A chunky, streak-backed warbler with a rusty head and wings, a ragged rufous tail, and black moustache stripes. It avoids woodland and trees, preferring rank areas with long grass, scrubby edge, and wet heathland (fynbos). It hops and clambers through dense brush and thickets, then flies low on rapidly-beating wings in labored flight to the next bush, immediately diving into cover. But it will also perch on prominent tall shrubs, like proteas, and sing its melodious tinkling jumbled song that starts softly and gets progressively louder. It also has a distinctive flat mewing “meeeeep” call. The Moustached Grass-Warbler is similar to the Cape Grassbird, but it has a plain unstreaked back, a broad black tail, and a pale eye.