Adult Plumage:
- Summer Plumage: Forehead, eyebrows, and supercilia white. Crown, nape, crest, back, and shoulders slate-black with a bluish sheen. Chin, throat, foreneck, center of the breast, abdomen, and undertail coverts white. Remaining plumage ash-gray, slightly paler on the neck and darker on the wings and tail.
- Winter Plumage: Bluish sheen on the plumage is less pronounced than in summer.
Juvenile Plumage:
- First Summer Plumage: Similar to adult plumage, but the steel-blue sheen is paler. Dorsal surface tinged with brown, with pale buff feather shafts.
- First Winter Plumage: Lacks steel-blue sheen, or it is very faint. Dorsal surface brown with buff streaks; these streaks widen and fade on the wing coverts. Primary and secondary flight feathers ash-gray with white tips. Underparts white or white tinged with buff, with dark brown streaks.
Other Characteristics:
- Eyes: Red.
- Bill: Black, with the base of the maxilla and most of the mandible pale yellowish-green.
- Bare Skin Around Eyes and Legs: Pale yellowish-green.
- Breeding Season: Bill becomes darker, legs slightly reddish-brown, and facial skin reddish-black.
Measurements:
- Wing: 250 – 304 mm
- Tail: 79 – 107 mm
- Tarsus: 69 – 73 mm
- Bill: 61 – 75 mm
Distribution:
Found in Southern and Central Europe, Africa, Central Asia, India, Sayansk, Myanmar, Thailand, Laos, Cambodia, Vietnam, China, Korea, Japan, Malaysia, Borneo, Sumatra, and Java.
In Vietnam, found throughout all regions, but with higher densities in the lowlands.