Underwater Foraging Behavior of Canvasbacks, Lesser Scaups, and Ruddy Ducks

We observed the underwater behavior of captive Canvasbacks (Aythya valisineria), Lesser Scaups (A. affinis), and Ruddy Ducks (Oxyura jamaicensis) while they foraged on a variety of food items in a large aquarium. Canvasbacks probed into the substrate with the bill and body oriented perpendicular to the bottom. Lesser Scaups and Ruddy Ducks strained food items from the substrate surface by moving their bills in short, lateral arcs while rapidly opening and closing their mandibles; their bills and bodies were oriented at a 35 to 45° angle to the substrate. Scaup also fed by grasping prey in the water column, where they appeared to locate prey visually. Ruddy Ducks did not appear to select prey visually. The species also differed in their underwater locomotory behavior and postures; these differences probably are related to the prey and conditions typically encountered by each.