Black-capped vireo  (Vireo atricapilla)

The black-capped vireo is classified as Vulnerable (VU) on the IUCN Red List (1).

The black-capped vireo (Vireo atricapilla) is a small, beautifully-marked songbird. The male black-capped vireo is olive green with a bright white chest and belly. Intermittent yellow feathers provide flashes of colour on the wings, tail and flanks. The top of the head is black and a distinctive white ring encircles each eye. The female black-capped vireo has slightly duller plumage than the male, with a greenish-yellow chest and belly, and a slate grey crown. Both sexes have brownish-red eyes (3).

The song of the black-capped vireo is a harsh and hurried tune of two to three note phrases (4) (5), and its call is a dry ‘chit-it’ (5).

A migratory species, the black-capped vireo breeds in Texas and Oklahoma in the United States, and the state of Coahuila in northern Mexico before migrating south to spend winter along the western coast of Mexico (4).

The black-capped vireo inhabits areas of low dense, shrubby, deciduous growth in fire maintained scrubland and forest-grassland ecotone (a zone of transition between two different ecosystems) (5).

The black-capped vireo feeds primarily on insects, particularly the adults and larvae of moths, butterflies and beetles which are plucked from plant surfaces as it hops and flutters amongst thick vegetation. It supplements this diet with seeds, particularly during the winter (6) (7).

The breeding season of the black-capped vireo takes place from March to July (6) (7). The male establishes a territory of between two and four acres, shortly after which the females arrive and select a male based on the quality of their territory (7). During this time, the male deters rivals with songs, displays and fights (6) (7).

Once a breeding pair has formed, the black-capped vireo builds a cup-shaped nest that is suspended from the fork of a branch, up to two metres off the ground (4). This impressive structure takes two to three days to complete (4). A day after completion of the nest, the female lays the first egg, and will lay a further egg each subsequent day (4), until three or four eggs have been laid (6). Both adults incubate the eggs for 14 to 17 days (4) and share the task of feeding the new chicks (6), until they leave the nest 10 to 12 days after hatching (4). The black-capped vireo has an average lifespan of five to six years (6).

Fire suppression strategies are considered one of the most serious threats to the black-capped vireo (5). Natural, periodic fires maintain a suitable habitat of open grassland with scattered clumps of trees and shrubs for the black-capped vireo. A lack of fire in many areas, as a result of suppression strategies by humans, has reduced the amount of suitable habitat (4).

Urban development, the conversion of land for agriculture, and intensive grazing have also caused significant habitat loss (4) (5).

Unfortunately, these human-caused changes to the habitat has created more favourable conditions for the brown-headed cowbird (Molothrus ater), a brood parasite of black-capped vireo nests. The brown-headed cowbird lays its eggs in other birds’ nests, leaving the host parents to care for the eggs and chicks (4). The cowbird egg typically hatches before the black-capped vireo eggs, and so once the vireos hatch, they are rarely able to compete with the larger cowbird chick for the host parent’s food. As a result, young vireos seldom survive when cowbirds share their nest (8).

The Balcones Canyonlands National Wildlife Refuge in Texas protects a key population of black-capped vireos and is the site of a cowbird trapping programme which has successfully reduced brood parasitism (5). These measures have also been implemented at other sites in Texas, such as Fort Hood, and in the Wichita Mountainsin Oklahoma (5). In addition, the Leon River Restoration Project in Texas is working to restore suitable habitat for the black-capped vireo and another endangered species, the golden-cheeked warbler (Dendroica chrysoparia) (5).

View information on this species at the UNEP World Conservation Monitoring Centre.

Learn more about the black-capped vireo:

• National Audubon Society – Black-capped vireo:
  http://web1.audubon.org/science/species/watchlist/profile.php?speciesCode=blavir1
• BirdLife International – Black-capped vireo:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=5563