The American black duck somewhat resembles the female mallard in coloration, although the black duck's plumage is darker. Males and females 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, 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. The speculum feathers are iridescent violet-blue with predominantly black margins. The fleshy orange feet of the duck have dark webbing. 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. Juveniles resemble adult females but have broken narrow pale edges of underpart feathers, which give a slightly streaked rather than scalloped appearance, and the overall appearance is browner rather than uniformly blackish. Juvenile males have brownish-orange feet while juvenile females have brownish feet and a dusky greyish-green bill.
American black ducks are found in eastern North America. In Canada, their range extends from northeastern Saskatchewan to Newfoundland and Labrador. In the United States, they are found in northern Illinois, Michigan, New Jersey, Ohio, Connecticut, Vermont, South Dakota, central West Virginia, Maine, and on the Atlantic coast to North Carolina. These birds are partially migratory species, mostly wintering in the east-central United States, especially in coastal areas. They live in tidal marshes and usually prefer freshwater and coastal wetlands, including brackish marshes, estuaries, and edges of backwater ponds and rivers lined by speckled alder. They also inhabit beaver ponds, shallow lakes with sedges and reeds, bogs in open boreal and mixed hardwood forests, as well as forested swamps. During winter, American black ducks mostly inhabit brackish marshes bordering bays, agricultural marshes, flooded timber, agricultural fields, estuaries, and riverine areas.
American black ducks are gregarious and may gather in flocks that number thousands of birds. They are excellent swimmers and often dive in order to avoid predators. American black ducks are active during the day spending most of the time foraging alone or in small groups. They feed by dabbling (submerging their heads, or "tipping up") in shallow water and grazing on land. American black ducks communicate with each other vocally. Females usually produce a loud sequence of quacks that falls in pitch and males make a 'kwek-kwek' sound. These are partially migratory birds, and many winter in the east-central United States, especially coastal areas; some remain year-round in the Great Lakes region.
American black ducks are omnivorous birds. Their plant diet primarily includes a wide variety of wetland grasses and sedges, and the seeds, stems, leaves, and root stalks of aquatic plants, such as eelgrass, pondweed, and smartweed. Their animal diet includes mollusks, snails, amphipods, insects, mussels, and small fishes. Ducklings mostly eat water invertebrates for the first 12 days after hatching, including aquatic sowbugs, snails, mayflies, dragonflies, beetles, flies, caddisflies, and larvae. After this, they shift to seeds and other plant food.
American black ducks are monogamous and mated pairs may stay together for years. Pair bonds are usually formed in the fall and winter before migrating to breeding grounds. They breed in habitats that include alkaline marshes, acid bogs, lakes, ponds, rivers, marshes, brackish marshes, and the margins of estuaries and other aquatic environments. In the southern part of their range, the nesting period starts in February while in the northern part, it starts in late May. Nest sites are well-concealed on the ground, often in uplands. Females lay 6 to 14 oval eggs, which have smooth shells and come in varied shades of white and buff green. The incubation period varies but usually takes 25 to 26 days. Both parents share duties, although the male usually defends the territory until the female reaches the middle of her incubation period. The ducklings hatch fully developed (precocial), and once they are dry the mother leads her brood to rearing areas with abundant invertebrates and vegetation. Ducklings fledge 6 weeks after birth and become independent from their mother.
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 American black ducks. They have long been valued as game birds, being extremely wary and fast-flying. American black ducks are also sensitive to pollution. Ducklings often catch diseases transmitted by bites of insects such as blackflies. They are also vulnerable to lead shot poisoning, known as plumbism, due to their bottom-foraging food habits.
According to the University of Michigan (Museum of Zoology) resource, the total population size of the American black duck is around 50,000 individuals. According to the What Bird resource, the total population size of the species is around 400,000 individuals. Overall, currently, American black ducks are classified as Least Concern (LC) on the IUCN Red List, but their numbers today are decreasing.
