Red-eyed Vireo (Vireo olivaceus) Science Article 4
One of the most enduring puzzles in the systematics of New World birds concerns the relationships and taxonomic status of forms in the Red-eyed, Yellow-green and Chivi Vireo complex. In recent decades, the latter two taxa have been treated either as distinct species (A.O.U. 195 7, Hamilton 1962) or as races of the Red-eyed Vireo (Hamilton 1958, Barlow 1980, A.O.U. 1983). Arguments for specific status of the Yellow-green Vireo have stated that this form has a wing formula (Eisenmann 1962) and advertising song (Borror 1972) distinctive from those of the Red-eyed Vireo and Chivi Vireo, and have emphasized the lack of definitely intermediate specimens between flavoviridis and either other form.
NED K. JOHNSON AND ROBERT M. ZINK, Wilson Bull., 97(4), 1985, pp. 421-435