Swans are protected under the Wildlife and Countryside Act

A park warden found the young swan and a large carp in the upper pond at Sandall Park on Tuesday. Both had been shot in the head with an air rifle.

Several fish, gulls, a duck, a magpie and a rabbit have been killed or mutilated in the area in the last week, a Doncaster Council spokesman said.

"This cruelty is horrendous," said police wildlife officer Amanda Clayton.

"These animals did not suffer a quick death and we are determined to find out who is responsible."

'Wanton destruction'

She urged anyone with information about the attacks to contact either the police or the council.

Mark Hodson, Doncaster Council's strategic director for neighbourhoods, communities and children's services, said: "This type of behaviour is appalling and we will not tolerate it.

"I urge people with any information to come forward so these mindless yobs can be prosecuted."

Emma Doherty, of the Royal Society for the Protection of Birds' investigations team, said: "Sadly, this type of wanton destruction seems to be all too common, with swans being frequent and accessible targets.

"Vandals should be aware there are severe penalties for anyone convicted of killing wildlife illegally, with up to six months in prison."