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 belli arizonaei, 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. They are known in Mexico as vireo de Bell.

Bell’s Vireo is small in stature with short, rounded wings, with a long tail. 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. The sexes are similar in size and appearance.

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 forage primarily on insects. They are known for being active while foraging in dense thickets and also for their songs. During the breeding season, the males become highly territorial. They have a lifespan of nine years.

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 are found in Western Mexico from within the Pacific Slope of Baja California Sur, Chihuahua, Jalisco, Michoacán, Sinaloa, and Sonora.

From a conservation perspective, Bell’s Vireo is currently categorized by the IUCN as 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 and are currently the subject of significant research and conservation promoting the protection of avian biodiversity.