- 4.3–4.7 in
- 7.1 in
- 0.2–0.4 oz
- Viréo de Bell (French)
- Vireo Aceitunado, Vireo Oliva, Vireo de Bell (Spanish)
- The Bell's Vireo is the most yellow in the easternmost part of its range, and it gets progressively grayer to the west. The "Least" Bell's Vireo of California and northern Baja California is the grayest, with little yellow or green in its plumage.
- A pair of Bell's Vireos may forage together at times during the breeding season, progressing upward in a spiral, gleaning insects from the vegetation.
- The Bell's Vireo has not been observed drinking water. It may be able to obtain all that it needs from its food.
- The oldest recorded Bell's Vireo was at least 8 years, 2 months old, when it was recaptured and rereleased during a banding operation in California.
Dense, low, shrubby vegetation, generally early successional stages in riparian areas, brushy fields, young second-growth forest or woodland, scrub oak, coastal chaparral, and mesquite brushlands, often near water in arid regions.
Insects and spiders.
- Clutch Size
- 3–5 eggs
- Egg Description
- White with sparse spotting.
- Condition at Hatching
- Helpless and naked.
Open bag-like or basket-like cup of grass, straw-like stems, plant fibers, small skeletonized leaves, paper, and strips of bark fastened with spider silk; lined almost invariably with fine, brown or yellow grass stems. Outside decorated with spider egg cases. Suspended from forks of low branches of small trees or shrubs.
Gleans from leaves, twigs, and branches. Sometimes hovers while feeding.
Bell's Vireo populations were stable between 1966 and 2014, according to the North American Breeding Bird Survey. However, one subspecies, the "Least" Bell's Vireo of California is considered endangered, primarily from loss of riparian habitat and cowbird parasitism. This subspecies is declining throughout its range, and is on the 2014 State of the Birds Watch List, which lists bird species that are at risk of becoming threatened or endangered without conservation action. Partners in Flight estimates a global breeding population of Bell's Vireo of 4.6 million with 77% breeding in the U.S., and 81% spending some part of the year in Mexico. They are listed as a Tri-National Concern species, and rate a 15 out of 20 on the Continental Concern Score.