Sooty-fronted Spinetail

The sooty-fronted spinetail is 14 to 16 cm (5.5 to 6.3 in) long and weighs 11 to 17 g (0.39 to 0.60 oz). The sexes have the same plumage. Adults have a thin brownish line through the eye on an otherwise brownish gray face. Their forecrown ("front") is dark gray-brown, their hindcrown and nape dark rufous, and their back, rump and uppertail coverts brown with a rufescent tinge. Their wing coverts are dark rufous and their flight feathers tawny-rufous with dusky tips. Their tail is dark rufous with some darker inner webs on the innermost pair of feathers; the tail is graduated and the feathers have slightly pointed tips. Their chin is whitish and their throat grayer; the lower throat feathers has a blackish crescent with pale speckles. Their breast is grayish brown, their belly paler than the breast, and their flanks and undertail coverts browner than the breast and belly. Their iris color is highly variable, their maxilla blackish to dark gray, their mandible gray to pale gray (sometimes with a blackish tip), and their legs and feet olive-gray to greenish gray. Juveniles have a brownish gray crown and an ochraecous wash on their underparts. There is clinal variation in adults, with brighter plumage in the northeast becoming duller in the southwest.

The sooty-fronted spinetail is found from northeastern Brazil (Maranhão to Rio Grande do Norte) southwest in a wide swath through Brazil, eastern Bolivia, most of Paraguay, essentially all of Uruguay, and into Argentina to northern Buenos Aires Province. It inhabits a variety of semi-open landscapes such as gallery forest, the edges of scrubby or deciduous forest, thorn-scrub, woodlands, and bushy savanna.

The sooty-fronted spinetail's diet is not known in detail but includes beetles. It usually forages in pairs, apparently gleaning prey from foliage and small branches and sometimes the ground. It usually stays below about 2 m (7 ft) of the ground.