Америкалық қара үйрек туралы мәліметтер

Species of bird

The American black duck (Anas rubripes) is a large dabbling duck in the family Anatidae. It was described by William Brewster in 1902. It is the heaviest species in the genus Anas, weighing on average and measuring in length with an wingspan. It somewhat resembles the female and eclipse male mallard in coloration, but has a darker plumage. The male and female are generally similar in appearance, but the male's bill is yellow while the female's is dull green with dark marks on the It is native to eastern North America. During the breeding season, it is usually found in coastal and freshwater wetlands from Saskatchewan to the Atlantic in Canada and the Great Lakes and the Adirondacks in the United States. It is a partially migratory species, mostly wintering in the east central United States, especially in coastal areas. It interbreeds regularly and extensively with the mallard, to which it is closely related. The female lays six to fourteen oval eggs, which have smooth shells and come in varied shades of white and buff green. Hatching takes 30 days on average. Incubation usually takes 25 to 26 days, with both sexes sharing duties, although the male usually defends the territory until the female reaches the middle of her incubation period. It takes about six weeks to fledge. Once the eggs hatch, the hen leads the brood to rearing areas with abundant invertebrates and vegetation. The American black duck is considered to be a species of least concern by the International Union for Conservation of Nature (IUCN), although some populations of the species are in decline. It has long been valued as a game bird. Habitat loss due to drainage, global warming, filling of wetlands due to urbanization and rising sea levels are major reasons for the declining population of the American black duck. The United States Fish and Wildlife Service has been purchasing and managing the habitat of this species in many areas to support the migratory stopover, wintering and breeding populations. The Atlantic Coast Joint Venture also protects habitat through restoration and land acquisition projects, mostly within their wintering and breeding areas.

American ornithologist William Brewster described the American black duck as Anas obscura rubripes, for "red legged black duck", in his landmark article "An undescribed form of the black duck (Anas obscura)," in The Auk in 1902, to distinguish between the two kinds of black ducks found in New England. One of them was described as being comparatively small, with brownish legs and an olivaceous or dusky bill, and the other as being comparatively larger, with a lighter skin tone, bright red legs and a clear yellow bill. Pennant, in Arctic Zoology, Volume 2, described this duck as coming "from the province of New York" and having "a long and narrow dusky bill, tinged with blue: chin white: neck pale brown, streaked downwards with dusky lines." This species has the highest mean body mass in the genus Anas, with a sample of 376 males averaging and 176 females averaging , although its size is typically quite similar to that of the familiar mallard. The American black duck somewhat resembles the female mallard in coloration, although the black duck's plumage is darker. which is occasionally flecked with black. The head is brown, but is slightly lighter in tone than the darker brown body. The cheeks and throat are streaked brown, with a dark streak going through the crown and dark eye. Both male and female American black ducks produce similar calls to their close relative, the mallard, with the female producing a loud sequence of quacks which falls in pitch. In flight, the white lining of the underwings can be seen in contrast to the blackish underbody and upperside. The purple speculum lacks white bands at the front and rear, and rarely has a white trailing edge. A dark crescent is visible on the median underwing primary coverts. The American black duck is a habitat generalist as it is associated with tidal marshes and present throughout the year in salt marshes from the Gulf of Maine to coastal Virginia. It usually prefers freshwater and coastal wetlands throughout northeastern America, including brackish marshes, estuaries and edges of backwater ponds and rivers lined by speckled alder. with a diverse diet. It feeds by dabbling in shallow water and grazing on land. It is partially migratory, and many winter in the east central United States, especially coastal areas; some remain year round in the Great Lakes region. This duck is a rare vagrant to Great Britain and Ireland, where over the years several birds have settled in and bred with the local mallard. The resulting hybrid can present considerable identification difficulties. Both sexes share duties, although the male usually defends the territory until the female reaches the middle of her incubation period. It has been proposed that the American black duck and the mallard were formerly separated by habitat preference, with the American black duck's dark plumage giving it a selective advantage in shaded forest pools in eastern North America, and the mallard's lighter plumage giving it an advantage in the brighter, more open prairie and plains lakes. According to this view, recent deforestation in the east and tree planting on the plains has broken down this habitat separation, leading to the high levels of hybridization now observed. However, rates of past hybridization are unknown in this and most other avian hybrid zones, and it is merely presumed in the case of the American black duck that past hybridization rates were lower than those seen today. Also, many avian hybrid zones are known to be stable and longstanding despite the occurrence of extensive interbreeding. The American black duck and the local mallard are now very hard to distinguish by means of microsatellite comparisons, even if many specimens are sampled. Contrary to this study's claims, the question of whether the American haplotype is an original mallard lineage is far from resolved. Their statement, "Northern black ducks are now no more distinct from mallards than their southern conspecifics" only holds true in regard to the molecular markers tested.

The apex nest predators of the American black duck include American crows, gulls and raccoons, especially in tree nests. Habitat loss due to drainage, filling of wetlands due to urbanization, global warming and rising sea levels are major reasons for the declining population. Some conservationists consider hybridization and competition with the mallard as an additional source of concern should this decline continue. Hybridization itself is not a major problem; natural selection makes sure that the best adapted individuals have the most offspring. However, the reduced viability of female hybrids causes some broods to fail in the long run due to the death of the offspring before reproducing themselves. While this is not a problem in the plentiful mallard, it might place an additional strain on the American black duck's population. Recent research conducted for the Delta Waterfowl Foundation suggests that hybrids are a result of forced copulations and not a normal pairing choice by black hens. The United States Fish and Wildlife Service has continued to purchase and manage habitat in many areas to support the migratory stopover, wintering and breeding populations of the American black duck. In addition, the Montezuma National Wildlife Refuge has purchased and restored over 1,000 acres of wetlands to provide stopover habitat for over 10,000 American black ducks during fall migration. Also, the Atlantic Coast Joint Venture has been protecting the habitat of the American black duck through habitat restoration and land acquisition projects, mostly within their wintering and breeding areas. In 2003, a Boreal Forest Conservation Framework was adopted by conservation organizations, industries and First Nations to protect the Canadian boreal forests, including the American black duck's eastern Canadian breeding range.