Sea Ducks

There are 4 species of eiders:

• Steller’s Eider (Polysticta stelleri)
• Spectacled Eider (Somateria fischeri)
• King Eider (S. spectabilis)
• Common Eider (S. mollissima)

Common Eider (female front, males back) in Sweden ©Con Foley

The Harlequin Duck (Histrionicus histrionicus) is a distinctive duck of north North America and Eurasia.

Harlequin Duck in Yellowstone National Park, US ©Tan KH

There are 5 species of scoters:

• Surf Scoter (Melanitta perspicillata)
• Velvet Scoter (M. fusca)
• White-winged Scoter (M. deglandi)
• Common Scoter (M. nigra)
• Black Scoter (M. americana)

Black Scoter (left male, right female) in Japan ©Con Foley

The Long-tailed Duck (Clangula hyemalis) breeds in northern North America and Eurasia, but during winter, it can reach as far south as Thailand on rare occasions. The male has a distinctive black-and-white plumage, while the female has a dark cap and brown breast and wing coverts.

Male Long-tailed Duck in Japan ©Con Foley

Female Long-tailed Duck in Japan ©Con Foley

Non-breeding Long-tailed Duck in Thailand ©Con Foley

There are 3 species in the genus Bucephala, but only the two goldeneyes, Common Goldeneye (B. clangula) and Barrow’s Goldeneye (B. islandica), could be confused with each other. The male could be distinguished by the rounder white face patch and more white on wing for the former; the female could be distinguished by much less yellow on the bill for the former.  The Bufflehead (B. albeola) has a distinctive big white patch on the head (bigger in male).

Male Common Goldeneye in ID, US ©Tan KH

Female Common Goldeneye in Yellowstone National Park, US ©Tan KH

Male Bufflehead in ID, US ©Tan KH

Female Buffleheads in ID, US ©Tan KH

The Smew (Mergellus albellus) is a distinctive black-and-white duck of Eurasia.

There are 5 species of mergansers:

• Hooded Merganser (Lophodytes cucullatus) of North America – distinctive big white patch on head in male.
• Brazilian Merganser (L. octosetaceus) of South America – distinctive green iridescent head in both sexes and overall dark greyish plumage.
• Common Merganser (L. merganser) of North America and Eurasia – the male has an iridescent dark green head and upper neck, white body with black back; the female has a brown head with white chin, and greyish body.
• Red-breasted Merganser (L. serrator) of North America and Eurasia – the male has an iridescent dark green head, white body with brown breast, grey flanks and black back; the female has a brown head, greyish body with white belly.
• Scaly-sided Merganser (L. squamatus) of eastern Asia – the male has a black head, white body with black back and scaly flanks; the female has  brown head, greyish body with scaly flanks and white belly.

Hooded Merganser (male left, female right) in ID, US ©Tn KH

Common Merganser (male right, female left) in ID, US ©Tan KH

Male Red-breasted Merganser in Japan ©Con Foley

Female Red-breasted Merganser in Japan ©Con Foley

Reference
http://www.worldbirdnames.org/ioc-lists/master-list-2/