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Frigatebirds (Fregatidae)

Frigatebirds

(Fregatidae)

Class Aves

Order Pelecaniformes

Suborder Pelecani

Family Fregatidae


Thumbnail description
Distinctive, dark-colored seabirds with extremely long and pointed wings, and a forked tail. Gular (throat) region is unfeathered, expanded, and colorful in breeding males. Plumage is largely black or dark brown. Bill is long and strongly hooked; nostrils absent. Middle claw is pectinate (serrated or bears projections like the teeth of a comb), and feet are webbed. Possess the lightest wing-loading of any species, giving them great flying and soaring skills

Size
Body length is 30–44 in (75–112 cm) and wingspread 69–91 in (176–230 cm); females larger

Number of genera, species
1 genus; 5 species

Habitat
Coastal waters of tropical and subtropical oceans of most of the world

Conservation status
The Christmas frigatebird (Fregata andrewsi) and the Ascension Island frigatebird (F. aquila) are listed as Critically Endangered

Distribution
Breed on isolated tropical islands and tend to remain fairly local to those places when feeding and during the nonbreeding season; the genus ranges worldwide in tropical and subtropical coastal waters

Evolution and systematics

The five species of frigatebirds (genus Fregata) are the only ones in the family Fregatidae. They are related to the pelicans, tropicbirds, cormorants, and gannets, which are also water birds in the order Pelecaniformes (characterized by four toes connected by webs, plus other traits). The Pelecaniformes lineage is ancient, with a fossil record extending to the Lower Eocene (more than 54 million years ago). The five species of Fregatidae are: the magnificent frigatebird (F. magnificens), the Ascension Island frigatebird (F. aquila), the Christmas frigatebird (F. andrewsi), the lesser frigatebird (F. ariel), and the great frigatebird (F. minor). A fossil frigatebird has been recovered from a deposit in England from the Lower Eocene.

Physical characteristics

Frigatebirds have a body length of 30–44 in (75–112 cm), a wingspan of 69–91 in (176–230 cm), and a weight up to 3.3 lb (1.5 kg). They have long, sweeping, narrow wings, in which the lower arm and hand bones are strongly elongated. Almost half of their body weight consists of breast muscles and feathers, and the loading per unit of wing surface area is extremely small (proportionately to their body weight, they have the largest wings of any bird). This anatomical design allows frigatebirds to be excellent fliers and extremely efficient at soaring on rising columns of warm air. They can fly faster than 30 mph (48 kph). The tail is deeply forked and is often spread and then closed again in flight, acting as a rudder to steer the bird. The legs are short, and the small feet have only rudimentary webbing between the base of the rather short toes. The bill is long and bent into a strong hook at the tip. The gular region is nonfeathered. Females are somewhat larger than males and are marked differently, with a white throat rather than the inflatable red sac of the adult male. The body plumage is colored mostly glossy-black, with some white markings, especially on females. Young have a white head and breast.

Distribution

Frigatebirds range widely in coastal waters of tropical and subtropical regions of the world. They breed on isolated tropical islands, such as Christmas Island in the Indian Ocean, Ascension Island in the south Atlantic, and the Hawaiian Islands in the Pacific. The magnificent frigatebird is relatively widespread, but the other four species are all endemics—rare,

locally evolved species that only breed on a few highly remote, oceanic islands.

Habitat

Frigatebirds breed on isolated tropical islands and forage in coastal waters of tropical and subtropical oceans, usually fairly close to their breeding sites. They occur mainly where flying fish (Hirundichthys) are abundant and in regions with water of at least about 77°F (25°C).

Behavior

Frigatebirds sometimes steal food from other seabirds by harassing them relentlessly until they disgorge any fish in their gullet. The frigatebirds then scoop up such bounty as it falls through the air. This unusual, thieving behavior is known as kleptoparasitism. Frigatebirds almost never swim, as their plumage is only lightly oiled and quickly becomes wet and heavy. They are excellent fliers and can stay aloft during strong winds with little effort. Upon landing, their very long wings can be a hindrance; this along with their short legs and tiny feet makes it awkward for them to land, perch, or walk. They often have problems when landing on their nest, particularly if strong winds are blowing. Frigatebirds tend to breed year-round and to stay near their home islands. However, they are known to sometimes fly far out over the ocean, and wander extensively when not breeding. Frigatebirds can be noisy around their nesting sites but are silent when at sea.

Feeding ecology and diet

Flying fish are a principal food of frigatebirds. They are caught in the air up to 6 or more feet (several meters) above the surface of the ocean. Frigatebirds also eat other small species of fish, as well as jellyfish, marine crustaceans, and young turtles. These foods are snatched adeptly from the surface of the water. They also eat carrion (including offal and by-catch discarded by fishing boats), eggs, and the chicks of other species of seabirds. Frigatebirds sometimes chase boobies and other marine birds, pestering them so relentlessly that they regurgitate their recently caught food in order to escape the harassment. The disgorged meal is skillfully caught by the frigatebird in the air and eaten. They take young seabirds from the ground or water surface by diving down and grabbing them with their hooked beak while in flight.

Reproductive biology

Frigatebirds may breed at any time of the year. They usually build a nest in a low shrub or tree or sometimes on the ground. The nest is a flimsy-looking, flat platform made of interworked twigs, sticks, grasses, and reeds. They nest in colonies, which are usually close to those of other seabirds, particularly cormorants, gannets, pelicans, or terns. Frigatebirds often rob these other birds of their prey and sometimes feed on their young. During courtship, male frigatebirds use their inflatable, bright-red throat sac in a balloon-like display to impress eligible females. While trying to attract a mate, a male frigatebird occupies a suitable nesting site in the colony and shows off his outspread, glossy-black wings and inflated throat sac to any females flying above. If an interested partner approaches, the male shakes himself and conspicuously rattles his bill and wings. Frigatebirds are monogamous during each breeding attempt, but do not remain together after breeding or reunite for future attempts. Like most seabirds, frigatebirds lay only a single white egg. The egg weighs about 6% of the mother's body weight. Both parents incubate the egg over a period of 40–50 days. The young bird is naked when hatched and is fed by regurgitation by both parents. The young frigatebird is fully feathered in about 140 days and stays in the nest for a total of four to five months. The first attempt at flight occurs around 149–207 days after hatching. The fledgling depends on its parents for food for another two to six months. The young also fly about the colony in small groups and feed on scraps of food they find. Playing high in the air with feathers and bits of seaweed, young frigatebirds exercise their flight muscles and practice the techniques necessary for the highly skilled flight of adults. Frigatebirds become sexually mature at 5–7 years.

Conservation status

The Christmas frigatebird and the Ascension Island frigatebird are listed as Critically Endangered by the IUCN. Both of these extremely rare species have suffered greatly from destruction of their breeding habitat and from predation and habitat damage caused by introduced animals.

Significance to humans

Frigatebirds are not of much direct importance to humans, except for the economic benefits of tourism related to birdwatching and ecotourism. However, their ability to navigate is strong enough that these birds have been used in the past by local people to send messages between remote South Pacific islands, in the manner that carrier pigeons are used elsewhere in the world.

Species accounts

List of Species

Magnificent frigatebird
Christmas frigatebird
Ascension frigatebird

Magnificent frigatebird

Fregata magnificens

taxonomy

Fregata magnificens Mathews, 1914, Barrington Island, Galápagos.

other common names

English: Magnificent frigatebird; French: Frégate superbe; German: Prachtfregattvogel; Spanish: Rabihorcato Magnífico.

physical characteristics

This is the largest frigatebird, with a body length of 41–44 in (103–112 cm), a wing span of 91 in (230 cm), and weight of 3.1–3.3 lb (1.4–1.5 kg). The female has a white breast and head and brownish upper-wing coverts, while the male has a mostly black body, with some white on the chest and a prominent red throat sac that is greatly inflated during sexual display.

distribution

Occurs in tropical and subtropical waters of the Atlantic and Pacific Oceans of the Americas. Breeds as far west as the Galápagos Islands.

habitat

Inhabits tropical and subtropical coastal waters, often near mangrove forest.

behavior

Outstanding fliers, they often soar to great heights. They are silent at sea but may be noisy at the breeding colony, where they make harsh, guttural notes during courtship.

feeding ecology and diet

Feed on flying fish skillfully caught in the air, on other small fish, and on squid and other marine animals snatched at the sea's surface. They also feed on fishery offal and discarded by-catch and may predate the eggs and young of other seabirds. In addition, they feed on meals that other seabirds are harassed into disgorging in flight.

reproductive biology

Females lay a single egg in a low nest, usually built in a mangrove tree or shrub. The egg is incubated by both parents for about 50 days. The chick is naked when born but fully feathered at around 140 days. It is fed regurgitated food by both parents. First flight occurs around 149–207 days after hatching. Sexual maturity is at 5–7 years.

conservation status

Not threatened. Some local populations are declining because of disturbance or destruction of nesting sites and declines of food abundance caused by overfishing, but the species overall is not considered at risk.

significance to humans

Not of much importance to people, except for the economic benefits of ecotourism related to birdwatching.


Christmas frigatebird

Fregata andrewsi

taxonomy

Fregata andrewsi Mathews, 1914, Christmas Island.

other common names

English: Christmas Island frigatebird, Andrews' frigatebird; French: Frégate d'Andrews; German: Weissbrauch Fregattvogel; Spanish: Rabihorcado Grande.

physical characteristics

Body length of 35–39 in (89–100 cm), a wingspan of 81–90 in (206–230 cm), and weight of about 2.6 lb (1.2 kg). Males and females have a white belly and a brown wing band. Females have a black throat, while males have a bright red, inflatable throat sac used in courtship displays.

distribution

Breeds on Christmas Island in the Indian Ocean but may feed more widely in tropical and subtropical coastal waters of the eastern Indian and southwestern Pacific Oceans.

habitat

Inhabits tropical and subtropical coastal waters, often near mangrove forest.

behavior

Like other frigatebirds, they are outstanding fliers, often soaring to impressive heights. They are silent at sea but noisy at their breeding colony.

feeding ecology and diet

Feed on flying fish caught in the air, on other small fish, squid, and other marine food snatched at the sea's surface, and on meals they force other seabirds to disgorge in flight. They also feed on fishery offal and by-catch and predate the eggs and young of other seabirds.

reproductive biology

Lays a single egg in a low nest, usually built in a mangrove tree or shrub. The egg is incubated by both parents. The chick is naked when born and is fed by both parents. Sexual maturity is at 5–7 years.

conservation status

This species is listed as Critically Endangered because it breeds on only one tiny island, where its small and rapidly decreasing population is threatened by poaching, habitat destruction by mining and settlement, and an introduced ant species.

significance to humans

Not of much importance to people, except for the economic benefits of ecotourism related to birdwatching.


Ascension frigatebird

Fregata aquila

taxonomy

Fregata aquilia Linnaeus, 1758, Ascension Island.

other common names

English: Ascension Island frigatebird; French: Frégate aigle-demer; German: Adlerfregattvogel; Spanish: Rabihorcado de Ascensión.

physical characteristics

Body length of 35–38 in (89–96 cm), a wingspan of 77–79 in (196–201 cm), and a weight of about 2.6 lb (1.2 kg). Males have a greenish gloss on their black plumage, while females are brownish on the upper breast, nape, and wing band. The male has a bright red, inflatable throat sac used during courtship.

distribution

Breeds on Ascension Island in the south Atlantic Ocean. It mostly occurs near the breeding island but may also feed more widely in waters of the south Atlantic.

habitat

Inhabits tropical and subtropical coastal waters, often near mangrove forest.

behavior

Outstanding fliers, they often soar to great heights. They are silent at sea but noisy at the breeding colony.

feeding ecology and diet

Feed on flying fish caught in the air, on other small fish, squid, and other marine food snatched at the sea's surface and on meals they force other seabirds to disgorge in flight. They also feed on fishery offal and by-catch and predate the eggs and young of other seabirds.

reproductive biology

Lay a single egg in a low nest, usually built in a mangrove tree or shrub. The egg is incubated by both parents. The chick is naked when born and is fed by both parents. Sexual maturity is at 5–7 years.

conservation status

This species is considered Critically Endangered because it breeds on only one tiny island, where its small and decreasing population is severely threatened by predation by introduced feral cats. It may also be at risk because of food depletion caused by fishing activities in its feeding habitat.

significance to humans

Not of much importance to people, except for the economic benefits of ecotourism related to birdwatching.


Resources

Books

BirdLife International. Threatened Birds of the World. Barcelona: Lynx Edicions; and Cambridge, United Kingdom: BirdLife International, 2000.

Harrison, P. Seabirds. An Identification Guide. Beckenham, United Kingdom: Croom Helm Ltd., 1983.

Orta, J. "Family Fregatidae (Frigatebirds)." In Vol. 1 of Handbook of the Birds of the World, edited by J. del Hoyo, A. Elliott, and J. Sargatal. Barcelona: Lynx Edicions, 1992.

Organizations

BirdLife International. Wellbrook Court, Girton Road, Cambridge, Cambridgeshire CB3 0NA United Kingdom. Phone: +44 1 223 277 318. Fax: +44-1-223-277-200. E-mail: [email protected] Web site: <http://www.birdlife.net>

IUCN–The World Conservation Union. Rue Mauverney 28, Gland, 1196 Switzerland. Phone: +41-22-999-0001. Fax: +41-22-999-0025. E-mail: [email protected] Web site: <http://www.iucn.org>

Other

Frigatebirds. Jan. 2002. Department of Ecology and Evolutionary Biology, Cornell University. 29 Jan. 2002. <http://www.eeb.cornell.edu/winkler/botw/fregatidae.html>

Fregatidae: Magnificent frigatebird. Jan. 2002. Florida Ecosystems. 29 Jan. 2002. <http://www.floridaecosystems.org/fregatidae.htm>

Bill Freedman, PhD

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