Black-headed Duck vs Common Eider
Heteronetta atricapilla compared with Somateria mollissima
Side-by-Side Comparison
| Attribute | Black-headed Duck | Common Eider |
|---|---|---|
| Scientific Name | Heteronetta atricapilla | Somateria mollissima |
| Order | Anseriformes | Anseriformes |
| Family | Anatidae | Anatidae |
| Conservation Status | Least Concern | Near Threatened |
| Length | — | — |
| Wingspan | 34.7 cm (13.7 in) | 56.0 cm (22.0 in) |
| Weight | 528.5 g (18.64 oz) | 2042.8333333333333 g (72.06 oz) |
| Diet | Parasitic; adults may feed on aquatic plants, seeds, and invertebrates in South American marshes. Diet … | Dives for blue mussels, clams, and crustaceans in shallow coastal waters. Swallows shellfish whole and … |
| Clutch Size | 2 | 2-7 |
| Population Trend | — | — |
Habitat Comparison
Song & Call Comparison
Black-headed Duck
Male gives a soft, raspy peeping note; female produces a muted quack. An obligate brood parasite with reduced vocalizations; subdued calls suit its secretive lifestyle among Argentine reeds.
Common Eider
Male produces a loud, resonant ah-WOOO cooing; female gives a deep, guttural quacking series. The male's iconic moaning call echoes across North Atlantic coastlines; a classic seaduck sound.
Geographic Range & Migration
Black-headed Duck
Resident in southern South America from southern Brazil and Bolivia south to Argentina and Chile. Found on lakes and marshes in open lowlands.
Common Eider
Breeds on Arctic and subarctic coasts from the North Atlantic to the Pacific. Winters along coasts of northwestern Europe and eastern North America.
Conservation Status
Black-headed Duck
Common Eider
How to Tell Them Apart
Black-headed Duck
Male has distinctive jet-black head and neck, warm chestnut-brown back, and pale buff underparts; blue-grey bill with red base. Female is streaked brown above with pale supercilium and whitish underparts.
Common Eider
Male is strikingly pied: white back, neck, and breast contrasting with black cap, belly, and flanks; nape washed pale lime-green. Female uniformly barred warm tawny-brown with darker streaks.
About These Birds
Black-headed Duck
A small diving duck (~530 g) of South America, family Anatidae, and the sole member of genus Heteronetta. Inhabits freshwater marshes and lakes in Argentina, Bolivia, Brazil, Chile, and Uruguay. Unique among waterfowl as an obligate brood parasite, laying eggs in nests of coots and other waterbirds. Feeds on seeds and aquatic invertebrates. Least Concern.
Common Eider
The heaviest duck in the Northern Hemisphere (~2 kg), family Anatidae. Breeds colonially on rocky coasts and islands of the North Atlantic and Arctic. Dives for mussels and crustaceans in shallow marine waters. Females line nests with insulating down. Near Threatened due to recent declines in parts of its range from hunting and pollution.