True metabolizable energy of moist‐soil seeds among dabbling duck species

Abstract

True metabolizable energy (TME) assays were first developed to refine poultry diets but have since been adapted by wildlife biologists and conservation planners to determine the assimilable energy within natural wetland foods (i.e., seeds, invertebrates, vegetation) for waterfowl. Bioenergetic models incorporate TME values to quantify the energetic carrying capacity of wetlands. Prior TME research focused on the food items commonly found in mallard ( Anas platyrhynchos ) diets, leaving uncertainty in bioenergetics modeling as to the carrying capacity of other dabbling duck species in combination with a wider range of moist‐soil plant seeds consumed by waterfowl. We collected 287 TME _N (nitrogen corrected TME) feeding trial samples between August and March 2020–2022 to quantify TME _N for 8 moist‐soil plant seed species ( Cyperus erythrorhizos , Cyperus iria , Leptochloa panicoides, Panicum rigidulum , Polygonum hydropiperoides, Polygonum lapathifolium , Sesbania herbacea, Sida spinosa ) among 3 species of dabbling duck (mallard, northern pintail [ Anas acuta ], and green‐winged teal [ A. crecca ]). We found TME _N values varied among duck and seed species (min–max = −0.29–2.58 kcal/g), with northern pintail values generally being 1–2 kcal/g lower than mallard and green‐winged teal. Our results indicate that bioenergetics models could be improved by incorporating species‐specific energy supply estimates, customized by species composition for the region or area comprising the planning unit. Moreover, management practices can be focused on providing plant species most beneficial to target species or groups of ducks representing the expected species composition in a management unit using this new information that illustrates the variability in assimilable energy across plant species and for dabbling duck species other than the generalist mallard.