Chivi Vireo is one of the most widespread and common passerines of South America. This species consists of a complex mosaic of resident and migratory populations, however. Not only is there seasonal overlap, in the austral winter, between some resident populations and wintering populations from southern South America, but during the boreal winter there also is overlap between the same resident Chivi Vireos and wintering Red-eyed Vireos (Vireo olivaceus) from North America! For many years Chivi and Red-eyed vireos were considered to be the same species; this is understandable, given that they are very similar in appearance, but phylogenetic analysis of DNA sequence data reveals that Chivi is more closely related to Black-whiskered Vireo (Vireo altiloquus) than it is to Red-eyed. The general biology of Chivi Vireo probably is very similar to that of Red-eyed Vireo but, despite its abundance, Chivi Vireo is much less well studied.