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. Their chin is buff-white and their throat buff. Their breast is light brown with faint paler streaks, their belly plain light brown, and their flanks and undertail coverts a slightly darker brown. Their iris is dark reddish brown, their maxilla black, their mandible dull horn to silvery horn, and their legs and feet dull greenish olive or grayish. Juveniles have more grayish upperparts than adults, with a variable ochraceous wash and faint mottling on their underparts. Subspecies C. v. apurensis is the darkest subspecies overall, especially on the crown, wings, and tail. C. v. foxi has darker rufous upperparts than the nominate. C. v. reiseri is paler than the other subspecies but with more rufescent upperparts; its underparts are more buffy than the nominate's and have no streaking.

The subspecies of the rusty-backed spinetail are found thus:

C. v. apurensis: western Venezuela's Apure state C. v. vulpina: northeastern Colombia, central and southern Venezuela, western Guyana, northern and central Brazil, extreme eastern Bolivia, and extreme northeastern and eastern Paraguay (but see below) C. v. foxi: central Bolivia's Cochabamba Department and possibly Beni Department C. v. reiseri: northeastern Brazil The South American Classification Committee of the American Ornithological Society has only sight records from Guyana and so classes the species as hypothetical in that country. The rusty-backed spinetail inhabits a variety of landscapes, all of which are on or near water. These include gallery forest, scrub on river islands, thickets along rivers, várzea forest, and shrubby areas around lakes and streams. In elevation it ranges from near sea level to 400 m (1,300 ft).

The rusty-backed spinetail feeds on arthropods. It typically forages singly or in pairs and occasionally joins mixed-species feeding flocks. It mostly feeds in the forest's lower levels but is known to feed higher in riverside forest. It acrobatically gleans prey from bark and dead leaves (and occasionally live ones) while hitching along small branches.