Bell’s Vireo, Vireo belii
Bell’s Vireo, Vireo belii arizonae. Photograph taken within a residential community in Alamos, Sonora, April 2018. Photograph and identification courtesy of David F Smith, Alamos, Sonora.
Bell’s Vireo, Vireo belii arizonae. Photograph taken within a residential community in Alamos, Sonora, April 2023. Photograph and identification courtesy of David F Smith, Alamos, Sonora.
Background and Identification
Bell’s Vireo, Vireo belli arizonae, is one of four subspecies of Bell’s Vireo, all four of which winter in Mexico. They are a member of the Vireonidae Family of Vireos, Shrike-Babblers, and Erpornis, which has sixty-three members placed in eight genera, and one of thirty-three global members of the Vireo Genus. Bell’s Vireos are insectivores, indicative that they only consume insects. They have a lifespan of nine years. They are known in Mexico as Vireo de Bell.
Bell’s Vireo is small in stature with short, rounded wings, with a long tail. The length of this species varies from 11.5 cm (4.5 inches) to 12.5 cm (4.9 inches) and they weigh between 7 g (0.25 oz) and 10 g (0.35 oz). Their bills are short, straight, and blunt-tipped. They are a drab gray to green in color above transitioning to white to yellow below. Their breast is unstreaked, they have a faint white eye ring and two pale wing bars of which the lower bar is more prominent. There are slight geographical variations present, individuals that breed east of western Texas are brighter and more colorful overall than the birds that breed in the southwest. Some intermediates occur within their range as well. This species is known for its small stature and extremely active tail flicks and bobs while foraging in dense forests. The sexes are similar in size and appearance. Most breeding pairs are socially monogamous, meaning that some males and females may switch mates between nest attempts. During the breeding season, the males become highly territorial.
Habitat and Geographical Range
Bell’s Vireo is found within dense vegetation of riparian areas, brushy fields, young second-growth forests or woodlands, and mesquite brushlands. They breed in Northern Mexico and are migratory, wintering in Southern Mexico and Baja California. They are found at elevations up to 1,800 m (5,900 feet). They prefer areas near large bodies of water or rivers, and observers will not find this species in areas void of woody plants, open desert scrub, or elevations higher than 1,800 m (5,900 feet).
Bell’s Vireo is found throughout Mexico at certain times during the year with the exception that they are absent from around the Yucatán Peninsula. The arizonae subspecies is found in Western Mexico from within the Pacific Slope of Baja California Sur, Chihuahua, Jalisco, Michoacán, Sinaloa, and Sonora.
Common Misidentifications
A commonly misidentified species similar to Bell’s Vireo is the Warbling Vireo, Vireo gilvus. Bell’s Vireo is smaller and slimmer and has white bars on its wings.
Conservation Status
From a conservation perspective, Bell’s Vireo is currently considered to be of Least Concern with stable, widely distributed populations. Their nests are heavily parasitized by the Brown-headed Cowbird, Molothrus ater, which has caused significant declines in their populations.