Slaty spinetail

The slaty spinetail or slaty castlebuilder, (Synallaxis brachyura), is a passerine bird in the Furnariinae subfamily of the ovenbird family Furnariidae. It is found from Honduras south to Peru.

The slaty spinetail is 14 to 16 cm (5.5 to 6.3 in) long and weighs 16 to 21 g (0.56 to 0.74 oz). The sexes have the same plumage. Adults of the nominate subspecies S. b. brachyura have a grayish supercilium on an otherwise darker gray face. Their crown and nape are deep rufous-chestnut, their back is dark sooty brown to slate-brown, and their rump and uppertail coverts are slightly browner than the back. Their wing coverts and base of their flight feathers are deep rufous-chestnut and the rest of the flight feathers are dark brown. Their tail is the same brown as the rump and uppertail coverts; it is long and the feathers lack barbs at their tips, giving a spiny appearance. Their throat is blackish, their breast and sides dark sooty brown, their belly a paler and grayer brown, and their flanks and undertail coverts browner than the belly. Their iris is reddish brown to orange-brown, their maxilla black to gray, their mandible gray to blue-gray, and their legs and feet olive-gray, gray, or blue-gray. Juveniles have a gray crown and nape and compared to adults have paler upperparts, duller wing coverts, and more olivaceous underparts.

Subspecies S. b. nigrifumosa has a darker brown back, darker rufous crown and wings, and darker gray underparts than the nominate. S. b. griseonucha is darker than the nominate but paler than nigrifumosa. S. b. caucae has a paler crown, a grayer back, and paler grayish olive rump and uppertail coverts than the nominate.