Adult Appearance:
Summer Plumage:
The plumage of the adult bird in summer exhibits the following characteristics: The upper head, from the rear of the forehead to the nape, is a velvety black. The forehead is white, sometimes extending to the eyes. The back is pale gray, transitioning to white or very pale gray on the flanks and upper tail coverts. The tail is white. The outer two or three primary feathers are gray with white shafts and a broad white band on the inner margin; the other primary feathers and secondary feathers are gray, edged with white on the inner side. The underparts are white.
Winter Plumage:
In winter, the plumage shows the following variations: the crown is tinged with white, and the upper tail coverts are a darker gray. The eyes are dark brown. The beak is orange-yellow with a black tip. The legs are orange-yellow.
Measurements:
- Wing: 162 – 189 mm
- Tail: 75 – 95 mm
- Tarsus: 20 mm
- Bill: 26 – 32 mm
Distribution:
This species is distributed along the coasts of West Lan, Burma, Thailand, Indochina, Malaysia, and China.
In Vietnam, this species occurs along the coast and river mouths of the central Central region.