What is "vireo olivaceus"

Vireo \Vir"e*o\, n. [L., a species of bird.] (Zo["o]l.) Any one of numerous species of American singing birds belonging to Vireo and allied genera of the family Vireonid[ae]. In many of the species the back is greenish, or olive-colored. Called also greenlet.

Note: In the Eastern United States the most common species are the white-eyed vireo ( Vireo Noveboracensis), the red-eyed vireo ( Vireo olivaceus), the blue-headed, or solitary, vireo ( Vireo solitarius), the warbling vireo ( Vireo gilvus), and the yellow-throated vireo ( Vireo flavifrons). All these are noted for the sweetness of their songs.