Azara's Spinetail
Synallaxis azarae
Azara's spinetail is 15 to 18 cm (5.9 to 7.1 in) long and weighs 12 to 18 g (0.42 to 0.63 oz). The sexes have the same plumage. Adults of the nominate subspecies S. a. azarae have a brownish gray face with a slightly paler supercilium. Their forehead and forecrown are dark grayish brown, their hindcrown and nape dark rufous, and their back, rump and uppertail coverts rich olive-brown. Their wings are mostly rufous-chestnut with dark brownish tips on their flight feathers. Their tail is dull chestnut-brown; the tail is graduated and the feathers have somewhat pointed tips. Voice: Azara's spinetail is quite vocal, repeating for minutes at a time a sharp "ket-kwééék", "pip-squeak", or "ka-kweeék". It also makes "scratchy, nasal 'prrt' notes", " 'kweek-kweek' notes", and a "low short 'chur' or 'trrt' ".
ID text from Wikipedia, CC BY-SA 4.0

Spix's Spinetail
Synallaxis spixi
Spix's spinetail is 16 to 17 cm (6.3 to 6.7 in) long and weighs about 12 to 15 g (0.42 to 0.53 oz). The sexes have the same plumage. Adults have a pale gray supercilium on an otherwise grayish brown face. Their crown is rufous and their back, rump and uppertail coverts dark brown. Their lesser wing coverts are rufous, their median and greater wing coverts dark brown with wide rufous edges, and their flight feathers dark brown. Their tail is dark brown; it is graduated and the central feathers have pointed tips. Voice: The song of Spix's spinetail has been described as "a five syllable phrase, last four notes with bubbling quality: sweet! bee bee bee bee . . . . . .sweet! bee bee bee bee . . . ." and a repeated "wee'tiddledidee....wee'tiddledidee". Another vocalization is a "4- or 5-noted 'wuh-wididit' ".
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Azara's Spinetail and Spix's Spinetail.