Adult Bird:
Similar to the subspecies Apus pacificus pacificus, but with a darker back and more greenish iridescence. The black markings on the chin and throat are broader. In this subspecies, the first primary feather is the longest, or the first and second primaries are nearly equal in length; in the subspecies pacificus pacificus, the second primary feather is the longest.
Dark brown eyes. Bill and feet are black.
Measurements:
- Wing: 162 – 172 mm
- Tail: 67 – 73 mm
- Tarsus: 11 mm
Distribution:
This subspecies is distributed in southern China, Assam, Thailand, and Indochina.
In Vietnam, they nest in high mountain caves in many regions. They are occasionally seen flying in flocks even in the plains (Hanoi).