Vulnerability Assessment of Available Habitat for Wintering Black Ducks within the Refuge System in the Chesapeake Bay

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American black duck (Anas rubripes) utilize inland and tidal freshwater and brackish marshes throughout the Chesapeake Bay and are considered to be an indicator species of the ecosystem’s health. Thus, conserving and increasing black duck habitats will subsequently benefit the general health of the bay. The goal of this study was to create a mechanistic model to determine the amount of energetically viable habitat available for wintering black ducks within the refuges of the Bay including a 5 km buffer of surrounding habitat and produce management recommendations for increasing the quality and quantity of habitat available in the face of sea-level rise and development projections.

The Challenge: Executive order 13508 Chesapeake Bay Strategy requires a three-year average wintering black duck populations in the Chesapeake Bay watershed of 100,000 birds by 2025. Recent average at 37,158 black ducks in the Chesapeake Bay. By 2017, National Wildlife Refuges will increase by 10 percent the availability of food resources to support energetic carrying capacity for wintering black ducks on refuge lands located within the Chesapeake watershed. The increase of food resources on refuges will be accomplished through active wetland restoration and management, habitat protection, invasive species control and potential expansion of refuges.

The Science: USGS scientists designed and used a bioenergetics model to determine the viable habitat types (where benefits outweigh costs during foraging). These five key habitat types for wintering black ducks were mapped using Wetlands Inventory, mean tide, and vegetation survey data for each refuge (with a 5km buffer) within the Bay.  Scientists then modeled the influences of two stressors (sea-level rise and land use change) on these viable habitats.

The Future: This project noted that 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. In addition, 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. Further research is needed on how the bioenergetics modeling could be adjusted to account for competition between individuals or other species. Also future projections of SAV are needed to better understand potential changes in carrying capacity for black ducks given that SAV was found to be the optimal habitat for wintering black ducks.