The Warbling Vireo, Vireo gilvus, is a small songbird. Adults are 12 cm long and weigh 12 g. They are mainly olive-grey on the head and upperparts with white underparts; they have brown eyes and the front of the face is light. There is a white supercilium. They have thick blue-grey legs and a stout bill. Western birds are generally smaller.
Edward Howe Forbush Useful Birds and Their Protection (Boston, MA: Massachusetts State Board of Agriculture, 1907)