American Black Duck: The Mallard Look-Alike That Is Not a Mallard

The American black duck, Anas rubripes, is the dark, mallard-shaped dabbling duck of eastern North America, and despite the name it is not black: Cornell describes “very dark brown bodies with pale gray-brown heads”. It is known for passing as a female mallard, and for a steep decline in the twentieth century in which the mallard is one of the suspects. Look for it in salt marshes, bays and sheltered ponds near the Atlantic coast, often in the same flock as mallards.

How to recognise an American black duck

Cornell puts it at “About the same size as a Mallard; slightly larger than a Gadwall”, with “a profile nearly identical to Mallards”: 54–59 cm long (21.3–23.2 in), 720–1640 g (25.4–57.9 oz), with a wingspan of 88–95 cm (34.6–37.4 in). The male has a “Dark brown body contrasting with a pale brown head and yellow bill”, with a “purple speculum, and red legs”. Females “tend to be slightly paler than males, with duller olive bills”. Cornell gives no separate eclipse plumage, and its verdict on the pair is that “The female has a darker and duller bill than the male, but is otherwise quite similar.” The bill, then, sexes the bird; more in male vs female duck. Voice will not help either: Audubon says the call “sounds like the typical duck quack”.

American black duck or female mallard?

This is the confusion that matters; Cornell says black ducks “look quite similar to female Mallards”. Cornell’s marks: “Female Mallards have paler bodies than American Black Ducks, and their bills are orange and black rather than yellow-olive.” Then the wing: “The speculum on Mallards is blue bordered with white, while the American Black Duck’s is purple without the white border.” In a mixed flock Cornell suggests looking for “a darker, colder-toned duck of similar size”, and in flight “the white underwings of American Black Ducks form a brighter, more contrasting flash than on a flying Mallard.” Hybrids blur all of this. Cornell warns of “individuals with intermediate characters, such as a dark body and a partially green head”, and a hybrid male may show “Mallard’s iridescent green on upper part of head and American Black Duck’s pale cheek.” Of the other look-alikes, mottled ducks “are slightly paler overall than American Black Ducks and have buffy, unstreaked faces”, and Ducks Unlimited notes “very limited range overlap”.

Where and when you will see one

This is an eastern bird. Ducks Unlimited says “Breeding birds occur from southern Hudson Bay east to the Maritime Provinces, and south from Maine to coastal North Carolina”. The USFWS notes that along the Atlantic coast it “frequents the salt marshes and ocean much more than mallards.” Cornell says the birds “mostly spend the winter in saltwater wetlands”. Ducks Unlimited has them leaving the breeding areas “in September or October, depending on latitude”, though “A relatively small portion of the population is nonmigratory and occupies coastal wetlands from New Jersey south to North Carolina.”

In Britain the rarity depends on whom you ask. To the BTO it is “Very rare”, “a rare vagrant”, with a first record in Kent in 1967 and an Irish one in Kilkenny in 1954; to BirdGuides’ species page it is “Scarce”. BirdGuides’ 2014 history found it “recorded in Britain and Ireland in 35 of the subsequent 47 years”, while warning that it “is no doubt rarer than the above statistic suggests”. Not all are escapes: Cornell records that “One female banded in New Brunswick, Canada, turned up later in France.”

What it eats, and how

Cornell: “These are dabbling ducks that tip up instead of dive when they forage”; the difference is set out in dabbling vs diving ducks. The species eats “mostly plant matter, with insects added during the breeding season”, when adults and ducklings take aquatic insect larvae, “crustaceans, mollusks, and sometimes fish”. Audubon, on the coast: “In tidal zones may feed mainly on mussels, clams, snails, small crustaceans, aquatic arthropods.” Inland, Cornell adds, they “fly into agricultural fields to feed on waste corn and grain.”

Nesting and ducklings

The nest is usually on the ground. Cornell: “The female selects a well-concealed site, often on the ground, on wooded or grassy islands, uplands, marshes, cultivated croplands, or cropland borders.” Cornell gives 6–14 eggs, “White, cream-colored, or pale greenish buff”, and 23–33 days of incubation; Audubon says a female “typically lays 7-11 eggs, sometimes 6-12, rarely 4-17”, incubating “typically 26-29” days, and Ducks Unlimited puts incubation at “around 26 days”. Cornell says that “As soon as their down feathers dry, newly hatched ducklings are able to leave the nest”; Audubon adds that the female leads them to water “often after dark”, and that they fly at “about 2 months”.

Do black ducks and mallards interbreed?

Yes, and the mallard has long been blamed for the black duck’s troubles. Audubon: “Clearing of forest has favored invasion by Mallards, which hybridize extensively with American Black Ducks, leading to genetic ‘swamping’ of population.” Cornell adds that “Mallards thrive under urban conditions and may oust their shyer cousins from the habitat”. A 1989 review in the Wildlife Society Bulletin noted that “Black duck x mallard hybrids are fertile” and that “Hybridization could be a result of concomitant mallard increases and black duck decreases, or changes in black duck-to-mallard ratios could be from hybridization and genetic swamping of black ducks.” Genetics has since changed the picture. Ducks Unlimited’s 2020 article on the two species reports: “We discovered a hybridization rate of 25 percent among birds identified as black ducks.” It goes on: “The remaining 75 percent were pure black ducks”, and “Mallard-black duck hybrids rarely breed with black ducks, resulting in little gene flow back into the parental black duck population.” Its conclusion turns the worry round: “Instead of the black duck being faced with genetic extinction, it is the native North American mallard that may be threatened by hybridization with game-farm birds.”

Strays pair with mallards too. BirdGuides reported in 2014 that the drake at Loch Sunart in Highland, Scotland, present “intermittently since 16th June 2007”, was “paired with a female Mallard”. Its 2019 article said “the bird has spent 12 years as a Scottish resident” and had “sired various offspring with the local Mallard population”. None of the sources we read says what became of it after 2019.

How American black ducks are doing

Better than they were, but not back. The Black Duck Joint Venture describes a bird that was “Once the most abundant fresh-water duck in eastern North America” and whose populations “have dropped steadily since the 1950s, reaching all-time lows in the 1980s”; Ducks Unlimited cites USFWS estimates that numbers “fell by more than 50 percent between the 1950s and 1980s.” Cornell records hunters “shooting an estimated 800,000 per year in the 1960s and 1970s”. The causes are argued over. The joint venture lists “Habitat loss, competition with mallards, hunting, changes in nesting and brood-rearing success”; the 1989 review found that the evidence “does not support the contention that hunting is either the sole or most important cause” of the drop in winter counts. The joint venture itself dates from 1989, in Ducks Unlimited’s words “the first species-specific joint venture established under the North American Waterfowl Management Plan”. The USFWS’s 2025 report put black ducks in its eastern survey area at 0.8 ± 0.09 million, “similar to their 2024 estimates and their long-term average”. Even so, the joint venture says, “overall numbers of black ducks are still only at about half the level of the 1950s.”

If a female mallard on a winter marsh looks too dark, check the bill, then the speculum and underwings when it flies, and confirm it with which wild duck did I see. Cornell’s oldest black duck was “26 years, 5 months old” when found in Delaware in 1978; compare that with how long ducks live.