The vireos make up a family, Vireonidae, of small to medium-sized passerine birds found in the New World (Canada to Argentina, including Bermuda and the West Indies) and Southeast Asia. The family contains 62 species and is divided into eight genera. "Vireo" is a Latin word referring to a green migratory bird, perhaps the female golden oriole, possibly the European greenfinch.

They are typically dull-plumaged and greenish in color, the smaller species resembling wood warblers apart from their heavier bills. They range in size from the Chocó vireo, dwarf vireo and lesser greenlet, all at around 10 cm and 8g, to the peppershrikes and shrike-vireos at up to 17 cm and 40g.

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