Orinocogans
| Orinocogans | ||||||||||||
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Orinocogans ( Neochen jubata ) |
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| Systematics | ||||||||||||
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| Scientific name of the genus | ||||||||||||
| Neochen | ||||||||||||
| Oberholser , 1918 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Neochen jubata | ||||||||||||
| ( Spix , 1825) |
The Orinoco Goose ( Neochen jubata ) is a South American bird art from the subfamily of tadorninae that the family of ducks counts. The characteristics of the half-geese include their goose-like habit and pronounced long legs. This feature is particularly noticeable in the Orinocogans.
The species was first described as Anser jubata in 1825 by the German scientist Johann Baptist von Spix . The genus description Neochen , the only representative of which is the Orinocogans, was made in 1918 by the American ornithologist Harry Church Oberholser .
Appearance
The Orinoco goose is a large duck bird with a goose-like appearance. It is characterized by the upright posture that the birds show even when they are propped up on large branches. In its natural range, the Orinocogans is unmistakable because there is no other bird species of this size and habit.
The Orinocogans are between 61 and 66 centimeters tall. The gander weighs around 1800 grams. Females are significantly lighter and weigh an average of 1327 grams. The head, neck and front chest are cream or beige in color. The front part of the trunk is colored rusty brown, with the color of the neck continuing on the feathers and forming a transition in the chest area. On the back and on the upper edges of the flanks, the light tone of the neck area prevails again. The rust-brown color extends up to half of the leg fletching, underneath there is another stripe in beige. The shoulder plumage and the inner arm-covers are glossy green-black, the hand wings are dark brown to black, as well as the lower part of the trunk behind the legs and the control feathers. The under tail-coverts are white, as are the inner arm wings. The long strong legs are dark pink. The resting and the splendid dress does not differ in this species. It also does not show any pronounced gender dimorphism . Females are only slightly smaller and their neck feathers are less long than the male. Not yet sexually mature young birds resemble the adult birds in their appearance. However, their body coloring is less pronounced and the beak and legs are less colorful.
The moulting scheme has not yet been adequately described for this species. It is so far unclear whether this half-geese moults its small plumage once or twice a year. Flightless Orinoco geese are observed in Venezuela in the period from March to May due to the wingtip moult . In the Orinoco geese with chicks, however, no rocking moult has been observed so far. The ornithologist Hartmut Kolbe, who specializes in ducks, suspects that adult birds do not fully moult until after they have brooded. The small plumage moult, on the other hand, before the brood.
Downy chicks have a basic white color. The headstock, the rear edge of the neck, the wings, the middle back as well as a small eye stripe, a spot in the ear area and a spot on the thigh are all black-brown. The beak is gray and the feet are pale flesh-colored.
Distribution area and existence
The distribution area of the Orinocogans extends east of the Andes from Colombia , Venezuela and Guyana south to Peru , Bolivia , Paraguay , Brazil and in the east of Ecuador . The main distribution area of the Orinocogans is the Amazon and its tributaries, as well as the Orinoco . The Orinocogans has also been observed as a stray visitor in Barbados . Orinoco geese are resident birds .
The population of this species was estimated by Wetland International in 2002 at 25,000 to 100,000 individuals. The organization assumes that the population numbers are declining.
The IUCN classifies this species as near threatened . But this does not apply to all areas of their distribution area. In Peru, this species is considered to have largely disappeared. It is also absent in previous areas of distribution in Colombia. In Bolivia, Venezuela and Argentina, however, the population is considered stable. The species is even common in some of these regions. The causes of the population decline include hunting pressure and the destruction of the tropical rainforest . As a cave breeder, this species is dependent on older tree populations that have sufficiently suitable tree hollows.
Habitat and way of life
The habitat of the Orinocogans are wooded river banks of the lowlands and tree-lined islands. It also occurs in marshland when they have a certain tree population. Among all demi-geese, it shows the most tree-related way of life and can usually be observed erect. Like the Radjahgans of the same subfamily common in tropical New Guinea and Northern Australia, it swims very rarely. Mostly couples or small family groups can be observed. It feeds mainly on plants and seeds as well as berries . To a small extent, it also takes in the larvae of invertebrates, as well as worms and small shellfish.
Reproduction
The reproduction of the Orinocogans in the wild has not yet been adequately studied. The main findings come from animals kept in zoos.
Males show pronounced aggressive behavior during the breeding season. Males penetrating the breeding area are driven away by the owner of the area with beak bites and flapping their wings. In northern South America, the eggs are laid between December and January. The nest is mostly in tree hollows or in burrows on steep river banks. Brood directly on the ground does occur but is rare. The clutch contains six to 10 pale, brown eggs. The female breeds alone. The information about the incubation period is different. According to some authors, the Orinoco geese incubate for 28 to 30 days, according to other studies, however, 32 to 34 days. The breeding success is generally not very high. In a study of the breeding success in tree hollows compared to artificial nest boxes, only 8.3 percent of the eggs in tree hollows hatched downy chicks. In contrast, when nesting in nesting boxes, a downy chick hatched from every fifth egg. Compared to other ducks, this is a below-average hatching rate. However, the juvenile mortality rate appears to be lower than is otherwise characteristic of ducks.
So far, there is insufficient data on the age at which Orinoco geese become sexually mature or what the mortality rate is in adult Orinoco geese.
Attitude in Europe
Orinoco geese were first acquired by the London Zoo in 1830. World first breeding took place in Great Britain in 1844. The British Wildfowl Trust started a breeding program for this species from 1952 onwards. However, this species remained a species rarely shown in zoos until the 1980s. Since Orinoco geese are cold-sensitive and stress-prone animals was (and still is) their demeanor as demanding. Brooding Orinoco Geese are aggressive and must be kept in individual enclosures. Since the laying period begins in February and March, the Orinoco geese are usually kept in temperature-controlled shelters.
supporting documents
Individual evidence
- ↑ a b Kear, p. 408
- ↑ Kolbe, p. 149
- ^ Neochen jubata in the IUCN Red List of Threatened Species 2011.2. Listed by: BirdLife International, 2011. Retrieved November 13, 2011.
- ↑ a b c Kear, p. 409
- ↑ Kolbe, p. 150
literature
- Janet Kear (Ed.): Ducks, Geese and Swans. Oxford University Press, 2005, ISBN 0-19-854645-9 .
- Hartmut Kolbe; Die Entenvögel der Welt , Ulmer Verlag 1999, ISBN 3-8001-7442-1
