page_title: American black duck
section_title: Breeding
hierarchical_section_title: American black duck / Behavior / Breeding
caption_attribution_description: English: An American Black Duck (Anas rubripes top left) and a male Mallard (Anas platyrhynchos bottom right in eclipse plumage). Français&#160;: Un canard noir (Anas rubripes en haut à gauche) et un canard colvert (Anas platyrhynchos en bas à droite en plumage éclipse).
context_page_description: The American black duck 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 720–1,640 g on average and measuring 54–59 cm in length with a 88–95 cm wingspan. It somewhat resembles the female 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 upper mandible. 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.
context_section_description: The breeding habitat includes alkaline marshes, acid bogs, lakes, ponds, rivers, marshes, brackish marshes and the margins of estuaries and other aquatic environments in northern Saskatchewan, Manitoba, across Ontario, Quebec as well as the Atlantic Canadian Provinces, Great Lakes and the Adirondacks in the United States. 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.
  Nest sites are well-concealed on the ground, often in uplands. Egg clutches have six to fourteen oval eggs, which have smooth shells and come in varied shades of white and buff green. On average, they measure 59.4 mm (2.34 in) long, 43.2 mm (1.70 in) wide and weigh 56.6 g (0.125 lb). Hatching takes 30 days on average. The incubation period varies, but usually takes 25 to 26 days. Both sexes share 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 interbreeds regularly and extensively with the mallard, to which it is closely related. Some authorities even consider the black duck to be a subspecies of the mallard instead of a separate species. Mank et al. argue that this is in error as the extent of hybridization alone is not a valid means to delimitate Anas species.
  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. As birds indistinguishable according to the set of microsatellite markers still can look different, there are other genetic differences that were simply not tested in the study.
  In captivity studies, it has been discovered that most of the hybrids do not follow Haldane's Rule, but sometimes hybrid females die before they reach sexual maturity, thereby supporting the case for the American black duck being a distinct species.
caption: A female American black duck (top left) and a male mallard (bottom right) in eclipse plumage
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