The Tasmanian Thornbill is a medium sized thornbill very similar to the Brown Thornbill A. pusilla. The two are best told apart by the adage that the Tasmanian Thornbill "wears the white underpants". The adult Tasmanian Thornbill is olive-brown above with rufous-brown suffusion to the forehead; dull rufous-brown rump-patch and prominent rufous brown panel on folded wings. The underparts are off-white with diffuse fine dusky mottling on chin, throat and breast, and clean white undertail-coverts. Juvenile birds are similar to adults but newly fledged birds are fluffier.