Assessing Black-capped Vireo (Vireo atricapillus) Breeding Habitat based on Size, Spatial Distribution, and Plant Species in Shrub Mottes at Kerr Wildlife Management Area, Texas

Abstract

The Black-capped Vireo ( Vireo atricapillus) (hereafter, BCV), an endangered Neotropical, migrant songbird, inhabits semi-open areas ranging from a maturing scrubland to more open habitats. An important factor of BCV habitat is heterogeneity. BCVs inhabit areas with greater heterogeneity in vegetative cover. Vegetative cover in BCV habitat is composed of low deciduous shrubs with lateral branching to the ground. Openness, or distance between shrubs, is another important feature of heterogeneity as well as BCV habitat. The objective of my study was to determine suitable and unsuitable BCV habitat based on the size, spatial distribution, and plant species found in shrub mottes. The study took place at Kerr Wildlife Management Area (KWMA). Three pastures, Middle Trap, Plot 2 and Plot 3, were designated as unsuitable BCV habitat (LDBCV habitat) based on low BCV densities. North Rock, Fawn, and Doe were the three pastures designated as suitable habitat (HDBCV habitat) based on high BCV densities. I used the quadrat method to measure 5 response variables— canopy cover, distance between shrub mottes, number of shrub mottes, number of favorable mottes, and species richness. I examined differences between the LDBCV and HDBCV habitats using a multivariate analysis of variance (MANOVA). Five univariate ANOVAs were used to determine the extent of the main effects of the treatments on the response variables. Correlations using Pearson’s product moment correlations were made regarding canopy cover, distance between shrub mottes, and number of mottes. A t-test was used to examine differences between overall canopy cover per quadrats based on the mean canopy cover and number of mottes. During data collection, GPS locations of each shrub motte were recorded and downloaded into ArcGIS to emphasize the results of the statistics on maps. Suitable BCV habitat was considered heterogeneous and semiopen containing frequent mottes of various small sizes closely spaced with several plant species. Unsuitable BCV habitat was characterized as less heterogeneous and dense containing few, large mottes spaced far apart with few species.