Lesser frigatebird (Fregata ariel)
|Also known as:||Least frigatebird, lesser frigata, lesser frigate, lesser frigate bird|
|Size||Length: 71 – 81 cm (2)|
Wingspan: 175 – 193 cm (2)
Male weight: 625 – 875 g (2)
Female weight: 760 – 955 g (2)
Classified as Least Concern (LC) on the IUCN Red List (1).
With their distinctive angular, pointed wings and long, scissor-shaped tails, the frigatebirds are perhaps the most recognisable of all seabirds (3). Frigatebirds have the largest wing area to body mass ratio of any bird, making them perfectly designed for an aerial lifestyle, and with their massive wingspan, these birds are able to soar almost effortlessly and make spectacular manoeuvres (3) (4). Frigatebirds are also the only seabird family that display obvious, significant differences in plumage between the sexes. The male lesser frigatebird is all black, except for a white patch under the wings that extends onto the side of the breast. They have a glossy blue, purple and green sheen to the feathers of the head, neck and upper back region, and, like other male frigatebirds, possess a large, red gular pouch that is blown up like a balloon during displays to attract a mate (2) (3). The female is larger than the male, has a less glossy sheen to the black feathers, has a gular pouch that is not distensible and a white upper breast, with the white extending onto the sides. The juvenile has a reddish-brown head and upper neck and white undersides, and displays a number of immature plumages before eventually taking on that of the adult (2). While perfectly adapted for magnificent flight manoeuvres, the lesser frigatebird is less impressive on land and sea (3). It has short legs and very small feet, making movements on land quite awkward, while the plumage lacks a waterproof coating and the feet are un-webbed, meaning this bird spends no time on the water. If it sits on the water for more than a minute or two it has great difficulty getting into the air owing to wet plumage (3) (4).
The lesser frigatebird is a widespread seabird, with major colonies in the Indian Ocean, West and Central Pacific and Southern Atlantic, where a single population resides on the remote Brazilian islands of Trindade and possibly also Martin Vaz. During the breeding season, adult birds usually stay within 100 to 200 kilometres of the colony, but when not breeding, they range widely throughout tropical seas (2) (5) (6). There are three distinct subspecies of the lesser frigatebird: Fregata ariel ariel is found in the Central and Eastern Indian Ocean and the West and Central Pacific Ocean, F. a. iredalei is found in the Western Indian Ocean, and F. a. trinitatis in the Southern Atlantic (2).
The lesser frigatebird inhabits remote islands in tropical and sub-tropical seas, where it breeds in small bushes, mangroves and even on the ground (2) (5).
Frigatebirds are remarkable for being capable of staying in flight for several days and nights, and may even sleep while on the wing. Like other frigatebirds, this species uses thermals to soar to heights of up to 2,500 metres, gliding downwards and climbing again in succession, with little need for wing flapping. This effortless flight allows long distances to be covered with minimal energetic cost (4).
The lack of waterproof plumage means that this species obtains most of its prey either just above, floating on, or submerged a few centimetres below the water surface. As such, its main source of prey is flying fish (airborne or just beneath the surface), but it also takes squid, jellyfish and scraps discarded by boats, and will often feed over tuna and other predatory fish that drive smaller fish species to the surface (2) (3). In addition to catching prey, the lesser frigatebird will sometimes harass other bird species on the wing, forcing them to release food that they have recently caught, which is then snatched from mid-air before it reaches the water (2) (3). When not airborne, the lesser frigatebird perches in trees, bushes or, less preferably, on the ground. A gregarious species, roosting takes place in large groups, where, during the day, individuals may display a remarkable sunning posture, involving sitting upright with the wing undersides rotated upwards while extended to the sides, exposing the chest and underwings to the sun (3).
The breeding behaviour of the lesser frigatebird is highly unusual and dramatic. During courtship, males gather in groups of various sizes, with gular pouches inflated, bills clattering, and wings and heads waving, while calling to attract females flying overhead. Once a pair decides to mate, they snake necks together and nibble at each others feathers, before commencing the construction of a nest. The male provides material such as twigs, while the female does the actual building. Both birds defend the nest from intruders or theft of nesting material by other males (3). After mating, a single white egg is laid, which is incubated for around 46 days by both the male and female. The chick, which takes 20 to 24 weeks to fledge from the nest, is tended to and fed by both sexes for a further four to six months (2). This extended period of parental care exhibited by all frigatebirds is the longest of all birds, and means that a pair can only breed in alternate years. However, despite this intense level of parent care, many chicks starve to death within months of becoming fully independent because they do not learn to feed themselves (3). Furthermore, some areas in which the lesser frigatebird nests are severely affected by the occurrance of El Niño evnts, during which many young starve to death as the local fish move elsewhere and good fishing skills become even more important (6).
With its large range and population, estimated at more than 200,000 individuals, the lesser frigatebird is not currently considered at risk of extinction (5). However, this species is in decline in some areas, most likely due to a combination of habitat destruction, disturbance and direct persecution by humans for food. This decline has been most notable within the Southern Atlantic population, which disappeared from St Helena, and possibly also Martin Vaz, and may now be restricted to just the single island of Trindade. The Central Pacific population is also potentially threatened by severe weather events caused by El Niño events which can cause partial or total breeding failure (2). Any threats to the lesser frigatebird are compounded by its very slow reproductive rate, and a large drop in a population may go unnoticed for several years due to its long lifespan (3).
Although this bird is considered protected on many small island countries across its range, there is often very little enforcement of such protective legislation (6). The lesser frigatebird would also benefit from a population assessment throughout its range, and further research into the threats to its survival (2).
For more information on the lesser frigatebird, see:
Authenticated (05/08/2010) by Dr. E. A. Schreiber, Research Associate, Bird Department of the Smithsonian National Museum of Natural History.
- El Niño: a natural phenomenon that happens every 4 to 12 years, and lasts for several months, when upwelling of cold, nutrient-rich water does not occur. This causes the warming of ocean surface water off the western coast of South America and causes die-offs of plankton and fish. It also affects Pacific jet stream winds, altering storm tracks and creating unusual weather patterns in various parts of the world.
- Gular pouch: a large distensible pouch below the beak of some birds.
- Incubate: to keep eggs warm so that development is possible.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Thermals: masses of heated air which rise to several thousand feet, and may be used by birds, insects and man to gain altitude and exploit higher altitude winds.
IUCN Red List (June, 2010)
- del Hoyo, J., Elliott, A. and Sargatal, J. (2001) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
- Perrins, C. (2009) The Encyclopedia of Birds. Oxford University Press, Oxford.
- Weimerskirch, H., Chastel, O., Barbraud, C. and Tostain, O. (2003) Frigatebirds ride high on thermals. Nature, 421: 333-334.
BirdLife International (June, 2010)
- Schreiber, E.A. (2010) Pers. comm.