Abstracts

Presented by Margaret Gross - Email: margaret.gross@state.mn.us

Improving the accuracy of energetic models used to set and evaluate habitat objectives to meet dietary needs of waterfowl requires true metabolizable energy (TME) estimates for numerous diet items. While significant effort has been devoted to estimating TME of moist-soil seeds, hard mast, agricultural grains, and invertebrates, few TME values exist for submersed aquatic vegetation, despite its significance in the diets of many waterfowl species. We conducted 340 TME assays and estimated TME for 21 vegetation and duck species combinations using the foliage of eight submersed aquatic vegetation species (southern naiad [Najas guadalupensis], Canada waterweed [Elodea canadensis], coontail [Ceratophyllum demersum], wild celery [Vallisneria americana], sago pondweed [Stuckenia pectinata], widgeongrass [Ruppia maritima], hydrilla [Hydrilla verticillata] and Eurasian watermilfoil [Myriophyllum spicatum]) with four duck species (mallard [Anas platyrhynchos], ring-necked duck [Aythya collaris], wood duck [Aix sponsa], and gadwall [Mareca strepera]). True metabolizable energy among combinations ranged from 1.07 (sago pondweed foliage, gadwall) to 1.92 kcal/g (hydrilla foliage, ring-necked) with an overall mean of 0.63 0.18 kcal/g. Among duck species, TME was greatest for hydrilla (x = 1.56 kcal/g) followed by Canada waterweed (x = 1.18 kcal/g), coontail (x = 1.01 kcal/g), widgeongrass (x = 0.78 kcal/g), Eurasian watermilfoil (x = 0.41 kcal/g), southern naiad (x = 0.38 kcal/g), sago pondweed (x = 0.02 kcal/g), and wild celery (x = 0.08 kcal/g). Generally, mean TME for most submersed aquatic vegetation species was less than agricultural grains, but it was similar to ranges reported for moist-soil seeds and other natural wetland vegetation and aquatic macroinvertebrates. We recommend that conservation planners incorporate our TME estimates into energetic models used in wetland restoration and protection objectives because submersed aquatic vegetation provides significant energy for waterfowl.