The Russet-backed Oropendolas (Psarocolius angustifrons) are endemic to the wooded highlands of the northern and central Andes and the Venezuelan Coastal Range, and in lowlands of the western Amazon. It is generally common and widespread.
Both genders look alike, except the males are generally larger than females.
The Russet-backed Oropendolas plumage is mostly olive and brown. The rectrices (the long flight feathers of the tail are contrastingly yellow.
The lowland nominate subspecies has a black bill, while the highland subspecies all have pale bills.
These two have historically been regarded as separate species. However, since they hybridize freely, all major authorities regard them now as a single species.