Adult Male:
Summer Plumage: Generally, the plumage is brown-gray with numerous streaks. The forehead is white. The head, nape, elongated nape feathers, and the rear of the upper neck exhibit an iridescent purplish-red or green sheen, depending on the viewing angle. The chin and throat are white, extending to the rear of the neck to form an almost complete white band on the upper neck. Following this is a slightly wider, iridescent green band, succeeded by another white band. The lower neck, chest, upper back, shoulders, and flanks are dark brown with white streaks. The black and white streaks on the foreneck and chest are broader and more distinct, while the streaks on the longest axillary feathers are very small. A small black patch is present on the outer shoulder. The back and rump are brown. The uppertail coverts are gray with black tips, while the longest feathers are entirely black. The tail feathers are gray with white edges. The wing coverts are gray, with the greater wing coverts having pale white edges. The primary and secondary flight feathers are dark gray. The speculum (wing patch) is iridescent green with white edges. The tertials are very long, narrow, and curved into a sickle shape. They have white shafts, dark gray outer webs with narrow white edges, and inner webs with gray edges. The belly is white with brown-gray streaks similar to the flanks, but paler. The undertail coverts are black with two yellow patches and black feather bases on each side.
Winter Plumage: Resembles the female plumage, but is grayer, and sometimes lacks the sickle-shaped tertials.
Female:
The head and back are dark brown with pale rufous edges. The speculum is similar to that of the male, but less iridescent green. The belly is light gray with indistinct brown streaks.
Juvenile:
Similar to the female, but the back is darker. Lacks sickle-shaped tertials.
Other characteristics:
Eyes: Dark brown.
Bill: Black.
Legs: Brown or yellowish tinged with green; toes and webbed feet are black.
Measurements:
Wing Length: (Male): 230 – 257 mm, (Female): —
Tail Length: 77 – 84 mm;
Tarsus: 35 – 40 mm;
Bill Length: (Male): 43 – 47 mm, (Female): 40 – 43 mm.
Weight: 0.64 – 0.75 kg.
Distribution:
The Falcated Duck breeds in southeastern Soviet Union, northeastern China, North Korea, Mongolia, and Japan. They migrate south for the winter.
In Vietnam, the Falcated Duck is rare, and is usually observed in small flocks in the Northern delta region and in Hue, mixed with flocks of Gadwall or other ducks.