Thesis (Ph.D.) - Indiana University, Environmental Science, 2009Plant, invertebrate and feather δ13C and δ15N stable isotopic signatures were used to trace avian plant production sources and prey items in five habitats of coastal Georgia: tidal forest, oak forest, pine forest, shrub and saltmarsh. Isosource 1.3.1 mixing models of plant production sources were successful on Sapelo Island where there were large differences in photosynthetic pathways and hydrology, but failed in the Clayhole Swamp. Model sensitivity analysis indicated that the trophic position was the most important parameter to know for partitioning plant production sources and isotopic enrichment of δ13C and δ15N in birds were equally important in determining prey items. Painted Buntings, the species of highest concern in the region, were almost as dependent on saltmarsh vegetation as they were on shrub and forest vegetation (~40%). Greater dependence of young of year Yellow-throated Warblers, White-eyed Vireos and Brown-headed Nuthatches on C3 saltmarsh vegetation suggests the saltmarsh may be providing an important source of protein for nestling birds across all habitats on Sapelo Island. Avian conservation efforts in coastal Georgia should include nearby saltmarsh to provide not only the necessary food resources for shrub-associated species, but also for forest interior species during the breeding season. Estimated habitat changes for 2100 due to climate change induced sea-level rise and coastal development indicate that sea-level rise is the greatest threat to saltmarsh and coastal shrub habitat, whereas accelerated urban development is the greatest threat to oak and pine forests. Tidal forests may serve as important refuges for closed-canopy species, such as Northern Parula, that will lose their preferred oak and pine habitats.