Adult Male:
- Summer Plumage: Overall, the plumage is mahogany brown. The head and the upper three-quarters of the neck are chestnut brown. The chin is white. The lower neck is the same color but darker, forming a distinct collar around the base of the neck. The back, shoulders, rump, and wings are blackish-brown, slightly iridescent, particularly the innermost primary feathers. The base of these primary feathers is white. The wing speculum is white with a black border on the posterior side. The breast, chest, and flanks are mahogany brown, slightly darker than the head, and clearly distinct from the belly. The lower belly is blackish-brown with white speckling.
- Winter Plumage: Similar to summer plumage, but the colors are slightly duller.
Female:
- Generally resembles the male, but chestnut brown is replaced by mahogany brown. The crop, forebreast, and flanks are pale chestnut, with no clear boundary with the belly.
Juvenile:
- Similar to the female plumage but paler. Eyes are white, occasionally with a slightly yellowish or pale brown tint. The eyes of the female are usually gray or grayish-brown; older individuals have white eyes. The beak is dark gray or bluish. The legs are lead-gray with blackish-gray webs.
Measurements:
- Wing (male): 177 – 193 mm, (female): 170 – 185 mm
- Tail: 81 – 86 mm
- Leg: 29 – 32 mm
- Beak: 27 – 30 mm
- Weight (male): 0.50 – 0.65 kg, (female): 0.41 – 0.60 kg
Distribution:
This duck species is distributed from the Mediterranean to Tibet. In winter, it migrates to North Africa, India, Myanmar, Thailand, and Indochina.
In Vietnam, this species occurs in winter in the northern delta region, Hai Duong, and Phu Tho provinces, but the numbers are not large.