This species is similar to the Satin Swiftlet (now split from Glossy Swiftlet) but has more pointed wings and lacks glossy blue upperparts. In New Caledonia also differs in having a narrower white rump, ill-defined paler lower breast and belly, no white on underwing, and no white tail-spots. Canon PowerShot SX60.
References:
Chantler, P. & Boesman, P. (2019). White-rumped Swiftlet (Aerodramus spodiopygius). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55273 on 13 December 2019).
Dutson, G. (2011) Birds of Melanesia, Christopher Helm, London.