Ecology of wintering Gadwalls and American coots at Guntersville Reservoir, Alabama

I investigated winter ecology of Gadwall (Anas strepera) and American coot (Fulica americana; hereafter "coots") following the 1990 release of grass carp (Ctenopharyngodon idella) into Guntersville Reservoir, Alabama. Herbivory of aquatic vegetation by ducks and coots, and the relationship between duck and coot densities and abundance of aquatic vegetation was studied November-February 1991-92 and 1992-93. Density of ducks and coots was positively related to abundance of aquatic vegetation (predominately Myriophyllum spicatum) in both years. Herbivory by ducks and coots reduced biomass of aquatic plants in both years, but the intensity and timing of herbivory varied between years.; Foraging niche dynamics of Gadwalls (Anas strepera) and coots was studied October-February 1992-93. Diet and feeding behavior niche breadths were negatively related to food abundance for both species. Diet, feeding behavior, and microhabitat niche overlaps were positively related to food abundance, consistent with niche partitioning between potentially competing species.; Diet selectivity of Gadwalls relative to nutrient content of food items was studied November-February 1992-93. Estimated nutrient content of the diet did not vary over time, whereas estimated nutrient content of available foods did. Food preference generally was unrelated to nutrient content of food items. In January, when available protein was lowest, food preference was positively related to protein content of food items.; Carcass composition and gut morphology were examined October-February for coots and November-February for Gadwalls. Masses of carcass and fat in Gadwalls and coots peaked in mid-winter (December) and declined in January, similar to other waterfowl species. Ambient temperatures and food abundance were lowest in February. Because lipid and carcass mass increased (coots) or remained the same (Gadwalls) from January to February, mid-winter declines in fat and carcass mass were attributed to endogenous mechanisms, rather than unfavorable environmental conditions.