The rufous-capped, grey-cheeked, and chestnut-headed (N. amaurocephala) nunlets form a superspecies.

The chin and breast are reddish orange, the flanks a paler rufous, and the central underparts whitish.

The bill is mostly silvery blue, the eye brown with a bare reddish ring around it, and the feet dark brownish gray.

[6] The subspecies of rufous-capped nunlet are distributed thus:[2][6] The species inhabits the undergrowth and subcanopy of a variety of landscapes, including terra firme, secondary, and transitional forest; forest along rivers and streams, and igapó.

The rufous-capped nunlet's song is a "long series (13–30 notes) of sharp, clear, short, upward-inflected whistles , 'fwick!-fwick!