It is a fairly polytypic species with a relatively complex taxonomy. . Its name Synallaxis comes from the Greek sunallaxis = change, which was assigned by Vieillot (1818) referring to characters that merited recognition as a different gender. The epithet azarae was established in honor of the Spanish military engineer and naturalist Felix Manuel de Azara.
It measures 15-17 cm and weighs 12-18 g. Both sexes similar. It has reddish-brown irises, olive-gray legs and a bill with a blackish upper jaw and a grayish lower jaw. Nominal breed has brownish-gray face, slightly paler superciliary, grayish-brown forehead and crown, occiput and nape dark rufous, and back to olive-brown supracaudal coverts. Its wings are mainly rufous chestnut with dark brownish remige tips and brownish-brown tail. It has a pale grayish chin and throat edges with darker feather tips and a sooty black triangular central throat patch with gray feathers margins. Its chest is dark brownish-gray, it has a paler, greyish belly with faint mottling, brownish flanks and undertail-coverts. The young individual has a brown crown and back, an inconspicuous throat patch, and pale brown wash underparts, mainly on the chest.
Very similar to the Silvery-throated Spinetail (Synallaxis subpudica) which has a slightly longer tail and grayish brown, not rufous. Pale-breasted Spinetail (Synallaxis albescens) has a shorter, brown tail, not ruff, and is generally found at lower elevations. The Slate Rastrojero (Synallaxis brachyura) has a slate gray face and upper parts.
Nine subspecies are recognized, of which only two are found in Colombia. The race S. a. elegantior is found in the Eastern Cordillera and differs from the nominal race because it is paler with poorly defined buff or greyish superciliary, white point in the loreal region and fulvo flanks. The middle breed is similar to the elegantior subspecies but with less contrasting gray superciliary, smaller loreal region point, greyish breast, paler and olive flanks.
It is distributed throughout the Andes from western Venezuela to northwestern Argentina. In Colombia it is distributed from 1600 to 3000 m above sea level (sometimes up to 900 m on the Pacific slope) in the Western mountain range to the height of Cali, the Central mountain range and the Eastern mountain range.
It lives in the understory and on the edges of humid montane forests and dwarf forests. Commonly found in bamboo growths, it uses secondary growth forests, regenerating clearings, bushes and ferns.
It feeds mainly on arthropods such as some moth larvae and to a lesser extent on seeds.
It is a monogamous species. In Colombia, individuals in reproductive condition have been registered from January to September in the Central and Eastern mountain ranges and a nest in March in PNN Cueva de los Guácharos. Also individuals in reproductive condition from February to March and nests in March and April in the Western Cordillera. Its nest is a bulky and elongated mass that it builds with twigs at low height on dense vegetation. It has a tunnel 30 to 40 cm long that connects the entrance to an internal bedroom, which is covered with soft plant material and sometimes with snake shedding. Commonly lays two eggs and up to 4 in Argentina.
It is a rather sneaky bird that is easier to hear than to see. It remains in pairs and is sometimes seen with mixed flocks. It forages in dense, low vegetation where it actively jumps in search of prey which it captures by gleaning on leaves, small branches and occasionally on dead leaves.
Sometimes the elegantior, ochracea, media and fruticicola races have been treated as a single species, as have the superciliosa and samaipatae races.
At the national and international level, it is classified as a species of least concern.