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Wednesday, January 31 • 8:20am - 8:40am
WATERFOWL: True Metabolizable Energy of Submersed Aquatic Vegetation for Ducks

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AUTHORS. Margaret Gross, INHS Forbes Biological Station - Western Illinois University; Christopher Jacques, Western Illinois University; Heath Hagy, U.S. Fish & Wildlife Service; Sarah McClain, INHS - Forbes Biological Station; Aaron Yetter, INHS - Forbes Biological Station

ABSTRACT. Wetland vegetation communities provide critical foraging habitat for waterfowl and are disappearing at an alarming rate.There is a lack of information regarding how the energetic carrying capacity for waterfowl is affected in degrading wetland ecosystems where submersed aquatic vegetation (SAV) is present. Managers can estimate the energetic carrying capacity for a wetland by determining the energetic value (true metabolizable energy; TME) of foods available to ducks. Although energetic carrying capacity models are sensitive to TMEs, few TMEs are available for SAV. Most available TME values are from plant seeds and have only been estimated from waterfowl that do not primarily consume SAV. We estimated TME values of eight common species of SAV for mallards (Anas platyrhynchos), gadwall (Mareca strepera), and ring-necked ducks (Aythya collaris) to parameterize energetic carrying capacity models. We used established TME methods which consisted of fasting and feeding ducks a known amount of vegetation, and subsequently collecting their excreta.  Excreta was dried, ground, pressed into pellets, and combusted in a Parr 6050 compensated jacket calorimeter to determine gross energy. We calculated TME from gross energy of raw vegetation and excreta. Preliminary results for mallards indicate that TME was greatest for Canadian waterweed (Elodea canadensis; 1.69 ± 0.33 kcal/g) and southern naiad (Najas guadalupensis; 1.40 ± 0.43 kcal/g) and lowest for Eurasian watermilfoil (Myriophyllum spicatum; – 0.53 ± 0.51 kcal/g), which required more energy to process than was assimilated. TME values for gadwall and ring-necked ducks are currently being estimated and will be presented at the conference.The TME values for these SAV species will allow wetland managers to more accurately evaluate wetland management practices and refine energetic carrying capacity estimates. Moreover, these values contribute a better understanding of the value of emergent marshes containing SAV for ducks, which could potentially provide as much energy as moist-soil wetlands.

Wednesday January 31, 2018 8:20am - 8:40am CST