Spix's Spinetail

Spix's spinetail is 16 to 17 cm (6.3 to 6.7 in) long and weighs about 12 to 15 g (0.42 to 0.53 oz). The sexes have the same plumage. Adults have a pale gray supercilium on an otherwise grayish brown face. Their crown is rufous and their back, rump and uppertail coverts dark brown. Their lesser wing coverts are rufous, their median and greater wing coverts dark brown with wide rufous edges, and their flight feathers dark brown. Their tail is dark brown; it is graduated and the central feathers have pointed tips. Their throat is grayish white; the lower throat feathers are black with grayish edges. Their breast is brownish gray, their belly a paler brownish gray, and their flanks and undertail coverts browner. Their iris is reddish brown to pale orange, their maxilla black, their mandible gray, and their legs and feet gray to greenish gray. Juveniles have a grayish brown crown, ochraceous brown underparts, and a less distinct throat patch than the nominate.

Spix's spinetail is found from Minas Gerais and Espírito Santo in southeastern Brazil south through eastern Paraguay and essentially all of Uruguay into Argentina as far as Buenos Aires Province. It inhabits a wide variety of landscapes in the Atlantic Forest biome, where it tends to stay low in dense undergrowth. Examples include fields and pastures, gallery forest, campo rupestres, restinga, savanna, and brushy second growth. In elevation it ranges from near sea level to 2,200 m (7,200 ft) though in Brazil its maximum is 2,050 m (6,700 ft).

The diet of Spix's spinetail is not known in detail but includes insects. It typically forages in pairs, usually in the understorey and sometimes on the ground. It usually stays within about 5 m (16 ft) of the ground but has been observed feeding significantly higher.