Diet Selectivity of Gadwalls Wintering in Alabama

The nutritional quality of Eurasian watermilfoil (Myriophyllum spicatum) as a food source for waterfowl has been questioned. We therefore studied dietary preferences of gadwalls (Anas strepera) at Guntersville Reservoir, Alabama, where milfoil is the dominant submerged aquatic plant and large numbers of gadwall occur in winter. Standing crop biomass of subinersed aquatic vegetation in the reservoir declined 97% throughout winter (P 0.05). Consumption of large milfoil stems (>2 mm wide) was less than that available (P 0.05). Various parts of the milfoil plant differed nutritionally. and by selectively feeding on these parts and other foods, gadwalls were able to subsist on a diet dominated by milfoil.