A tiny bird of montane forest canopy. Medium gray above and clean white below with a black bill and dark eye. Forages very actively in small single or mixed species flocks and often hovers to catch insects. Similar to Papuan Thornbill and Brown-breasted Gerygone, but Gray Thornbill is distinctly gray rather than brown above. Voice very similar to Brown-breasted Gerygone and birds even respond those calls. Song, a descending series of high-pitch, slurred notes. Call, high-pitch chips.