In Amazonia, Russet-backed Oropendola is the most abundant oropendola species. They also occur in the humid subtropical forest of the both Andean slopes, where they are the only oropendola. This species has three subspecies: P. a. astrocastaneus, on the western Andean slope, P. a. alfredi in the eastern Andean subtropical forest, and P. a. angustifrons in Amazonia. These subspecies differ primarily in bill and face coloration and vocalizations. Although somewhat uncommon in the subtropics, Russet-backed Oropendola is a prominent species in the lowlands. There, their colonies of long, hanging basket nests are ubiquitous in riparian and second growth habitats. Their voice is an explosive series of liquid, burbling notes.