Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Wildlife and Fisheries Resources
Petra B. Wood
James T. Anderson
George T. Merovich
Shrubland songbirds are a highly imperiled guild across much of North America due to wide-scale land use changes and resulting loss of shrubland habitat. Land management practices which produce early-successional habitat, namely field abandonment and clearcut timber harvests, have become increasingly uncommon in the eastern United States, and natural maintenance processes such as fires and floods are often suppressed. The Appalachian region is rich in natural resources; it has historically seen high amounts of surface mining for coal and is currently experiencing prolific development of shale gas. Both of these practices alter local habitats and the landscape, and it is essential to understand their impacts on shrubland songbirds in order to inform conservation efforts for this declining guild. Research for this thesis was composed of three studies during the breeding seasons of 2012-2013 on four shrubland sites in southwestern Pennsylvania and the northern panhandle of West Virginia. This work aimed to fill knowledge gaps in shrubland songbird ecology and responses to extractive land uses. In my second chapter I focus on habitat selection patterns and nesting ecology of one species, the Blue-winged Warbler (Vermivora cyanoptera). This species has not been studied much outside of its antagonistic relationship to the closely related and highly imperiled Golden-winged Warbler (Vermivora chrysoptera). A quantitative habitat selection study for the species has never been done, although knowing habitat requirements is key to effective conservation measures. I found significant differences in vegetative structure between territories and random plots using non-parametric MANOVA, indicating strong patterns of territory selection. Blue-winged Warblers placed territories in later stages of succession relative to the sites as a whole, having more woody structure, taller vegetation, more shrub, sapling, and canopy cover, and were closer to forest edge than random points. My third chapter is a study on the impact of unconventional shale gas development on shrubland songbird nest success, abundance, and community composition. The practice of unconventional gas development is new to the eastern United States and has become controversial due to concern over environmental impacts, but few studies have been done on the potential effects to terrestrial biota, especially in the east. My objective was to fill a specific research gap, the impacts of development on shrubland songbirds in an already-fragmented landscape context, because this is where both shale gas development and shrubland songbirds are more likely to occur. During the 2013 breeding season, I determined the effects of gas development presence at different spatial scales on shrubland songbird nest success and community dynamics and quantified noise and light emissions from developed pads. There were no differences in noise or light emissions between impacted and non-impacted shrublands, or at a developed site with increasing distance from the wellpad. The presence of gas wells and related infrastructure were important influences on Field Sparrow (Spizella pusilla) nest success; survival was reduced close to the wellpad and increased near pipelines and roads. However, nest survival was higher site-wide for the Field Sparrow and other early successional species on the impacted site than on non-impacted shrublands in the region. Nest predators were important in explaining nest survival variation at the site-level. Within the developed site, nest abandonment was a more likely force near wells and a paved road, while predation better explained variation in survival by distance to the pipeline and unpaved access road. Avian communities significantly differed between impacted and non-impacted sites but the differences were not extractable from vegetative differences. Shannon's diversity and species richness did not differ between impacted and non-impacted sites and had no significant trend with increasing distance from the developed well. Although unconventional gas extraction is new to the region, surface mining has historically been a common practice in Appalachia. Once mining has ceased, these areas stay in early succession conditions for extended durations due to poor topsoil quality, providing habitat for early-successional species which endures on the landscape much longer than habitats in abandoned fields or recent clearcuts. Reclamation of surface mines to a vegetated state is mandated by federal law, but questions have been raised on the habitat quality of the resulting areas. Many studies have assessed the use of former surface mines by various species and the success of grassland-nesting songbirds in these habitats, but none have quantitatively compared nest survival and avian community composition between former surface mines and non-mined shrublands. In my fourth chapter, I determined the utility of former surface mines as breeding habitat for shrubland songbirds. I performed site-level comparisons of community composition, species abundances, and nest survival of three focal species to determine if these metrics differed between former surface mines and non-mined shrublands and also between a reclaimed and a non-reclaimed former surface mine. Whether a site was mined or not was an important factor influencing nest success, as was whether a mined site was reclaimed or not. Daily survival rates of nests for all three species were higher on mined sites and higher on the reclaimed former surface mine. Avian communities did not differ between mined and non-mined sites. Community composition on the reclaimed and non-reclaimed former surface mine sites differed, but most species were detected on both. Vegetative conditions on mined sites were broader and encompassed the range of structure at non-mined sites, providing similar habitat for species found at unmined shrublands, plus more. All sites significantly differed in vegetative characteristics. Higher nest survival on mined sites may result from the higher vegetative heterogeneity there. The reclaimed site may have had higher nest survival due to lower rodent and corvid nest predator abundances. This research informs conservation efforts of the declining early-successional songbird guild and answers questions about the impacts of common energy extraction practices on these species. Blue-winged Warblers select conditions of later succession for nesting, which demonstrates that the early-successional sere should not be treated as a homogeneous management unit which spans only a few years after disturbance, but maintained over a range of ages on the landscape. Unconventional gas development in an already-fragmented landscape context may not degrade shrubland songbird habitat as much as it does interior forests, but does impact nest success and results in the displacement of large amounts of habitat. Former surface mines provide productive, lasting habitats for breeding shrubland songbirds that accommodate the early-successional songbird guild comparably to unmined shrublands. Shrubland songbirds can coexist with the ever-expanding extraction of fossil fuels from Appalachia if their habitat requirements are met. These species rely upon ephemeral conditions, and the key to retaining them remains management of the landscape in a dynamic fashion to provide ample habitat.
Davis, Ryan Douglas, "Impacts of non-renewable resource extraction on shrubland songbird nest success and abundance" (2014). Graduate Theses, Dissertations, and Problem Reports. 296.