Bell's vireo

File:Least Bell's Vireo USGS WERC.jpg

Least Bell's vireo with leg band, grasped in human hand.

Bell's vireo (Vireo bellii)<ref name=BirdLife/> is a songbird that migrates between a breeding range in Western North America and a winter range in Central America. It is dull olive-gray above and whitish below. It has a faint white eye ring and faint wing bars.

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) is an endangered subspecies in Southern California. Consideration of Bell's vireo has been a factor in several land development projects, to protect least Bell's vireo habitat. The decline of the least Bell's vireo is mostly due to a loss of riparian habitat.

Description

Measurements:<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

• Length: 4.5–4.9 in (11.5–12.5 cm)
• Weight: 0.3–0.3 oz (7.4–9.8 g)
• Wingspan: 6.7–7.5 in (17–19 cm)

Subspecies

• Least Bell's vireo, V.b. pusillus (southern California)<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref><ref name=":0">Kus, B., S. L. Hopp, R. R. Johnson, B. T. Brown, and B. M. Reiley (2022). Bell's Vireo (Vireo bellii), version 2.0. In Birds of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.belvir.02</ref>

• Arizona Bell's vireo, V.b. arizonae (southwestern United States, northern Mexico)<ref name=":0" />
• V.b. medius (southwestern Texas, Mexico)<ref name=":0" />
• V.b. belli (central and midwestern United States to central Mexico)<ref name=":0" />

Behavior and ecology

In its breeding range, Bell's vireo often uses dense shrubbery in riparian areas or otherwise near water.<ref name=":0" /> Willow trees (Salix spp.) are a favored nesting species for all four subspecies of Bell's vireo,<ref>Bent, A. C. (1950). Life Histories of North American Wagtails, Shrikes, Vireos, and Their Allies. United States National Museum Bulletin 197:182–214.</ref><ref>Byre, V. J. (2004). Bell’s Vireo (Vireo bellii). In Oklahoma Breeding Bird Atlas (D. L. Reinking, Editor), University of Oklahoma Press, Norman, OK, USA. pp. 256–257.</ref> though in western areas mesquite and seep-willow (Baccharis salicifolia) are frequently used.<ref>Averill-Murray, A., and T. E. Corman (2005). Bell’s Vireo, Vireo bellii. In Arizona Breeding Bird Atlas (T. E. Corman and C. Wise-Cervais, Editors). University of New Mexico Press, Albuquerque, NM, USA. pp. 338–339.</ref><ref>Grinnell, J., and A. H. Miller (1944). The distribution of birds of California. Pacific Coast Avifauna 27:1–608.</ref>

Bell's vireos construct a hanging nest suspended between the ends of low tree branches.<ref name=":0" /> Bell's vireo nests are often parasitized by brown-headed cowbirds, reducing overall nest success.<ref>Template:Cite journal</ref>

California subspecies

Historically, the least Bell's vireo was a common to locally abundant species in lowland riparian habitat, ranging from coastal southern California through the Sacramento and San Joaquin Valleys as far north as Red Bluff in Tehama County. Populations also occurred in the foothill streams of the Sierra Nevada and Coast Ranges, and in Owens Valley, Death Valley, and scattered locations in the Mojave Desert. Least Bell's vireos winter in Baja California Peninsula. Unlike during the breeding season, they are not limited in winter to willow-dominated riparian areas, but occupy a variety of habitats including mesquite scrub within arroyos, palm groves, and hedgerows bordering agricultural and residential areas. At the time of endangered species listing by the U.S. Fish and Wildlife Service in 1986, it had been extirpated from most of its historic range, and numbered just 300 pairs statewide. Populations were confined to eight counties south of Santa Barbara, with the majority of birds occurring in San Diego County. In the decade since listing, least Bell's vireo numbers have increased six-fold, and the species is expanding into its historic range. In 1998, the population size was estimated at 2,000 pairs. Nesting least Bell's vireos have recolonized the Santa Clara River in Ventura County, where 67 pairs nested in 1998, and the Mojave River in San Bernardino County. The northernmost reported sightings in recent years is of a nesting pair of least Bell's vireos near Gilroy in Santa Clara County in 1997 and in the upper Carneros Creek watershed east of Highway 101 in northern Monterey County in 2001.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Roughly half of the current least Bell's vireo population occurs on drainages within Marine Corps Base Camp Pendleton in San Diego County, particularly in the lower Santa Margarita River.<ref name=Kus/>

External links

• Bell's Vireo Species Account - Cornell Lab of Ornithology
• Bell's Vireo - Vireo bellii - USGS Patuxent Bird Identification InfoCenter
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• Bell's Vireo synopsis - Wisconsin Department of Natural Resources
• Article on the Chino Hills oil spill of 1994 and its effect on the environment (including Least Bell's vireo) - U.S. Fish and Wildlife Service - Pacific Region
• Video of Least Bell's Vireo
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