The Yellow-rumped Marshbird is an icterid of open grassland and wet habitats in southeastern South America. A nest study in northeastern Argentina and Paraguay recorded birds other than the parents helping raise chicks.
It is about 24 cm long. The head and chest are dark brown, the back olive-brown, and the rump, parts of the wings, and underparts yellow. The bill and legs are black, and the iris is brown.
Birds other than the parents fed chicks or defended nests at eight of nine monitored nests. The paper also describes ground foraging for arthropods and small vertebrates.
An extinction-risk assessment has not been added yet.