Formerly classified in the genus Schizoeaca. It is a difficult to see bird with a fairly long tail that lives in the high Andean mountains from Venezuela to Peru. Its name Asthenes comes from the Greek and means weak or insignificant. The epithet fuliginosa comes from the Latin fuliginosus = sooty.
It measures 18 to 20 cm and weighs 14 to 20 g. Both sexes are similar. It has brown to grayish irises, grayish legs and a bill with a black to gray upper jaw and a dark lower jaw with a light base. Nominal race has inconspicuous grayish superciliary, whitish eye ring, face and loreal region blackish to dark brown, crown and upperparts of dark reddish brown color. Its wings have a brighter tint, it has a long, graduated and forked tail with frayed-looking beards. It has a white spot on the chin and the rest of the grayish underparts with a brownish tint on the flanks.
It could be confused with the Streak-backed Canastero (Asthenes wyatti) and the Many-striped Canastero (Asthenes flammulata), both with striated upper parts. The Andean Tit-Spinetail (Leptasthenura andicola) has a shorter bill and a striated body.
Four subspecies are recognized: A. f. fuliginosa, A. f. fumigata, A. f. peruviana and A. f. plengei. In Colombia the nominal breed is found in the eastern Andes from north to south to Cundinamarca. The fumigata breed is found in the central Andes and is distinguished by darker back and more brown and less gray underparts.
It is found in the Andes from western Venezuela to central Peru. In Colombia it is found from 2300 to 3600 m above sea level in the Eastern Cordillera from the south of the department of Norte de Santander south to the south of Cundinamarca and in a small region of southern Santander. Also in the Central mountain range in the south of the department of Caldas, east of Risaralda and Quindío, north of Tolima, south of the department of Huila, southeast of Cauca, east of Nariño and west of Putumayo.
It inhabits the transition zone from dwarf forest to páramo, in forest edges, dense undergrowths and tall tangled grasses.
It feeds mainly on arthropods and sometimes on fruits.
In Colombia, individuals in reproductive condition have been recorded from July to September in the Eastern Cordillera. Also a nest in August in the Chingaza National Natural Park. Its nest is a spherical structure built with moss, grass and frailejon wool 13 cm from the ground on grass. The size of its position is 2 white eggs.
Remains alone, in pairs and rarely in mixed flocks. It captures its prey by gleaning in the foliage and in small branches of the understory, sometimes performing acrobatic maneuvers. When alarmed, it holds its tail upright.
Previously classified in the genus Schizoeaca whose members were considered by some authors as conspecific. However, it was found that they do not form a monophyletic group and are highly polyphyletic with respect to Asthenes. The present species is parapatric with respect to A. griseomurina whose range is found in the middle of the northern races (fuliginosa and fumigata) and those of the south (peruviana and plengei). Asthenes griseomurina is probably more closely related to the northern races of A. fuliginosa than they are to each other.
State of conservation
At the national and international level, it is classified as a species of least concern.