The black-capped vireo requires a young, semi-open stand of small trees and shrubs, similar to the habitat seen at the Shin Oak Observation Deck.

During the winter, the black-capped vireo can be found on the west coast of Mexico, from southern Sonora to Guerrero. The male vireos leave the wintering grounds and arrive in Texas from late March to mid-April.

Males advertise their territories with song -– a varied bubbling series of notes punctuated with short pauses. The territories average 2-4 acres and males remain loyal to them throughout the breeding season, often returning to the same area in subsequent years. As soon as possible after she arrives, the female chooses a mate. The male will sometimes display to the female by swooping in an arc to a branch near the female. He also flutters his wings and displays his back, sometimes following her in flight, singing, and making chipping notes.

Nesting
Both sexes are involved in nest building. Nests are placed low in the vegetation, and can usually be found in various species of oaks. Dead oak leaves, cedar bark, and spider webs are the main materials found in the nests of this vireo. Once both adults are satisfied with their creation, the first egg is laid the next day.

The peak time for egg laying is June in Oklahoma and May in Texas. Both adults participate in incubating the eggs, but the female remains on the nest at night. They are very attentive during the day; one of the pair is always on the nest so that the nest is rarely left unguarded. Incubation lasts 13-17 days. The small white eggs hatch over a two-day period and the adults normally remove the eggshells from the vicinity.

Once the young are hatched, the male feeds them if the female is away from the nest when he arrives. If she is present, he gives her the food to give to the young birds. Newly fledged vireos remain near the nest, keeping in contact with the adults by calling and begging for food. In August and sometimes as late as September, the black-capped vireos leave for their wintering grounds in Mexico.

Threats to Survival
Habitat loss or alteration is the main reason why the black-capped vireo is endangered. They use the scrubby oaks and other low vegetation less than 15 feet high for nesting. These brushlands are often cleared to provide grazing for livestock. Under certain conditions, livestock can remove the low woody vegetation by intense grazing. Keeping the scrub vegetation in this stage can best be accomplished by a proper fire management program, which maintains the habitat preferred by these birds.

The presence of the parasitic brown-headed cowbird (Molothrus ater) is another major threat to the vireo. Cowbirds lay their eggs in the nests of vireos and other songbirds. The nesting bird does not recognize the difference between their eggs and cowbird eggs. Therefore, they incubate all the eggs in the nests. Cowbird eggs hatch earlier than vireos, and the young are larger than the vireo chicks. As a result, nests parasitized by cowbirds usually fledge only cowbird young.

Distribution
The historical breeding range of the black-capped vireo was south-central United States and north-central Mexico. They were once found as far north as central Kansas but because of the clearing of brushlands for agriculture and subsequent overgrazing by livestock, today, the black-capped vireo breeds only as far north as Blaine County, Oklahoma. There are two breeding populations in west-central Oklahoma as well one found in the Edwards Plateau of Texas.