REGIONAL-ANALYSIS OF BLACK-CAPPED VIREO BREEDING HABITATS

Structural vegetation components of Black-capped Vireo (Vireo atricapi llus) breeding habitats and unoccupied scrubland areas were analyzed a t 13 sites from three regions: the Lampasas Cut Plains in central Texa s; the Wichita Mountains and adjacent areas in western Oklahoma; and t he Edwards Plateau (Kerr County) in central Texas. We evaluated 61 veg etation variables from individual vireo territories and equivalent scr ubland plots unoccupied by vireos. Principal components indicated stro ng vegetation trends for all plots involving the abundance of junipers (from high to low) and openness (from low to high) extending from the Lampasas Cut Plains to the Wichita Mountains and then to the Edwards Plateau. In all regions, vireo territories had relatively high densiti es of deciduous vegetation (primarily oaks) close to the ground (i.e., up to 1-2 m, and in one region 3 m). In addition, vireo territories o ccurred where variation in relative density measures of woody vegetati on was highest. However, even with the vireo's limited geographic rang e, differences were found among regions in the vegetational characteri stics of areas defended by territorial males. Vireos avoided higher ju niper densities on the Lampasas Cut Plains and more open areas on the Edwards Plateau. On the Edwards Plateau, with generally less dense veg etation and the lowest density of junipers, the older (ASY; after-seco nd-year) males selected territories with higher juniper densities at l ower height intervals than found on nonvireo plots. Territories of sec ond-year males (SY) and older males (ASY) differed in vegetation chara cteristics. On the Edwards Plateau, SY males occupied territories with vegetation structurally more like nonvireo plots than like territorie s of ASY males. In the Wichita Mountains, where a remnant vireo popula tion occurs, territories of SY males were similar to those of ASY male s. In both regions, however, SY males were found in more open habitats . Competition with other foliage-gleaning species may have played a ro le in restricting the Black-capped Vireo to early successional stages of scrubland habitats, where they also may effectively avoid several s pecies of nest predators. Periodic habitat disturbance has beneficial effects for vireos and can be used in management of this endangered sp ecies. Attempts should be made to maintain 35 to 55% dispersed scrub c over (primarily deciduous) in spatially heterogeneous configurations. Sometimes inherent site characteristics (e.g., poor soils) may natural ly promote the degree of vegetational heterogeneity requisite for Blac k-capped Vireos. Managers should employ techniques that encourage thic k regrowth of deciduous woody vegetation. Typically, juniper cover sho uld be kept well below 10%, which may be possible only through habitat manipulation. However, in areas where amounts of deciduous vegetation are marginal (e.g., Edwards Plateau region and to the southwest), jun ipers may contribute important cover. Thus, site and regional characte ristics need consideration when making decisions about juniper control .