Mistletoes and Golden-rumped Euphonia seem to be married in an unbreakable bond. The parasitic mistletoes are a preferred food source for this colorful euphonia which disperses its seeds on top of tree branches that will later be parasitized. Widely but disjunctly distributed in South America it is a frequent member of mixed species flocks throughout its geographic range. Migratory movements are not well understood, and while eastern populations appear to be resident or with minor altitudinal movements, the Atlantic Forest subspecies migrates to the west and downslope from Brazil into Paraguay and Argentina during winter to keep feeding on mistletoes. It is the only euphonia in its range that combines a dark throat, a golden rump and an electric-blue cap. The fast and hasty vocalizations are also diagnostic.