As its name suggests, the Cape Grassbird lives in areas of rank, tall grass as well as thick low-growing fynbos and stands of ferns, often on hillsides and in river valleys and usually near water. They are normally seen singly or in pairs. Cape Grassbirds follow an insectivorous diet, catching most of their food on the ground. Adults grow to 19cm in length and weigh between 26 and 34g.
Cape Grassbirds breed almost throughout the year, with a peak in spring and early summer. Pairs mate for life. The female builds the bowl-shaped nest of twigs, grass and leaves near the ground in a tussock of grass or a bush. The female incubates the clutch of 2 or 3 eggs for just over 2 weeks. After hatching, both parents feed the chicks, which fledge at around 2 weeks old.
The Cape Grassbird occurs only in South Africa, Lesotho, Swaziland and in a limited area on the border between Mozambique and Zimbabwe. In South Africa they are found in the Western and Eastern Cape, Kwazulu-Natal, Free State, Gauteng and the Highveld of Mpumalanga and Limpopo. The IUCN currently lists it as “Least Concern” but also cautions that the population of the Cape Grassbird is decreasing due to habitat destruction (threatened by agriculture, urbanisation and invasion by alien trees).