Canvasback, Aythya valisineria, closeup of drake. Canvasbacks are the largest of a group of widely distributed waterfowl known as pochards, or diving ducks. Large webbed feet on legs located toward the rear of their bodies make them agile underwater swimmers; however, the location of the legs makes land travel difficult, therefore, they are rarely found far from the water's edge. Dorchester Co., MD, December.