There could be any number of issues from lead, botulinum or other poisoning, to soft tissue injury from another swan, predator or sprain from entering or exiting the water. She may be in pain. You need to get her to an avian (bird) waterfowl veterinarian. The veterinarian can provide her with chelation to remove lead or other poisoning ( you need toxicology tests to check the presence of toxins) antibiotics or anti parasitic-fungal medications based upon blood tests.

The veterinarian can also use a medication such as Medicam to help with pain. If there is a soft tissue injury, pain management is very important and can be the reason for not eating. Arthritis could also be a factor. Note: if any pain medication is prescribed, you need to keep the swan indoors on a soft substrate so she does not hurt her legs. Supervised swimming and bathing has to be provided so she does not get drowsy from the medication and drown. A one-time B-12 has been used in England and other areas to jump start the appetite. If you have a College of Veterinary Medicine in your state, they will be able to refer you to a waterfowl veterinarian. We hope this helps. Let us know how she is doing. The Regal Swan