Other varieties of grains that are fed to waterfowl include oats, millet, barley and rye. Important food items that are often overlooked are greens and vegetables. It is a necessity for swans and geese to feed on greens such as leaf or romaine lettuce, and if space allows, they love to graze on the grass. We feed carrots, potatoes and squash that is grated at least once a week. These veggies are usually fine, just a few dents or tears, but be sure to wash them and check them over before offering them to your birds.
Many breeders also offer live food such as mealworms or feeder fish to breeding and growing birds.
Both of these are readily available at any pet store. Breeders of Mergansers and other diving ducks often supplement their diets with small kibble dog food, which is high in protein and great for growing ducks. Drinking water is very important in the digestive process. Waterers seperate from the swimming water is changed daily. These can be used to administer medications and vitamin supplements.