Winter waterbird and food dynamics in autumn-managed moist-soil wetlands in the Mississippi Alluvial Valley

Managed moist-soil wetlands are important habitats for waterfowl and other waterbirds in the Mississippi Alluvial Valley (MAV) and elsewhere in North America. These wetlands often contain abundant food resources, but they also contain tall and dense (i.e., robust) vegetation that may constrain use and foraging by waterbirds. During winters 2006-2009, we estimated densities of waterbirds, seeds and tubers, and aquatic invertebrates following autumn, preflooding treatments of disking, mowing, and no manipulation (control) of robust vegetation in 26 moist-soil wetlands in and near the MAV. In late autumn, seed and tuber dry mass was greater in control (x̄ = 750.7 kg/ha) and mowed (x̄ = 709.7 kg/ha) than disked plots (x̄ = 509.8 kg/ha). Dabbling ducks (Anatini) accounted for 92% of all waterbirds observed and were 2-3 times more abundant in mowed and disked than control plots during winter. Invertebrates comprised <1% (dry mass) of potential waterbird foods, but were greatest in control plots throughout winter. In mid- and late winter, residual seed and tuber masses were similar among mowed, disked, and control plots within study sites (approx. 260 kg/ha), despite different waterbird use. We recommend 1) active management of moistsoil wetlands, including partial autumn mowing of robust vegetation to increase use by waterbirds; 2) that conservation planners consider increasing foraging thresholds (e.g., giving-up density) in carrying-capacity models for moist-soil wetlands; and 3) additional experiments to describe foraging thresholds in moist-soil and other wetlands targeted by the North American Waterfowl Management Plan.