Vireos prefer nesting in patchy or clumped, scrubby vegetation whose leaf cover extends to the ground. Warblers build nests in mature oak-juniper woodlands, stripping the juniper bark for building materials. Critical nesting habitat of the black-capped vireo, an endangered songbird, is found on Fort Hood. Unfortunately, both vireo and warbler populations have been in decline for decades. Black-capped vireos, which once ranged as far north as central Kansas during the breeding season, are mostly confined to central and western Texas and northern Mexico.
Warblers only breed in the fast-disappearing habitat of central Texas.
Brown-headed cowbirds are so named because of their association with cattle, which keep grasses cropped to lengths that make it easy for the birds to snatch insects. One of the cowbird's peculiarities is laying eggs in the nests of other birds. As a result, the nesting success of many species of songbirds has been reduced. The cowbird effect on other birds was localized so long as they were associated with wandering herds of bison. But now, cowbirds are adapted to livestock.