Vireo, a small bird native to the Americas. Most species live permanently in the tropics, but about 25 of the 40 species migrate to North America in spring. Vireos are 4 to 6 inches (11 to 15 cm) long. Their backs are grayish or olive green, their underparts white, usually tinged with yellow at the sides.Vireos are small birds with gray or green plumage tinged with yellow at the sides.
Vireos feed chiefly on insects. They spend most of their time in trees, methodically searching for insects under leaves and in openings in the bark. While seeking their prey, they sing almost without stopping. They are of great service in destroying insect pests in forests, orchards, and parks.
Vireos make baglike nests of grasses, strips of bark, rootlets, hair, and other materials. The nests are usually lined with moss or other soft materials, and are often bound with spider web or caterpillar silk. The female lays three to five white eggs spotted with brown, black, lilac, or purple.
The warbling and yellow-throated vireos have the sweetest voices. The red-eyed and white-eyed vireos are most widely distributed.
The warbling vireo is Vireo gilvus; the yellow-throated, V. flavifrons; the red-eyed, Vireo olivaceus, the white-eyed, V. griseus Vireos form the vireo family, Vireonidae.