Swiftlet

Description:

Swiftlets are notoriously difficult at a distance. There are 5 species possible here but Bornean is a montane species so unlikely..
Glossy has a whitish mid-belly and glossy deep blue upperparts which cannot be seen from this angle and an almost square tail.
Black-nest has pale throat and belly with a central darker patch, a whitish rump and almost square tail. The nest is dark grey.
Edible-nest has a plain brown underside, a barely noticeable pale rump patch and a well-notched tail. The nest is white.
Mossy-nest is overall dark with a pale underside and a slightly notched tail. The nest is a mossy green/brown with almost golden spots near the top.
The latter 3 are best separated by their nests and location around areas where there are large caves though they probably range far and wide.

Habitat:

Equatorial lowland rainforest.

Notes:

I am leaning towards Mossy-nest Swiftlet (Aerodramus salangana) for these but my only certainty is it is not Edible-nest Swiftlet.