Rusty-backed Spinetail

The rusty-backed spinetail is 15 to 16 cm (5.9 to 6.3 in) long and weighs 14 to 17 g (0.49 to 0.60 oz). The sexes have the same plumage. Adults of the nominate subspecies C. v. vulpina have a buff supercilium and a narrow dark brownish line behind the eye on an otherwise light brownish face that has faint streaks and spots. Their forehead is brown, their crown and back reddish chestnut, their rump brown, and their uppertail coverts reddish chestnut. Their tail is also reddish chestnut. Their wings are reddish chestnut with duskier tips on the flight feathers. Voice: The rusty-backed spinetail's song has variously been described as "a rapid series of emphatic notes gradually accelerating but fading, lasting c. 2·5–3 seconds, 'ch-ch-ch-chchchchchewewewewewew' ", "a series of descending, complaining notes 'scew-scew-scew- -", and a "rattly trill, descending, last 2-3 secs". Its call is "a soft, nasal, rising 'choy', 'choy-choy' or 'kuee-kweek' ".