Black Capped Vireo (Vireo atricapilla)
(Federally listed as Endangered)
Description: This is a small songbird approximately five inches in length. The back, wings and sides are a greenish color, and the head is either black (in males) or gray (in females). The breast and belly are white, and there are white markings around the eyes and above the bill that look like spectacles. Black-capped Vireos feed primarily on soft-bodied insects, especially caterpillars, that they glean off of leaves and twigs.
Habitat: Black-capped Vireos are typically found in low brushy thickets comprised of deciduous trees such as oaks, redbuds and plums. These thickets are often found on thin and rocky soils that slow or stunt the growth of trees and maintain the low thickets that the vireo prefers. Periodic fires and drought are important in maintaining this scrubby habitat. Black-capped Vireos are migratory and occur in Oklahoma between mid-April and early September. Vireos form breeding pairs shortly after returning to Oklahoma and their nesting season begins in the first week of May and continues through mid July. Vireos lay their eggs in small hanging nests that are normally constructed at the end of a branch and commonly hidden by overhanging leaves. Nests are usually built only four to eight feet above the ground, and vireos lay an average of four eggs. Most pairs of vireos raise one brood of chicks per year, although a small percentage may rear two broods.
Current and Historic Distribution: Currently, there are only two known populations of Black-capped Vireos in Oklahoma. One population is large (over 2,000 birds) and is located in the Wichita Mountains of northern Comanche County. The other population is small (less than 30 birds) and is located in the canyon lands of northern Blaine County north of Watonga. Historically this species was once more widespread in central Oklahoma and was found in scattered locations in the Cross Timbers region of the state. Nesting populations also remain in portions of northern Mexico and central Texas including the Edward’s Plateau. During the fall, all Black-capped Vireos in Oklahoma and Texas migrate south to spend the winter in southern and western Mexico.
Reasons for Decline: Vireo populations have declined for several reasons including the loss and modification of their nesting habitat. Much of their oak scrub habitat has been cleared and converted to cropland or non-native pastureland. The condition of most of their remaining habitat has declined as a result of fire suppression which has allowed the encroachment of taller vegetation such as Eastern Redcedar. Nest parasitism by the Brown-headed Cowbird is another contributing factor. The Brown-headed Cowbird lays its eggs in the nests of songbirds such as vireos, and in the case of the Black-capped Vireo the young cowbirds hatch sooner and are larger than the young vireos so they typically cause the deaths of all of the vireo chicks in the nest. Brown-headed Cowbird populations have increased over the past century as a result of changes in the populations of large grazing animals in the U.S.