At least three adult herons and several chicks have been killed with a shotgun.

Last night wildlife groups condemned the attack on the protected birds - which also resulted in the destruction of three nests at a North Yorkshire heronry.

"I can see no reason why anybody would want to attack such lovely birds, that give so many people such enjoyment," said Graham Madge from the RSPB.

"Herons are big and ungainly when they're in the treetops at their nesting site. They're not good sport for anyone to take a pot-shot at."

One teenager armed with a shotgun was spotted close to the heronry near West Burton, Wensleydale, but left when a local farmer arrived. The incident took place in May but only came to light after an investigation by The Northern Echo. The matter has now been reported to police who are investigating.

Around 12 pairs of herons nest at the heronry, built in larch trees, every year.

The full extent of the attack will not be known until nesting time next year, bird experts say.

Heather Holmes, North-East spokesman for the RSPCA, said herons were protected under the Wildlife and Countryside Act 1981. "We take a very dim view of people killing wild birds," she said.

"It is horrifying that someone would shoot them for target practice or even for fun.

"This is a sickening attack and we would urge anyone with information about this incident to contact ourselves or the police."

Anyone found guilty of killing a heron could be fined up to £1,000 or face six months in prison.

This is the second known attack on protected wild birds in Wensleydale in recent years.

In 2003, three rare peregrine falcon chicks were shot in their nest in a quarry near Leyburn.

The quarry owners offered a £1,000 reward for information leading to the arrest of the offenders, but nobody was ever caught.

Shocking figures released by the RSPCA this week put the north of England bottom in a cruelty to animals league table.

Anyone with information should call police on 0845 6060247.