Shrub cover and height determine the density of <i>Vireo atricapilla</i> (Black-capped Vireo) at two national wildlife refuges

ABSTRACT Determining habitat associations for shrubland bird species can be challenging because of the structural and compositional complexity of shrubland plant communities. Remote-sensing products, such as laser altimetry from airborne light detection and ranging (LiDAR) and multispectral imagery, are becoming increasingly important tools for describing habitat features in wildlife studies as these tools allow for rapid and multidimensional characterization of vegetation characteristics that can shape a species density across the landscape. In this study, we assessed the influence of vegetation variables derived from LiDAR and high-resolution multispectral and multitemporal imagery on the densities of Vireo atricapilla (Black-capped Vireo), a shrubland obligate species and a species of conservation concern in the southern Great Plains, on 2 national wildlife refuges located in Oklahoma and Texas, USA. Using point-count data collected during 2015–2016 at both refuges, we used hierarchical distance sampling and information-theoretic methods to compare a suite of variables that describe shrubland composition, vegetation height, and spatial arrangement of shrubs to determine which factors most strongly influenced V. atricapilla density across both refuges. Vireo atricapilla densities were highest in areas with 50–70% coverage of broadleaf shrubs. Vireo atricapilla densities were also negatively related to the average canopy height of shrubs and trees, with densities rapidly declining once the average canopy height exceeded 2 m. Variables describing the spatial arrangement of shrubs were generally not supported. Based on these results, management strategies that promote intermediate coverage of shrubs while limiting the growth of tall trees will be critical for maintaining V. atricapilla habitat. This work also demonstrates the value of remote-sensing tools to describe shrubland structure when investigating habitat associations of species of conservation concern.