Family: Vireonidae, Vireos view all from this family
Description 4 3/4 -5" (12-13 cm). Smaller than a sparrow. Dull olive-gray above, whitish below, with faint white eye ring and fainter wing bars. White-eyed Vireo similar but larger, with yellow "spectacles" and white eyes.
Endangered Status The Least Bell's Vireo, a subspecies of Bell's Vireo, is on the U.S. Endangered Species List. It is classified as endangered in California. This little vireo lives in dense, streamside willow thickets from southern California into Baja California. The alteration of its habitat, caused mainly by water diversion practices, was a major factor in this vireo's decline. The stresses of habitat loss made the bird vulnerable to other factors. One of these is nest parasitism by cowbirds, which lay their eggs in the vireos' nests. The cowbird young crowd and starve out their hosts smaller offspring. There are thought to be about 300 breeding pairs of Least Bell's Vireos surviving.
Habitat Dense bottomland thickets, willow scrub, and mesquite.
Nesting 3-5 white eggs, sparsely marked with brown, in a well-made pendant cup of plant down and bark strips, placed in a dense tree or shrub.
Range Breeds from southern California, Colorado, Dakotas, and Indiana southward. Absent from eastern third of United States. Winters in tropics.
Voice Fast, warbled tweedle-deedle-dum? tweedle-deedle-dee! First phrase up, second phrase down.
Discussion The species was named by Audubon for John G. Bell (1812-1899), a New York taxidermist who accompanied him on his trip up the Missouri River in the 1840s. Incubating Bell's Vireos, like other vireos, are so fearless around their well-camouflaged nests that an observer may photograph them from a few feet away. The strong, somewhat curved beak, with a slight hook at the end, like a miniature of a shrike's beak, reminds us that these birds, however gentle they seem, are determined predators. They feed on caterpillars, aphids, various larvae, and spiders. Although often victimized by cowbirds, this bird raises relatively few of the brood parasites, simply abandoning a nest when a cowbird's egg is laid in it.
