Habitat Selection and Breeding Ecology of Bachman’s Sparrow (\u3ci\u3ePeucaea aestivalis\u3c/i\u3e) in a Wiregrass-Free Ecosystem

Through much of its range, Bachman’s Sparrow (Peucaea aestivalis) uses the wiregrass (Aristida spp.) dominant understory typical of longleaf pine (Pinus palustris) forest. The central South Carolina Coastal Plain, however, lies within the “wiregrass gap” where longleaf pine understories are absent of wiregrass and instead are dominated by bluestem grasses (Schizachyrium spp. and Andropogon spp.), bracken fern (Pteridium aquilinum), and shrubs. Habitat use of Bachman’s Sparrow in this region has yet to be studied and declining Bachman’s Sparrow populations necessitate a better understanding of habitat selection processes and population dynamics across regional habitat types. The goal of this study was to describe breeding season habitat selection and breeding ecology of Bachman’s Sparrow in the unique wiregrass-free longleaf pine ecosystem of Tom Yawkey Wildlife Center, Santee Coastal Reserve, and Washo Reserve, South Carolina to inform best management practices for Bachman’s Sparrow. I conducted repeated visit point count surveys at 95 sites and used open N-mixture models to estimate the effects of habitat management and forest stand characteristics (e.g. prescribed burns, basal area, stem density, pine species, canopy closure) on Bachman’s Sparrow abundance, apparent survival probability, and recruitment rates during the 2020 and 2021 breeding seasons. I also located nests to identify vegetation composition and structure characteristics that Bachman’s Sparrows select for nest-sites. To determine if habitat selection in the study population was adaptive, I monitored nests and related nest-site selection to nest survival rates by comparing habitat characteristics related to selection with those related to survival. Across the nine primary sampling periods, I estimated the abundance of male Bachman’s Sparrows within the study area to be between 23 and 49 individuals. Initial abundance and recruitment rate were strongly predicted by the proportion of longleaf pine to other pine species within the sample area, with abundance and recruitment rate increasing with longleaf pine dominance. Apparent survival probability decreased as the density of stems between 10 and 25 cm DBH increased. Nest-site selection in the study population was non-adaptive. Bachman’s Sparrows selected nest-sites that had intermediate groundcover densities compared to available nest-sites; however, nest survival rates decreased at intermediate groundcover densities. The results of this study can be used to inform region-specific management plans and restoration of degraded habitats, which often lack typical understory species like wiregrass, to increase Bachman’s Sparrow abundance and reproductive success