White-bellied frigate bird

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White-bellied frigate bird
young white-bellied frigate bird (Fregata andrewsi)

young white-bellied frigate bird ( Fregata andrewsi )

Systematics
Class : Birds (aves)
Order : Suliformes
Family : Frigate birds (Fregatidae)
Genre : Frigate birds ( Fregata )
Type : White-bellied frigate bird
Scientific name
Fregata Andrewsi
Mathews , 1914

The white-bellied frigate bird ( Fregata andrewsi ) is a rare sea bird that breeds on Christmas Island . In the Red List of Threatened Species of the IUCN , the species is listed in the category “critically endangered”. The IUCN estimates the population at currently 2,400 to 4,800 sexually mature individuals.

description

The white-bellied frigate bird reaches a length of 90 to 100 cm and a wingspan of 250 cm. The color of its plumage is predominantly black with a greenish tinge. The throat, neck and chest are black with a purple tinge. The tail is strongly forked. The belly is white and the upper wings are lightly banded. The male has a red throat pouch and a long, dark gray curved beak. The head of the adult females is black. A white collar extends from the throat over the chest area to the armpits. The belly is white and the beak is pink. The young birds are black-brown on the top and yellow-brown on the head and underside. Some young birds have dark stripes on their chests.

There is a possibility of confusion with the other frigate birds. The similarity with the banded frigate bird and the ariel frigate bird is particularly pronounced . Both species are smaller and lighter than the white-bellied frigate bird. Ariel frigate birds also have a narrow white stripe on the underside of the body on both sides of the belly. The white frigate bird, however, is completely black on the underside. The white-bellied frigate bird, on the other hand, has a white spot on the lower half of the abdomen. Young birds of the three species, however, can hardly be distinguished.

Distribution area

Map of Christmas Island, the only location of breeding colonies of the white-bellied frigate bird

The white-bellied frigate bird is an endemic breeding bird of Christmas Island. Here it breeds in a 2 km² area in the Christmas Island National Park. There were also documented sightings on the Indonesian Java , Timor , Lombok , Semau as well as Malaysia , Thailand and northern Australia . While foraging for food, the white-bellied frigate bird is confined exclusively to tropical waters of the Indian Ocean. There is evidence that he prefers regions of the Indian Ocean that have a surface temperature of more than 26.4 degrees Celsius. During their migration, white-bellied frigate birds reach a region that extends from the waters of Indonesia to the South China Sea, the Andaman Sea, the Sulu Sea and the Gulf of Thailand.

Way of life

Like all other frigate birds, the white-bellied frigate bird can swim and run very poorly. His legs are too weak for that. It only comes ashore at night and during the breeding season and can hold onto the branches with its claws. Thanks to its strong wings and long forked tail, it can spend most of the day above the sea. They live in groups and prey on flying fish and octopus or they aggressively rob other sea birds such as boobies, gulls, pelicans and cormorants of their food. Here the birds are pushed with their long wings and attacked with their beaks until the robbed birds choke up their food and this is then caught by the frigate birds.

White-bellied frigate birds are monogamous, the pairing relationship probably does not last longer than one reproductive period. The age at which the white-bellied frigate birds first brood has not been studied precisely. Presumably, however, they breed for the first time when they are five years old. They are colony breeders who build their nests in tall trees that protrude above the rest of the vegetation. Within the colony, sub-colonies with ten to twenty nests can be distinguished. There are between three and ten nests in the individual trees. The distance between the individual nests is occasionally less than a meter. The nest is very small and consists of twigs. The nesting material is brought in by the male and built in by the female. The nest building begins very early in the mating phase and the nest is largely built within ten days. However, the females keep mending the nests until the chick hatches. In general, one of the two partner birds always stays at the nest location after mating.

The males begin courtship at the end of December. Around 90 percent of the eggs in a year are laid between March and mid-May. The breeding season is between 50 and 54 days. Both parent birds breed, but the breeding intervals of the female are slightly longer. The only egg that makes up the clutch is elliptical, white in color and has a smooth shell. If the clutch is lost, additional clutch can occur. At birth the chick is totally naked and only later does the fluff grow. The parent birds hover and guard the chick for about six weeks. After four months the young birds have reached the plumage color of the adults and after seven months they are independent.

The breeding success is not very high and is estimated at around thirty percent. In one study, 67 chicks hatched from 84 eggs, 46 fledglings fledged and of these, only 24 reached the age at which they became independent from their parent birds. Nine nests with eggs were destroyed by storms and five clutches were abandoned. Among them were two clutches where the partner bird did not return to the nesting site. The 17th egg was lost when an unmated male occupied the nest. Twelve of the chicks died in the first few weeks after hatching, three more died of starvation because one of the parent birds did not return to the nest and one died because an unmated male conquered the nest. The rest were abandoned by the parent birds for no apparent reason. Three of the nestlings died in storms, the rest either disappeared or starved to death. Based on the investigations, it was concluded that lack of food is the decisive factor that contributes to the low breeding success of the white-bellied frigate birds.

Danger

The white-bellied frigate bird is one of the rarest sea birds in the world. As an endemic species whose breeding grounds are on only one island and there in a few breeding colonies, the white-bellied frigate bird is generally exposed to a population collapse due to extraordinary events such as epidemics or extreme weather conditions, which can be of an extent that the survival of the species endangered. In addition, the reproduction rate of the white-bellied frigate birds is very low.

The previous hunt for this species has ceased in the 1980s. The main threats are habitat degradation, air pollution from phosphate mining, and commercial fishing in the waters where white-bellied frigate birds hunt for food. The phosphate mining on Christmas Island has led to forested areas where the frigate birds were resting and breeding colonies were cut down. In addition, white-bellied frigate birds do not breed in the places where the dust that is created during drying phosphate accumulates on plants.

At the beginning of the 1990s the yellow spinner ant was introduced to Christmas Island , which does not pose a direct threat to the white-bellied frigate bird, but leads to far-reaching changes in the habitat on this single breeding island and in the medium term endangers the breeding colonies of this species.

It is generally assumed that the population has decreased by about 66 percent over the last three generations. It is assumed that this decline will continue.

Worth mentioning

This species is one of the marathon flyers among the sea birds. In 2005, the female Lydia was tagged with a satellite transmitter and the scientists were able to follow a non-stop flight of 26 days. The flight went 4000 km from Christmas Island via Sumatra, Java, Borneo back to Christmas Island, where her cub was waiting for her. The scientists found that Lydia did not make a stopover, but instead fed on the sea and slept while flying.

supporting documents

literature

  • Josep del Hoyo : Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona 1992, ISBN 8487334105 .
  • PJ Higgins (Ed.): Handbook of Australian, New Zealand & Antarctic Birds , Volume 1, Ratites to Ducks, Oxford University Press, Oxford 1990, ISBN 0195530683

Single receipts

  1. ↑ BirdLife factsheet on the white-bellied frigate bird , accessed May 17, 2011
  2. ^ Higgins, p. 928
  3. ^ Higgins, p. 929
  4. ^ Colin Trainor: First record of the Christmas Island Frigatebird Fregata andrewsi for East Timor , Forktail 20 (2004), pp. 90-91
  5. ^ Higgins, p. 929
  6. ^ Higgins, p. 930
  7. ^ Higgins, p. 930
  8. ^ Higgins, p. 931
  9. ^ Higgins, p. 931
  10. ^ Higgins, p. 931
  11. ^ Higgins, p. 931 and p. 932
  12. ^ Higgins, p. 929

Web links

Commons : White-bellied Frigate Bird ( Fregata andrewsi )  - Collection of images, videos and audio files