Does this remind you of bobbing for apples? When a swan upends itself, it is feeding on the leaves, stems, and roots of aquatic plants. They can easily reach 3-feet into the water to get food. Large feet are helpful in two ways, (1) They disturb the water and cause currents which loosen the plant roots and (2) they provide balance when the swan upends to feed. Swans with human caretakers also get dried corn to supplement their diet.