Crested Duck (Lophonetta specularioides) is a partially migrant, sexually monomorphic, dabbling duck that is endemic to the central Andean and Patagonian regions of South America. It comprises two subspecies: Patagonian Crested Duck (L. s. specularioides) and Andean Crested Duck (L. s. alticola; Phillips 1922–1926, Johnsgard 1978). The two subspecies inhabit different elevational environments ranging from 5000 meters in the central high Andes (L. s. alticola) to sea level in Patagonia and the Falkland (Malvinas) Islands (L. s. specularioides). The subspecies are reported to intergrade in an elevational transition zone at the latitude of Mendoza, Argentina, and Talca, Chile, respectively (Navas and Bo 1998).
Crested Duck is not likely to be confused with other South American ducks. In the field, the slim-bodied appearance, the long tail and the crested head are all distinctive. Spectacled Duck (Speculanas specularis) has prominent white facial marks aiding its recognition, even though the two species have a similar speculum (bronze-colored with a posterior black and terminal white border, lacking any anterior border differentiation) (Johnsgard 1965). Steamer-ducks (Tachyeres) are massive, blue-grayish, and they either do not fly or are very clumsy at it. Yellow-billed Pintail (Anas georgica) is smaller, uniformly brown with a slender neck and yellow bill.
The following description is based on Johnsgard (1978):
Adults: Sexes alike, males are larger than female, with a more prominent crest. Head and neck pale grayish brown, with a darker brown smudging around the eyes that fades to gray as it approaches a long but ragged crest. Feathers of mantle, back and scapulars dark brown with pale centers, giving mottled appearance. The abdomen, flanks and tail coverts are mostly light gray. The tail is distinctly elongated and black, as are the undertail coverts. The upperwing surface is gray brown to light brown, except for the secondaries, which are iridescent coppery to greenish, with a broad black band behind, and edged narrowly with white.
Juveniles: Lack crests, have light brown faces, and considerably paler abdomen than adults.
Ducklings: Brown to dark gray with white markings and long stiff tail.
No eclipse plumage. It is assumed to have two body molts and one wing molt per year (Young 2005).
Iris: yellow orange (L. s. alticola), red (L. s. specularioides)
Bill: gray, light bluish
Tarsi and toes: dark gray
L. s. alticola (n = 46) L. s. specularioides (n = 21)
Body mass (g) 1017.2 1002.1
Wing chord (mm) 294.3 261.7
Tail length (mm) 167.5 141.7
Tarsus length (mm) 61.4 61.1
Bill length (mm) 36.5 32.9
Bill height (mm) 16.5 16.1
Bill width (mm) 19.0 19.3
Skull length (mm) 108.1 101.0
Data from Bulgarella et al. (2007).