North-central Argentina (Chaco and Corrientes south to Córdoba, Mendoza, La Pampa and Buenos Aires), extreme south-eastern Brazil (southern Rio Grande do Sul) and Uruguay.
 
Rarity Status
Currently this species is not classified as a rarity in this country OR information has not been updated.
Population
Estimated population is unknown (2010) and decreasing.
Status NT
Habitat destruction and degradation through marsh drainage and the drying effects of Eucalyptus and Pinus spp. plantations, are the main threats.
For more information see BirdLife International Species Factsheet.
Bay-capped Wren-Spinetail (Spartonoica) [XC510847]
by JAYRSON ARAUJO DE OLIVEIRA from Trilha do Talha-Mar, PARNA Lagoa do Peixe, Tavares, Rio Grande do Sul, Brazil (song)
Bay-capped Wren-Spinetail (Spartonoica) [XC52641]
by Bernabe Lopez-Lanus from Tapalque, Buenos Aires, Argentina (song)
Subspecies
No subspecies.
Placed in Synallaxis by some authors, but thought to be more closely related to Asthenes or Leptasthenura by others.
Similar Species
Three sympatric species (Hudson's Canastero (Asthenes hudsoni), Stripe-crowned Spinetail (Cranioleuca pyrrhophia) and Grass Wren (Cistothorus platensis)) also found in marshes are basically similar, though all lack the distinctive rufous crown.
References
See References.