Some of the foods eaten by swans include: sedges, pond weeds, insects, aquatic beetles, snails, and shrimps. They are large water birds that can live approximately 50 years in domestication. They have a wing length of about 1.5m and weigh about 8 to 10 kg.
Swans eat insects, aquatic beetles, snails and fresh water shrimp. Basically, any little critter they find in the water they eat. They will also eat many aquatic plants. You can find more information here: http://wanttoknowit.com/what-do-swans-eat/
Swans will eat wigeon grass, tadpoles and insects, while they are living on fresh water. If they are on the saltwater, they will eat green algae, grass,tadpoles and insects.