|Listed||October 6, 1987|
|Description||Small olive-green songbird, with black cap and white "spectacles."|
|Habitat||Scattered trees and brush.|
|Reproduction||Clutch of three to five eggs.|
|Threats||Livestock grazing, cowbird brood parasitism.|
|Range||Kansas, Oklahoma, Texas; Mexico|
The Vireo atricapillus (black-capped vireo) is a small songbird, about 4.8 in (12 cm) long. Adult males are olive-green above and white below, with faintly yellow-green flanks. The crown and upper half of the head is glossy black with white "spectacles" around the eyes. It has brownish eyes and a black bill. Adult females are duller with a slate gray crown, and the underparts are washed with greenish yellow. Females and immatures resemble the solitary vireo.
Vireos are songbirds with a loud, emphatic warble. Cup-shaped nests are built in shrubs and small trees. Clutch size is from three to five tiny, white eggs. During the 14-17 day incubation period, the female incubates the eggs at night; males and females alternate during the day. Young fledge in 10-12 days, after which the female re-nests, occasionally with a different male. Black-capped vireos are shy and restless, flitting from twig to twig. Like other vireos, they are insectivorous.
The species is found in areas with scattered trees and brush. Many vireo territories are located on steep ravine slopes in rugged terrain where woody vegetation grows in clumps. Thick ground foliage is important for nesting. Most nests are found 1.3-4 ft (0.4 to 1.25 m) above ground, screened from view by foliage. Black-capped vireo habitat is naturally maintained by wildfires and grazing animals, which keep vegetation in an early successional stage.
The black-capped vireo formerly bred from Kansas through Oklahoma and Texas to central Coahuila, Mexico, with an outlying, possibly temporary, colony in Nuevo Leon, Mexico. Winter residents ranged from Sonora to Oaxaca, Mexico, but occurred mostly in Sinaloa and Nayarit. By 1954 black-capped vireos had disappeared from Kansas; the northernmost breeding range was northern Oklahoma. The present range is from Blaine County in central Oklahoma south through Dallas, the Edwards Plateau, Big Bend National Park, Texas, to Sierra Madera in central Coahuila, Mexico. A population count in 1986 found only 350 black-capped vireos: 44-51 adults at three sites in Oklahoma; slightly more than 280 adults at 33 sites in Texas; and 24 adults in Mexico. In 1990, searches of areas in Oklahoma where isolated groupings of vireos had been observed since 1985 located black-capped vireos (V. atricapillus ) in only two-the Salt Creek site in Blaine County and a site near Scott in Caddo County. Thirteen adult vireos were located, including six females. Five of the six females present in Blaine County produced 17 young. No females were seen at the Scott site. Three of six male vireos and one of three females banded in 1989 returned to the site in 1990.
The major threat to the black-capped vireo is loss of its nesting habitat. Suitable nesting areas have been altered by development, grazing by sheep and goats, and range improvements that remove broad-leaved, low, woody vegetation. The largest concentration of black-capped vireos is near Austin, Texas, in an area that is undergoing rapid development. Over 88% of the vireo population is immediately threatened by housing development and road construction. At the present rate, most of the bird's habitat will be lost within 10 years. Another important threat to the vireo is nest parasitism by brown-headed cowbirds. Deforestation and the expansion of cattle pasture over the past 150 years has favored the spread of the cowbird, which feeds near cattle. Cowbirds lay their eggs in vireo nests before the vireo clutch is complete. Cowbird eggs hatch two to four days before vireo eggs, and, by the time the vireos hatch, cowbird nestlings outweigh them tenfold. In all cases where a cowbird occupied the nest, no vireo chicks survived. When cowbird trapping was initiated in Texas and Oklahoma, nest parasitism dropped dramatically. The black-capped vireo is especially attractive to ornithologists and amateur birders. Unfortunately, nests have failed or been abandoned due to excessive attention from these admirers. Some egg and nestling predation by snakes and scrub jays also occurs.
Conservation and Recovery
Probable conservation activities still include cow-bird trapping in nesting areas and land management practices on government-owned land to maintain suitable habitat vegetation.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 25486
Denver Federal Center
Denver, Colorado 80225
Graber, J. W. 1961. "Distribution, Habitat Requirements, and Life History of the Black-Capped Vireo (Vireo atricapillus )." Ecological Monographs 31:313-336.
Grzybowski, J. A. 1985. "Final Report: Population and Nesting Ecology of the Black-Capped Vireo." U.S. Fish and Wildlife Service, Albuquerque.