Wild and feral ducks should be fed whole grains and birdseed. Bread is actually unhealthy for ducks and can cause malnutrition. Other viable alternatives to bread include shredded vegetables, peas, grapes and bait worms.
Some of the grains that can be healthfully fed to wild ducks are oats, cracked corn, wheat, barley and rice. Rice has been subject to an urban legend. It is said that feeding it to birds causes their stomachs to burst, but that is not the case. Birds such as ducks are able to consume raw rice and other grains without ill effect. Bread, on the other hand, is poor in nutrients and fiber and high in calories. Feeding bread to birds leads to a host of health problems, including fatty liver disease and impacted crop. Ducks can also become aggressive towards humans if overfed bread, and wasted bread can cause mold outbreaks in duck ponds.
Healthy duck treats mimic the sort of diet they would have without any human intervention. Wild ducks naturally feed on a mix of insects and plant material. Foods such as lettuce shreds and raw grain are very similar to the foods wild ducks encounter as a part of their daily foraging. Worms are also healthy for wild ducks and can serve as treats, although they are relatively rich in protein and can cause problems if overfed.