Radjahgans
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Radjahgans |
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| ( Lesson , 1828) |
The Radjahgans ( Tadorna radjah ) is a species of the duck bird family and is one of the so-called half geese, which occupy a systematic position between the geese and the actual ducks . The Radjahgans is predominantly white with a showy flesh-colored beak and equally colored legs. Its appearance is so characteristic that it cannot be confused with any other species. Their distribution area is the north of Australia, New Guinea and the Moluccas. Two subspecies are described, which differ slightly in their body color.
The Radjahgans is the only species among the Kasarkas that is native to the tropical climate. The Australian Kasarka , which belongs to the same genus and , like the Radjahgans, is an endemic species of the fauna of Australia , occurs only in the temperate climatic zone in southern Australia. The IUCN classifies the cycle goose as not endangered ( least concern ).
The name Radjah seems to indicate a bird native to India. However, the term Radjah comes from a language native to the Moluccas and means bird.
Appearance
The Radjahgans is a small species within the genus of the Kasarkas and reaches a body length between 48.5 and 61 centimeters. The wing span is 90 to 99 centimeters. The males weigh an average of 930 grams, while the females weigh 840 grams. The sexual dimorphism is not very pronounced in this species. However, females usually have a narrower breast band and the two sexes differ in their call repertoire. Males call loud and deep Karrr , the females on the other hand a low and high Kirrr, Kirrr, Kirrr . The species can usually be observed in pairs. They prefer to sit on stones or horizontally lying tree trunks at the edge of the water.
Their body plumage is predominantly white, the back plumage is dark in the nominate form and a narrow black band runs across the chest. The subspecies Tadorna radjah rufitergum , on the other hand, is red-brown on the back and the chest markings . The beak and legs of both subspecies are flesh-colored pink. The eyes are white.
Cycling geese do not have a splendid and serene dress that changes in color distribution. The moulting scheme of this species has not yet been adequately researched.
The headstock of newly hatched Radjah geese is chestnut brown. It is bordered by a broad black-brown eye stripe that extends from the base of the beak to the rear edge of the neck. The back is dark brown. The abdomen and the spots on the sides of the body are white. The beak and the feet of the downy chicks are already flesh-colored pink, like those of the adult birds. Young birds are colored like the adult birds, but overall a little duller in color. In particular on the head there are also isolated gray and brown feathers. The edges of the flanks and the under tail-coverts are usually washed out gray-brown. Their irises are also brown.
Distribution area and existence
The nominate form is common in the coastal area of New Guinea and the Moluccas. The subspecies rufitergum has a disjoint distribution area in the tropical north of Australia. It occurs in the extreme northeast of the Australian state of Western Australia , in the Northern Territory and in Queensland . The migratory movements within this distribution area have so far been insufficiently investigated. Presumably there are local migrations between the breeding areas and wetlands, which have sufficient living space even during the dry season.
The range of the Radjahgans in Australia has decreased in the course of the 20th century. Locally, populations decline when wetlands are converted into agricultural land or cut up by roads. The increased rice cultivation in the Australian Northern Territory is particularly threatening. The population in Australia was around 150,000 individuals at the beginning of the 21st century. There is insufficient data on the population in New Guinea and the Moluccas. The population for these islands is estimated to be between 10,000 and 100,000 birds.
Habitat and way of life
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The Radjahgans lives in regions that are characterized by monsoon rains. It occurs in marshland and swamp areas as well as estuaries and also in waters with salt or brackish water. She shows a strong preference for shallow waters. During the dry season, it is mainly found on rivers and marshland surrounded by mangroves. They are typical forest dwellers who spend a large part of their resting time sitting on large branches. Open water areas are rarely visited.
Cycling geese look for their food mainly in the early morning and late evening. They also go looking for food at night. Their diet has not yet been conclusively investigated. It is believed that shellfish and other aquatic invertebrates predominate. But it also eats seeds. Feeding grounds are muddy banks and shallow water zones as well as adjacent meadows. During the day she rests erect at the edge of the water. Their resting places and their feeding grounds are occasionally up to six kilometers apart. It alternates between resting places and feeding grounds with a very flat flight. Usually it follows the water and flies close to the water surface. In wooded regions, it flies through the trees rather than over these wooded areas. What is also noticeable about this species is that they rarely swim in the water. Cycling geese are good runners, however.
Usually they are observed in small groups of six to eight individuals or in pairs. During the dry season, however, they increasingly move to larger bodies of water and then form schools of 20 to sixty individuals. Occasionally, swarms with more than 200 individuals are also counted. During the breeding season they are territoria. Each individual or pair also has their own feeding ground. There is no noticeable defensive behavior in this area, but other wheeled geese avoid this area.
Reproduction
Little is known about the mode of reproduction of the Radjahgans. The beginning of the breeding season coincides with the beginning of the rainy season. With the beginning of the rainy season, a couple occupies a breeding area. The nesting site is also within this breeding area. On Adelaide , a couple defends an average of three kilometers of shore. Unlike the feeding grounds, these breeding grounds are vigorously defended. The antagonistic behavior towards conspecifics is probably also part of the pair bond behavior.
The egg-laying takes place as soon as the water levels drop again, revealing floodplains that serve as feeding grounds for the Radjahgans. In the Northern Territory, the egg-laying time falls between February and May. In Queensland, on the other hand, from November to January. The shift in the breeding season between these regions is due to the fact that the rainy season begins at different times and lasts differently in both regions. As is typical for other types of Kasarkas, the Radjahgans is a cave breeder. It mainly uses tree hollows. Both pairs vigorously defend their breeding ground. The average clutch size has not yet been adequately investigated; clutch sizes of 6 to 15 eggs are mentioned in the literature. However, large clutches can be due to two females laying eggs in a nest. The female breeds alone. However, the male stays close to the nest and is also involved in raising the downy young.
Attitude in Europe
The first cycle geese were kept in France in 1886. Further imports to Europe took place in 1900 and 1904. The first breeding succeeded only in 1940 in a British zoo and in 1962 also a US zoo succeeded in breeding. To this day, the Radjahgans is considered to be the most difficult species to breed among the Kasarkas . In Central Europe it must also be housed in temperature-controlled shelters. Accordingly, it is rarely shown in zoos.
Allocating the wheeled geese shown in European zoos to subspecies is problematic: the animals in the enclosure are predominantly in the nominate form. In the course of time, however, the red-backed subspecies rufitergum was crossed.
supporting documents
literature
- PJ Higgins (Ed.): Handbook of Australian, New Zealand & Antarctic Birds , Volume 1, Ratites to Ducks, Oxford University Press, Oxford 1990, ISBN 0195530683
- Janet Kear (Ed.): Ducks, Geese and Swans. Oxford University Press, 2005, ISBN 0198546459 .
- Hartmut Kolbe; Die Entenvögel der Welt , Ulmer Verlag 1999, ISBN 3-8001-7442-1
Individual evidence
- ↑ BirdLife Factsheet on the Radjahgans , accessed April 9, 2011
- ^ Higgins, p. 1218
- ↑ Kolbe, p. 144
- ^ Kear, p. 423
- ↑ Kolbe, p. 144
- ↑ Higgins, p. 1219
- ↑ Higgins, p. 1219
- ↑ Kear, p. 424
- ↑ Higgins, p. 1219
- ↑ Kear, p. 424
- ↑ Higgins, p. 1219
- ↑ Higgins, p. 1220
- ↑ Higgins, p. 1220
- ^ Kear, p. 425
- ↑ Higgins, p. 1221
- ↑ Kolbe, p. 145
Web link
- Tadorna tadornoides inthe IUCN Red List of Threatened Species 2013.1. Listed by: BirdLife International, 2012. Retrieved October 13, 2013.