Australian white-throated duck
| Australian white-throated duck | ||||||||||||
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Australian white-throated duck |
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| Anas gracilis | ||||||||||||
| Buller , 1869 |
The Australian white-throated duck ( Anas gracilis ), also called gray duck , is a monotypical swimming duck and the most widespread and most common duck in Australia . It belongs to the species group of white-throated ducks, which includes the Australian white-throated duck, the Sunda white-throated duck and the Andaman white-throated duck.
Appearance
The Australian white-throated duck is a small, gracefully built species of duck. With a body length between 37 and 47 centimeters, it is slightly larger than a teal duck . The wingspan is 60 to 67 centimeters. In its area of distribution, it can be confused with the chestnut duck, which, however, has significantly darker plumage than the Australian white-throated duck. Both types of duck sometimes use bodies of water which, due to the mineral content, give the plumage a reddish color. The ducks can then hardly be distinguished from one another. There are also occasional hybrids between the two species. Male ducks from such crosses then resemble male chestnut ducks when they are resting. One of the most striking characteristics of the Australian white-throated duck is the white throat spot.
Australian white-throated ducks show neither seasonal dimorphism nor pronounced sexual dimorphism . The male is slightly larger than the female. The forehead is also a little steeper in the males. However, these differences are only noticeable when couples can be observed. The safest way to differentiate between the sexes is voice and behavior. The female utters a loud croak. The males, on the other hand, have a dull pijp .
The body plumage of fully grown Australian white-throated ducks is uniformly gray and looks somewhat scaled because of the light-colored feather edges. The head has faint dotted lines and is significantly darker at the top than on the face. The chest is noticeably spotted. The upper wings are dark brown. The wing mirror is black and has a white cross-mark at the lower end. The lower wings are dark brown and white. The beak is blue-gray and darker around the edges. The legs and feet are dark gray. The eyes reddish brown. The head is often carried noticeably high. Then the relatively slim neck and the slightly elongated neck feathers are also noticeable.
Young ducks are similar to adult ducks. With them, however, the chest is more longitudinally streaked than spotted. The eyes are dark brown by the end of the juvenile moult. Young ducks renew their small plumage between the 10th and 24th week of life and between the 24th and 52nd week of life they go through their first full moult.
The small plumage of Australian white throated ducks is subject to continuous moult . The rocker and control feathers are moulted once a year after the end of the breeding season. The ducks are then unable to fly for 23 to 27 days.
The chicks are gray-brown on the top and gray-white on the underside. They are very similar to the chicks of the chestnut duck, but are a little paler overall. The chin is white. The face is brownish. A dark bridle runs through the eye. Further eye stripes below and above the eye are a little less clear. The chicks also have a dark ear mark. The beak, legs and feet are dark blue-gray.
Distribution and existence
The Australian white-throated duck is a species of duck endemic to Australia. Since it is highly nomadic, it also reaches islands in the region. For example, both the north and south islands of New Zealand are populated again and again by the wandering Australian white-throated ducks, who breed there successfully. However, New Zealand does not appear to offer sufficient suitable habitats for the Australian white-throated duck. However, the number of settlements has increased in recent years; it benefits from nesting aids in the form of artificial nesting holes. In New Zealand, the population was less than 20,000 individuals in the 1970s. The number has risen since then and is estimated at between 25,000 and 100,000 white-throated ducks for the 1990s.
Also on the Solomon Islands there were Australian white-throated ducks until the second half of the 20th century, which were sometimes even described as a subspecies of their own and then referred to as Renell's white-throated duck . The Australian white-throated duck is now extinct in the Solomon Islands after the introduction of tilapia in the only freshwater lake there, and the degradation of raw materials permanently changed the habitat.
The wandering Australian white-throated duck has also been described for the southern islands of the Moluccas , Timor and New Guinea. You can also reach the Lord Howe Archipelago , an Australian archipelago in the Tasman Sea about 630 km off the east coast of the Australian state of New South Wales. They can also be found on Macquarie Island , which is also located in the southern Pacific Ocean.
Very wide and irregular migratory movements occur above all when favorable conditions lead to very high reproduction rates. The Australian population is estimated to be at least 1.7 million Australian white-throated ducks. However, their sometimes very long migrations make it difficult to count the population. In good years the population can be 4.2 million individuals. In Arnhem Land alone , in the Alligator Rivers system , more than 50,000 non-breeding ducks gather in most years.
Habitat and diet
Australian white-throated ducks colonize almost all types of water in Australia. In addition to eutrophic lowland waters, cattle troughs, mangrove swamps and open salt lagoons are also accepted. However, breeding populations predominantly occur in the southeast and east of the Australian continent. Most of these are freshwater inland. A small part of the population also breeds in the coastal areas, where the chestnut duck is the most common.
The ingestion of food takes place primarily in the process of being and being and only occasionally diving. With regard to the composition of the food, individual studies have come to different results. It is generally believed that the majority of the diet consists of invertebrates. However, gastric analyzes have also revealed large parts of the vegetable diet.
Reproduction
The white-throated duck mainly builds their nests in tree hollows. The trees used as nesting sites are either in flowing waters, inland waterways or in floodplain areas. In most of their Australian habitat, the breeding season is from June to February. Clutches also occur in other months when rains and floods have created suitable conditions. In New Zealand, the peak of the breeding season is between September and November.
A nest building in the narrower sense does not take place. However, the nest box is equipped with pale gray down. The choice of nesting site is part of the courtship repertoire.
The eggs are elliptical. The skin is smooth and cream-colored. The laying interval is one day. The full clutch comprises between four and 17 eggs. However, an average clutch contains 8.9 eggs. Clutches with up to 32 eggs have already been found. In this case, however, several females have laid eggs in one nest.
The female breeds alone. The breeding season averages 28 days. The male stays near the brood cavity and accompanies the female during her breeding breaks. The breeding breaks usually take place in the early morning, at noon and one last time in the late afternoon. Overall, the female only leaves the eggs for about an hour a day. The male defends the nesting place especially during the egg-laying and during the first weeks of the breeding season. This behavior clearly subsides in the third week. Both parent birds lead the young birds, but they are only fledged by the female . If the female dies shortly after the chicks hatch, the male is able to raise the brood on his own. Occasionally they still form a family group with their parent birds when they are already fledged. Sexual maturity is reached after a year. In the case of Australian white-throated ducks in the Canberra region, in which reproductive success was measured, 221 downy chicks hatched from 235 eggs. Only 83 of the chicks fledged. The death rate was highest during the first two weeks of life. In addition to predators, unfavorable weather conditions and insufficient food contribute to the high mortality rate.
Australian white-throated ducks often raise more than one clutch per breeding season. The second clutch is usually laid when the young ducks from the first brood fledge. In exceptional cases, however, the time interval between the individual scrims can also be significantly shorter. The earliest observed laying of the second clutch occurred 32 days after the chicks of the first clutch had hatched. Replacement clutch after a clutch has been lost or even the chicks are sometimes already laid after three weeks.
Keeping in human care
Australian white-throated ducks do not play a major role in the keeping because of their inconspicuous plumage. The species was first imported in 1882 and then kept at the London Zoo. In 1960 the British Wildfowl Trust acquired ducks of this type for the first time. The keeping is considered to be problem-free. The reproduction rates are high.
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
- ↑ a b Kear, p. 570
- ↑ Higgins, p. 1266
- ^ Kear, p. 569
- ↑ a b c d Kolbe, p. 233
- ↑ Higgins, p. 1267 and p. 1268
- ↑ a b c d e f Kear, p. 571
- ^ Kolbe, p. 234
- ^ Higgins, p. 1274
- ^ Kear, p. 572
- ↑ Higgins, pp. 1277-1278
- ^ Kear, pp. 571 and 572
- ↑ Kolbe, p. 235
Web links
- Anas gracilis inthe IUCN 2013 Red List of Threatened Species . Listed by: BirdLife International, 2012. Retrieved October 12, 2013.