The Grey-rumped Treeswift occurs in Southeast Asia and its islands. It uses perches and catches insects in flight.
A breeding adult male has a glossy dark-green cap with a raised crest, brick-red ear patches, and a conspicuous pale-gray rump.
It launches from a perch to catch flying insects. Communal winter roosts have also been reported for this species.
Its small half-saucer nest on the side of a thin branch contains moss, bark flakes and feathers bound with saliva. It lays one white egg.
An incubating adult grips the nest edge while resting on the branch, bringing its brood patch against the egg. Both sexes incubate and brood the chick.
An extinction-risk assessment has not been added yet.