Duck

The ducks you’ve actually seen

Most ducks in city ponds, public parks, and roadside wetlands across temperate North America, Europe, and Asia are mallards. They’re so widespread, so adaptable, and so tolerant of human company that they’ve effectively become the default duck. The familiar “duck quack” sound — and almost every cartoon duck — derives from the mallard.

Sexual dimorphism

Mallards are textbook examples of sexual dimorphism in birds:

• Drakes (males) in breeding plumage have an iridescent green head, a white neck ring, a chestnut breast, gray flanks, and a curled black tail.
• Hens (females) are mottled brown — nearly perfect camouflage for sitting on a nest.
• Drakes in eclipse plumage (after breeding) molt to female-like brown for several weeks before re-developing breeding colors.

The iridescent green of a male mallard’s head isn’t pigment — it’s a structural color, the same physics that produces the colors of peacock trains and hummingbird gorgets. Viewed at certain angles, the head can look black or violet.

A 4,000-year domestication

Almost all domestic duck breeds are descended from mallards. Domestication began in China around 2,500 BC, and selective breeding has produced dozens of varieties — Pekin (the white meat-duck), Khaki Campbell (egg layers), Indian Runner (upright posture), Muscovy (a separate species, Cairina moschata, used for meat).

Backyard mallards near urban parks often interbreed with domestic ducks that have escaped or been released, producing the mottled “pseudo-mallards” of varied size and plumage seen at city ponds.

Hybridization risk to other species

The mallard’s adaptability is good for the species but bad for some of its relatives. Mallards readily hybridize with several closely related ducks — including the American black duck, the Mexican duck, and the Hawaiian duck (koloa). In each case, the mallard genes flood into the smaller relative’s gene pool through repeated crosses, and the rarer species is genetically swamped.

The Hawaiian duck is particularly threatened. Conservation efforts now include controlling feral mallard populations on Hawaiian islands.

The hen knows the way

Mallards have a remarkable form of imprinting: ducklings learn migration routes and breeding-pond locations from their mother. A duckling raised by a non-migrating domestic mother will likely never migrate, even though wild mallards from the same region do. Conversely, captive-raised wild mallards released without a guide flock often fail to migrate properly — they head in random directions.

This makes the mallard’s migratory behavior partly culturally transmitted, not purely genetic.

Drakes and hens in winter

Outside breeding season, mallards form huge mixed-sex flocks. Pair bonds are usually established in fall and winter, before the spring breeding migration. By the time a pair reaches the breeding grounds, they’ve been together for months.

The mating itself is fast and often forceful — a feature of duck biology that’s the subject of ongoing scientific interest. Female mallards have evolved unusual reproductive anatomy in response.

A continental dialect

Recent research using bioacoustic analysis has shown that female mallards have regional dialects in their quacking — subtly different patterns in different parts of Europe and North America. The differences are similar to the sub-species variations heard in songbird songs, suggesting cultural transmission of vocal patterns even in waterfowl.