Wildlife rescue members were called to Langney Pond on Saturday afternoon by concerned members of the public, who saw children trying to kick a swan in the head.
The swan had tried to protect itself by hiding in bushes and had to be rescued by members of the East Sussex Wildlife Rescue and Ambulance Service.
The swan was transferred to Princes Park and it was while rescuers were there, founder Trevor Weeks noticed another swan had a swollen head.
He believes the bird had been shot.
"On examining the swan there was a clear entry and exit wound so it was rushed to the vets for further assessment," said Mr Weeks.
The swan was transferred to a special swan sanctuary in Surrey, and the incidents have left rescuers angry.
Mr Weeks said, "I am sick and tired of picking up the pieces where humans get some sick pleasure out of abusing wildlife.
"Honestly, what pleasure do people get out of shooting a swan? These people must be sick.
"WRAS volunteers are running around left, right and centre and I take my hat off to them for all the volunteer hours they put in clearing up after irresponsible people."
Over the same weekend a swan was run over at Hove Lagoon and a second bird was attacked by a dog and later died.

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