Nest Height and Vertical Vegetation Associated with Black-capped Vireo Breeding Success in Southwest Texas

Authors: Kathryn N. Smith-Hicks, Tara J. Conkling, Michael L. Morrison, James W. Cain III, R. Neal Wilkins

Vireo atricapilla (Black-capped Vireo) is an endangered songbird whose habitat use has been well studied in central portions of its breeding range, which is characterized by successional vegetation communities. To expand our understanding of habitat use as it relates to reproductive success, we studied Black-capped Vireo habitat use at the territory and nest-site scales in southwest Texas in 2009 and 2010, an area characterized by xeric and stable vegetation communities. We measured vegetation in territories and at nests to evaluate the influence of habitat variables on nest parasitism and nest survival.

Our results showed that Black-capped Vireo nest-site use in southwest Texas differed from that in breeding areas of central Texas and Oklahoma. Black-capped Vireos in southwest Texas used nest sites with a wide range of woody cover (70 ± 13%) and used Juniperus spp. (junipers) as a nest substrate proportionately more than its availability in territories, which is contradictory to previously published literature. Nest parasitism increased significantly with greater nest height, likely due to increased visibility to Molothrus ater (Brown-headed Cowbird). Increasing height of vertical cover above the nest was associated with decreased overall nest survival, likely because nests placed in habitat with taller vegetation are more susceptible to avian predators and Brown-headed Cowbird parasitism.

Unlike the findings of studies conducted in the northern part of the species' breeding range, we found that parasitism did not increase the likelihood of depredation or abandonment. Our results indicate that Black-capped Vireo habitat structure and composition, as well as factors influencing nest success in Southwest Texas, differ from their breeding habitat in central Texas and Oklahoma, indicating that management guidelines need to be regi on-specific.