Abstracts

Presented by Alicia M. Berlin - Email: aberlin@usgs.gov

American black duck (Anas rubripes) utilize marshes throughout the Chesapeake Bay and are considered an indicator species of the ecosystems health. Thus, conserving and increasing black duck habitats will subsequently benefit the general health of the Bay. We used a bioenergetics model to determine the viable habitat types for wintering black ducks (where benefits outweigh costs during foraging) and modeled the influences of two stressors (sea-level rise and land use change) on these viable habitats. Captive black ducks exhibited a Type II functional response curves (intake rate exponentially increases with increases in prey density up to an asymptote) for R. maritima, Z. palustris, G. holbrooki, and M. bidentatus and a Type I functional response curve (linear relationship between intake rate and prey density) for S. validus. The critical foraging densities concluded in this study were 749 g/m2 for R. maritima, 435 g/m2 for Z. palustris, 26 g/m2 or 91fish/m2 for G. holbrooki, and 1.4 g/m2 or 24 snails/m2 for M. bidentatus. S. validus did not have a critical density as a result of having a linear relationship between intake rate and prey density. Quality habitat types for wintering black ducks when they arrive in the Fall were: 1. submerged aquatic vegetation (SAV), 2. high marsh; 3. low marsh, 4. mudflat, and 5. freshwater. Eastern shore refuges (Marshlands Refuge Complex) are at risk more from sea-level rise than development pressure, whereas, Western shore refuges (Virginia Rivers Refuge Complex) are at risk from both sea-level rise and development pressures. Ultimately the management and recovery of SAV in the Bay is potentially beneficial for wintering black ducks as long it does not become unavailable due to disturbance caused by close proximity to developed lands. Therefore, strategically placed SAV and living shoreline restoration efforts could provide more viable habitat for wintering black ducks.