Police are hunting thugs who shot a swan in the head with an air rifle on a pond in Burgess Hill.
Residents alerted wildlife experts after spotting the male swan in a distressed state.
Lindy King and Trevor Weeks from the East Sussex Wildlife Rescue and Ambulance Service were called to Mill Pond on the Bedelands Farm Nature Reserve and captured the bird, which has a mate and a cygnet.
Mr Weeks said: "He was very lethargic and had not eaten for three days. He didn't look right and residents had become very concerned about him."
They transported the swan to the Swan Sanctuary in Egham, Surrey, where the bird underwent an X-ray which revealed the extent of the injuries which almost caused its death.
Two airgun pellets were lodged in its head, one behind its right eye and another at the back of its skull in the spine.
Vets decided not to remove the pellets because the operation was too dangerous and might have killed the bird.
It is now undergoing drug treatment, but will have to be returned to the pond as soon as possible.
Anyone found guilty of killing or causing suffering to swans faces a maximum fine of £5,000 and six months in prison.
Mr Weeks said: "The swan would have died an agonising death."
PC Chris Finch, Wealden police division's wildlife liaison officer, is appealing for information.
Residents are also mounting "swan watches". A police spokesman said: "People will be keeping an eye on things and if anyone has any information they should call us."
Sussex Police can be contacted on 0845 6070999, while East Sussex Wildlife Rescue and Ambulance Service operates a 24 hour helpline on 078150 78234.
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