Bird Story: Black-Capped VireoHope for Survival?
for National Geographic BirdWatcher
|January 31, 2003|
The black-capped vireo is a little bird with a big problem. Its population and breeding range have decreased so much that it was placed on the endangered species list in 1987. Without help, black-capped vireos seemed unlikely to survive in the United States.
Up through the early part of the 20th century, black-capped vireos spent every season but winter in Kansas, Oklahoma, and Texas. In August and September they migrated to the West Coast of Mexico. By about 1930, they had disappeared from Kansas. Today they are only found in west-central Oklahoma and in a region of Texas that includes the Edwards Plateau, Cross Timbers and Prairies, Trans-Pecos, and the Chisos Mountains.
To breed and nest, black-capped vireos require a habitat of a mixture of scrubby deciduous growth with vegetation close to the ground, tall trees, and some open ground. But the habitat is diminishing. In breeding areas, vegetation used to be kept in a state of succession by wildfire. Under such wild conditions, dense tiers of successional deciduous vegetation and cover often extended from the ground to about six to ten feet, providing favorable nesting cover for the birds. But recent government policy has been to control fire, resulting in more older growth, which is unsuitable for these birds. Along with human settlement and ranching came land management for cattle and urban sprawl. According to one assessment, housing and road construction threatens nearly 90 percent of the vireo population in the U.S. Even when roads merely pass through vireo habitat, they cause problems because they create more "edges," a favorite domain of the brown-headed cowbird, which for the vireo is the second greatest problem after loss of habitat. The cowbird is a parasite whose reproductive strategy involves depositing its eggs in the nests of other birds, who then hatch the alien eggs and feed the cowbird hatchlings. Studies have revealed that as many as 90 percent of the vireo nests in Texas and Oklahoma have been invaded by cowbirds. Under such predation, black-capped vireos fail to reproduce at a rate that can sustain their population.
Reasons for Hope
Controlling the population of cowbirds is critical in this struggle. After a cowbird trapping program had been implemented at Fort Hood, Texas, and on nearby ranches, the vireos' low 5 percent reproductive success rate of 1987 leaped to 45.5 percent in 1996. Trapping is an expensive, short-term solution, though, that mostly helps local populations. Programs undertaken by the state and federal government and civic organizations are improving the vireos' odds. In 1992 Balcones Canyonlands National Wildlife Refuge was established near Austin, created principally for conservation of endangered species, including the golden-cheeked warbler and the black-capped vireo. As of October 2002, however, only 18,000 acres of the proposed 46,000 acres had been acquired. The federal government has entered into safe harbor agreements with landowners to encourage them to restore habitat for endangered species.
The U.S. Army is also involved in studying the birds at Fort Hood. More than 25 percent (66,000 acres) of the fort's area is managed for preservation. Because of efforts among such diverse groups, there is reason to hope that the black-capped vireo will survive.
Howard Robinson is a member of the National Geographic BirdWatcher staff.
Where and when to look for black-capped vireos
Texas: Black Gap Wildlife Management Area, Colorado Bend State Park (SP), Devils River State Natural Area, Dinosaur Valley SP, Kerr Wildlife Management Area, Kickapoo Caverns SP, Lost Maples State Natural Area, South Llano River SP, Balcones Canyonlands NWR, Government Canyon SP (near San Antonio), and Buck Wildlife Management AreaThe Shin Oak Observation Deck at Balcones opens in late April.
Oklahoma: Wichita Mountains NWRbetween mid-May and early July. Finding black-capped vireos is not a sure thing, partly because only a limited number of birds nest in the public use areas.
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