If the swan is new to the area, wild or captive, it is not going to eat from you until it gets to know you. If you have a pond on your property, it will find its own aquatic vegetation and other nutrients from the water habitat. You will need to gradually introduce yourself or throw some bread, lettuce, cracked corn and poultry layer pellet into the pond and let the bird eat while you are not around. Eventually, it will associate you with the new morsels.

If there is no pond or other water source and it is refusing to eat, you need to safely capture the bird and transport it to an avian waterfowl/swan veterinarian or other wildlife rehabilitation facility for evaluation and possible treatment. The Regal Swan