Feeding ecology of canvasbacks staging on Pool 7 of the Upper Mississippi River

Foods consumed by canvasback ducks (Aythya valisineria), food availability, and energetic relationships were studied on Navigation Pool 7 of the upper Mississippi River in 1978, 1979, and 1980. Canvasbacks fed primarily upon winter buds of American wildcelery (Vallisneria americana) and tubers of stiff arrowhead (Sagittaria rigida). In 1980, waterfowl consumed 40% of 380,160 kg of wildcelery winter buds on a portion of Pool 7 referred to as Lake Onalaska. Daily energy expenditure based on estimates from the literature suggests that individual canvasbacks require a minimum of 125 g (dry wt) of wildcelery winter buds each day. Extrapolation of use-days and the daily energy requirement suggests that 3,470 ha of wildcelery are required to support a canvasback population represented by 5 million use-days.