Adult Plumage:
Summer Plumage:
- Forehead, crown, and a band on the upper neck are dark brown.
- The area around the eyes and chin are darker in coloration.
- The back is dark brown, but slightly lighter than the crown.
- Primary flight feathers are light brown, with the base and hidden portions of the vanes being a lighter hue.
- Secondary flight feathers are brown, becoming progressively whiter towards the inner feathers.
- The sides of the head, neck, and chest are rufous, but slightly darker on the sides of the head and lighter on the front of the neck.
- The belly is silvery-white. The sides of the flanks and the posterior belly display brown spots or are entirely brown.
Winter Plumage:
- The crown and neck are the same color as the back.
- Chin is white.
- The belly transitions to rufous.
Juvenile Plumage:
- Has a paler plumage overall.
- Lacks rufous coloring, or has only a small streak on the sides of the head.
- The underside is white, with a slight brownish tinge.
Physical Characteristics:
- Eyes: Reddish-brown.
- Beak: Black. The tip of the beak is light horn-brown; the edges of the beak can vary from yellow to green, often being yellowish-green.
- Legs and Toes: Black, slightly bluish, or nearly completely black.
Measurements:
- Wing: 94 – 110 mm
- Tarsus: 30 – 35 mm
- Beak: 18 – 24 mm
Distribution:
The species is distributed in eastern China (including Hainan and Taiwan), northern Thailand, Vietnam, Laos, Cambodia, Malaysia, Sumatra, Borneo, and the Philippines.
In Vietnam, it is common in the plains. It is less frequently encountered in the midlands and mountainous regions. Many specimens have been collected in Phú Thọ, Hòa Bình, Sơn La, Lai Châu, Bắc Cạn, Lạng Sơn, and small ponds in the Trường Sơn (Central Central region).