AN ABSTRACT OF THE THESIS OF Benjamin S. Lewis Jr., for the Master of Science degree in ZOOLOGY, presented on December, 2, 2015 at Southern Illinois University Carbondale. TITLE: DETERMINING FOOD RESOURCES FOR AMERICAN BLACK DUCKS WINTERING AND SPRING STAGING ON THE EASTERN SHORE OF VIRGINIA MAJOR PROFESSOR: Dr. Michael W. Eichholz I evaluated food availability and food preference for American black ducks (Anas rubripes) wintering and spring staging on the Eastern Shore of Virginia during 2006–2007 and 2007–2008. I estimated food availability by taking core and sweep net sample at 78 sites selected by a stratified random sample throughout our study area, representing 4 dominant wetland habitat types. Seed and invertebrate biomass found in each of these samples were converted to measurements of kilograms per hectare. I found that salt marsh and mudflat habitats contained the highest amount of invertebrate biomass, while freshwater habitats contained the highest amount of seed biomass. I estimated food preference by collecting crop samples from 76 foraging black ducks. Animal matter made up 73% of the aggregate percent biomass of all foods eaten by black ducks. Foods found in black duck crops were compared to their availability in the environment and classified as either selected for, avoided or consumed relative to their availability. Although they were not found to be the most abundant foods, amphipods (Gammarus spp), salt marsh snails (Melampus bidentatus) and ribbed mussels (Geukensia demissa) were foods selected for in black duck wintering habitats. These food items are found most predominantly in salt marsh and mudflat habitats. As may be expected these areas are identified as the most important habitats for black ducks wintering on the Eastern Shore of Virginia. Results from this study provide energetic supply data for bioenergetically based habitat conservation for black ducks in Virginia and in the Atlantic Flyway. I found that the density of food items available for wintering black ducks were lower than densities found in in the more northern wintering range of the black duck and considerably lower than estimates from the wintering regions of other species of dabbling ducks. By concurrently measuring food selection and availability I was also able to reliably determine food preference. Removing avoided food items from food availability estimates provides more accurate estimates of preferred food biomass and it is important for bioenergetically based habitat models to use estimates of preferred food biomass in determining habitat objectives. I found that when avoided food items are removed, estimates of available food biomass decrease substantially, (up to 97%) further emphasizing discrepancies in estimates of food availability between coastal black duck wintering areas and estimates from the wintering regions of other species of dabbling ducks.

Several factors have contributed to impeding the progress of migratory waterfowl spatial modeling, such as (1) waterfowl’s reliance on wetlands, (2) lack of understanding about shifts in distributions through time, and (3) large-scale seasonal migration. This doctoral dissertation provides an array of tools to address each of these concerns in order to better understand and conserve this group of species. The second chapter of this dissertation addresses issues of modeling species dependent on wetlands, a dynamic and often ephemeral habitat type. Correlation models of the relationships between climatic variables and species occurrence will not capture the full habitat constraints of waterfowl. This study introduces a novel data source that explicitly models the depth to water table, which is a simulated long-term measure of the point where climate and geological/topographic water fluxes balance. The inclusion of the depth to water table data contributes significantly to the ability to predict species probability of occurrence. Furthermore, this data source provides advantages over traditional proxies for wetland habitat, because it is not a static measure of wetland location, and is not biased by sampling method. Utilizing the long-term banding bird data again, the third chapter examines the behavior of waterfowl niche selection through time. By using the methods developed in chapter two, probability of occurrence models for the 1950s and the 1990s were developed. It was then possible to detect movements in geographic and environmental space, and how movements in these two spaces are related. This type of analysis provides insight into how different bird species might respond to environment changes and potentially improve climate change forecasts. The final chapter presents a new method for predicting the migratory movement of waterfowl. The method incorporates not only the environmental constraints of stopover habitat, but also includes likely distance and bearing traveled from a source point. This approach uses the USGS’ banding bird database; more specifically, it relies on banding locations, which have multiple recoveries within short time periods. Models made from these banding locations create a framework of migration movement, and allow for predictions to be made from locations where no banding/recovery data are available. / text