The Bell's Vireo (Vireo bellii) is a small North American songbird. It is 4-3/4 to 5 inches (12-13 cm) in length, dull olive-gray above and whitish below. It has a faint white eye ring and faint wing bars.
The Bell's Vireo makes a well-camouflaged nest but when found the bird will stand its ground against intruders. Cowbirds use Bell's Vireo nests as their own nurseries.
This bird was named by Audubon for John Graham Bell, who accompanied him on his trip up the Missouri River in the 1840s.
The Least Bell's Vireo (Vireo bellii pusillus), an endangered subspecies in Southern California, has been an important factor to development projects. Considerable cost has been added to some construction projects, or projects have been blocked altogether, to protect Least Bell's Vireo habitat. The decline of the Least Bell's Vireo is mostly due to an increase in grassland, probably due to wildfires. The grassland is favorable to Cowbirds which lay their eggs in Bell's Vireo nests.