Adult Description:
The head and neck are black, transitioning to a darker gray on the dorsal side and a lead-gray on the belly. The breast and mid-belly are lighter in color, and the area beneath the tail is darker. The primary and secondary wing feathers are gray, with the first primary feathers having a white outer vane, and the wing edges are also white. The tertiary wing feathers are a lighter gray and have white spots at the tips, which are often absent in older birds. The eyes are reddish-brown. The beak and the plate behind the beak are white, with a slightly pinkish base. The legs are pale green. The tibia is tinged with orange-yellow.
Measurements:
Wing: 185 – 220 mm; Tail: 54 – 63 mm; Tarsus: 56 – 61 mm; Bill: 33 – 38 mm.
Distribution:
The species is distributed in Southern Europe, Northwest Africa, Southern Soviet Union, Central Asia, India, Northwest Mongolia, Northeast China, Korea, and Japan. During the winter, the species migrates south to North Africa, India, Indochina, Sumatra, and Java.
In Vietnam, during the winter, the species is found in the Northern plains, especially in the areas of Bac Ninh, Hai Duong, Ninh Binh, and the Red River and Thai Binh River estuaries, and occasionally in North Central Vietnam.