked beak and throat pouch. Its incorporation into local ceremonies suggests that the now-vanished species was extant there between the 1800s and 1860s. Maritime folklore around the time of European contact with the Americas held that frigatebirds were birds of good omen as their presence meant land was near.


See also

*
List of birds by flight speed This is a list of the fastest flying birds in the world. A bird's velocity is necessarily variable; a hunting bird will reach much greater speeds while diving to catch prey than when flying horizontally. The bird that can achieve the greatest airs ...


Explanatory notes


References


External links


Frigatebird videos, photos and sounds
on the Internet Bird Collection {{Authority control
Fregatidae Frigatebirds are a family of seabirds called Fregatidae which are found across all tropical and subtropical oceans. The five extant species are classified in a single genus, ''Fregata''. All have predominantly black plumage, long, deeply forked ...
Extant Ypresian first appearances Pleistocene animals of Africa Pleistocene animals of Asia Pleistocene animals of Oceania Pleistocene animals of South America Pleistocene birds of North America Pleistocene birds Seabirds Taxa named by Bernard Germain de Lacépède