Bell's Vireo

Measurements:

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)

In its breeding range, Bell's vireo often uses dense shrubbery in riparian areas or otherwise near water. Willow trees (Salix spp.) are a favored nesting species for all four subspecies of Bell's vireo, though in western areas mesquite and seep-willow (Baccharis salicifolia) are frequently used. Bell's vireos construct a hanging nest suspended between the ends of low tree branches. Bell's vireo nests are often parasitized by brown-headed cowbirds, reducing overall nest success; however, one California study found that vireo nests in upland habitat are parasitized less than those in river-adjacent riparian habitat.

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. …