Adult Plumage:
Summer: Head, neck, upper back, and underparts to undertail coverts are velvety black. Lesser wing coverts and wing edges are white, transitioning to silvery-gray on the median wing coverts and gray on the greater wing coverts. The first and second primary feathers are dark brown with a long white streak at the base, extending nearly to the tip of the first feather; the third primary feathers are dark gray with a white streak at the base like the previous two feathers; the other primary feathers are silvery-gray on the outer vane and darker on the inner vane.
Winter: Very similar to Chlidonias hybrida swinhoei, differing only in smaller size. Eyes are dark brown. Beak and legs are red, becoming slightly darker in winter.
Measurements:
- Wingspan: 191 – 215 mm
- Tail: 69 – 75 mm
- Tarsus: 20 – 21 mm
- Bill: 24 – 27 mm
Distribution:
This species of tern is distributed in temperate climates of Europe and Asia, migrating south to India, Sri Lanka, Burma, China, Indochina, and Malaysia in winter.
Vietnam: This species is common along the coast and at the mouths of large rivers in central Vietnam.