Kerguelen duck
| Kerguelen duck | ||||||||||||
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Kerguelen duck |
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| Anas eatoni | ||||||||||||
| ( Sharpe , 1875) |
The Eaton's Pintail ( Anas eatoni ) is a duck bird , of the floating duck is allocated. It is a small, slim and thin-necked gudgeon duck with a predominantly dark and red-brown upper side of the body.
Within the species-rich Anatinae genus Anas , the kerguelen duck is most closely related to the South American pointed-tailed duck ( Anas georgica ) and the pintail ( Anas acuta ). The kerguelen duck, which occurs as an island in the southern Indian Ocean, has long been considered a subspecies of the pointed-tailed duck. It is now given its own species status. Apart from the introduced mallard , it is the only species of duck on the Kerguelen Archipelago , the Crozet Islands and the islands of Saint Paul and Amsterdam .
Appearance
The Kerguelen duck is smaller and slightly more compact than the pintail. It reaches a body length of 35 to 40 centimeters. The wingspan is 65 to 70 centimeters. The weight is 400 to 500 grams. The beak is noticeably slim and short.
The species shows only a slight sexual dimorphism , which normally only occurs in swimming ducks of the tropics and subtropics. The plumage is red-brown on the upper side of the body, light and cinnamon-brown on the underside of the body. About one percent of the males have a slightly more noticeable plumage. Their heads are browner and they have white stripes on their necks. Usually, the males can only be distinguished from the females by the slightly more colorful wing surface and the slightly elongated central tail feathers.
The beak is blue-gray with a black line on the ridge of the beak. The legs are dark gray. The eyes are yellow-brown. The females are slightly smaller and have a dull brown wing mirror. With them, the line on the beak ridge is a little less pronounced. Young ducks resemble the female, but are more striped on the underside of the body. Male young ducks also show a more noticeable wing mirror very early on. The chicks are very similar to those of the pintail. But they are a bit smaller and paler. The spots on the back and the wings are reddish brown and not whitish as on the pintail.
Kerguelen ducks moult their small plumage twice a year and their wings once a year. The difference between resting and splendid plumage is much less pronounced in the male Kerguelen duck than in the pintail. The plumage is just a little less spotted. The males wear the resting dress from May to November. During this time, apart from the wing mirror, they largely resemble the females.
There is only a possibility of confusion with the pointed-tailed duck, which occasionally occurs as an errant in the distribution area of the kerguelen duck.
Systematics
As early as 1824, James Francis Stephens proposed to assign the species group of pointed- tailed ducks to its own genus with the genus name Dafila . This proposal is confirmed by new morphological and molecular biological findings, but has not yet been generally accepted.
There are two subspecies of the Kerguelen duck. The nominate form A. e. eatoni occurs on the Kerguelen, the Saint Paul Islands and Amsterdam. The subspecies A. e. drygalskii is only common in the Crozet Islands. The physical characteristics of the two subspecies are difficult to distinguish. In the subspecies living on the Crozet Islands, the underside of the body is slightly less marked. The wings and beak are shorter, while the tarsi and the beak ridge are slightly longer.
distribution
The nominate form is an endemic species of the Kerguelen. The Kerguelen Archipelago is located in the southern Indian Ocean at 49 ° south latitude and 70 ° east longitude, about 4000 km from Australia, 3800 km from the South African coast and 2000 km from Antarctica. The species was introduced on the islands of Sankt Paul and Amsterdam to the northeast. The island of Amsterdam is about 10 km long, 7 km wide and has an area of 57.5 km². The highest point is the Mont de la Dives with 867 m. The coasts are very steep and inaccessible, in the west coastal cliffs up to 660 m high have formed. The St. Paul Island is of volcanic origin, is 92 kilometers south of the Amsterdam Island in the Indian Ocean and is up to 268 m high at its highest point, the Crète de la Novara. The Kerguelen duck is found here all year round in wetlands and along the coast.
The subspecies A. e. drygalskii occurs only in the Crozet Islands. These are a group of volcanic islands in the southern Indian Ocean between 46 ° and 47 ° south latitude and between 51 ° and 52 ° east longitude. They cover a land area of about 350 km². Five islands that belong to this group of islands are settled. These are the islands of Possession, East, Pig, Penguin and Apostle, all of which have vegetation.
Characteristic for large parts of the distribution area is the location in the Roaring Forties , strong winds blowing from the west all year round, which cause unstable weather, rain and high seas and often turn into storms. The climate is cold oceanic. On the Kerguelen the annual mean is 4.6 ° C (fluctuating between 23 ° C and just over 0 ° C in summer and −5 to −14 ° C in winter) and precipitation is 674 millimeters per year with a relative dryness in the Summer. The flora of the sub-Antarctic islands is extremely species-poor. There are 29 plant species on the Kerguelen.
Duration
The existence of the nominate form is probably between 45,000 and 60,000 individuals. The species will probably not be preserved on the islands of Amsterdam and Sankt Paul because it is exposed to high enemy pressure here from predators such as skuas . The stocks in the Kerguelen Archipelago are declining overall.
The existence of the subspecies A. e. drygalskii was stable between 1000 and 1350 individuals between 1966 and 1984 and was estimated at 1800 to 2100 individuals for 2002. However, the situation on the individual islands of the Crozet Islands is different. Only between one and five pairs breed on Pig Island. Here you are exposed to high pressure from feral cats. The island is apparently populated again and again by breeding pairs that come from Apostle Island.
Habitat, food and general behavioral characteristics
The Kerguelen duck mainly lives in boggy depressions, small inland lakes and in brook and river valleys. However, during the winter months they can also be observed in sheltered sea bays. The vegetation of their habitat consists of subarctic tufted grasses, low undergrowth and heather-forming dwarf shrubs. Due to the simple plumage, kerguel ducks are well camouflaged in this environment. On the Crozet Island, the kerguelen duck mainly uses the storage areas of the southern elephant seal during spring and summer .
The kerguelen duck looks for its food mainly during the day on the beaches of the ponds and bays. She also visits the elephant seals' resting areas . It mainly consumes animal food, which includes crustaceans and invertebrates, which are found in the moist bank substrate. When foraging for food, it often forms smaller groups. Larger flocks of this species of duck can often be found in the nocturnal resting places. During the moult, it probably looks for food at night as well.
The Kerguelen is very quick and agile on foot. Often it rests on rocks or larger stones. She's also a good flyer. Their small size enables them to dive like diving ducks without using their wings. During the wing moult, when the ducks are unable to fly, they usually hide on banks or under Kerguelenkohl . During this time they also use the caves to withdraw.
Reproduction
The breeding season falls from November to February. The Kerguelen duck often breeds at altitudes up to 500 meters. The nests are some distance apart and are built in grass and low vegetation. Rock bands near bodies of water are also used. The nesting trough is covered with moss and down. The eggs are pale olive green and with a size of 53.6 × 37.8 millimeters only slightly smaller than those of the pintail, although the kerguelen duck is significantly smaller than this. The full clutch has an average of five eggs. But there are also clutches with two to six eggs. The female breeds alone. The breeding season of wild kerguelen ducks is unknown.
The chicks are led by the female alone, which also entices predators . The chicks are raised in freshwater and abandoned by the female very early. The young ducks form large flocks while they are still unable to fly. Apart from the introduced cats and rats, skuas in particular are predators of the chicks. The chicks and young ducks therefore lead a very hidden life.
Human and kerguelen duck
Human impact on the population
At the height of the hunt for whales, seals and penguins on the Kerguelen between 1800 and 1870, the Kerguelen duck was hunted intensively. Since kerguelen ducks, like many other bird species found on islands, are not particularly shy of humans, the kerguelen duck is easy to hunt. The distribution area is part of the French Southern and Antarctic Lands and has no permanent residents. However, 140 researchers winter here every year and in summer the number of people present in the area can double. Since the establishment of research stations on the main island of the Kerguelen archipelago, around 200 to 300 Kerguelen ducks are shot annually between May and October. These kill numbers are said to have no effect on the number of individuals.
The introduction of cats has a potentially more problematic effect on the population of the Kerguelen duck. They were released into the wild in 1956 to control the rats and mice that had spread to the island as a result of human settlement activities. The cats have so far successfully resisted attempts to reverse this introduction. At present, petrels are still the main prey for cats. However, it is possible that the cats will focus on this species of duck when the petrels reach lower populations. Another problem is the introduced rabbits, which have permanently altered the vegetation. The kerguelen cabbage, which offers the ducks cover especially during the moulting, was pushed back by the rabbits into areas that are inaccessible to them, and on the Kerguelen it is only found scattered on a few peninsulas. In the mid-1990s, planning to restore the original Kerguelen vegetation began; Previously, the rabbits were successfully exterminated on three small islands in test runs, after which the kerguelen cabbage settled again through alluvial seeds. The ducks are currently reacting to the reduced stocks of kerguelen cabbage by staying in caves during the swing moulting during the day and looking for food at night.
Keeping in human care
The subspecies living on the Crozet Islands has not yet been imported (as of 1999). In 1951 and 1950, some individuals of the nominated form were kept in the enclosure. Breeders in the GDR who were able to breed this type of duck until 1975 were particularly successful. After that, the reproductive rate fell sharply due to inbreeding depression . The last adult from these offspring died in 1984. The breeding process at the British Wildfowl Trust was similar . The last adult bird died here in 1986. Kerguelen ducks were bred in the USA at least in 1969. Nothing is known about the adult bird population there.
supporting documents
Individual evidence
- ↑ Kolbe, p. 247.
- ↑ Kear, p. 600.
- ^ Higgins, p. 1306.
- ↑ Kear, p. 599.
- ^ Higgins, p. 1307.
- ↑ Kevin P. Johnson, Sorenson, Michael D .: Phylogeny and biogeography of dabbling ducks (genus Anas ): a comparison of molecular and morphological evidence (PDF; 1.0 MB) . In: The Auk . 116, No. 3, 1999, pp. 792-805.
- ↑ Kevin P. Johnson, McKinney, Frank; Wilson, Robert; Sorenson, Michael D .: The evolution of postcopulatory displays in dabbling ducks (Anatini): a phylogenetic perspective. ( Memento from June 29, 2006 in the Internet Archive ) . In: Animal Behavior . 59, No. 5, 2000, pp. 953-963.
- ↑ BC Livezey: A phylogenetic analysis and classification of recent dabbling ducks (Tribe Anatini) based on comparative morphology (PDF; 2.8 MB) . In: The Auk . 108, No. 3, 1991, pp. 471-507.
- ^ Higgins, p. 1307.
- ↑ Kear, p. 600.
- ↑ Kear, p. 600.
- ↑ Kolbe, p. 248.
- ^ Higgins, p. 1307
- ↑ Kear, p. 601
- ↑ Kear, p. 601.
- ↑ Kear, p. 601.
- ↑ Kear, p. 601.
- ↑ Kear, p. 601.
- ↑ Kolbe, p. 249.
- ↑ Kolbe, p. 249.
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: The world's ducks. Ulmer Verlag 1999, ISBN 3-8001-7442-1 .
Web links
- Anas eatoni inthe IUCN 2013 Red List of Endangered Species . Listed by: BirdLife International, 2012. Retrieved February 6, 2014.