The buff-bellied hermit is long and weighs. It has metallic green upperparts and ochre to buff underparts. The innermost pair of tail feathers are longer than the others and all have white tips.
The buff-bellied hermit's breeding season has not been conclusively determined, but observations hint that it is during the November to April wet season. Malescongregate at leks. The nest has not been described.
Vocalization
The buff-bellied hermit's song is "a continuously repeated high-pitched phrase...a short note followed by a rising one...or a short note followed by a falling one 'tsi-tsew', up to a more complex 'tsi-tsi-tseeé-euw'."
Status
The IUCN has assessed the buff-bellied hermit as being of Least Concern, though its population size is unknown and believed to be decreasing. It is locally common but "oorly known, and should perhaps be classed as Data Deficient."