POLICE and conservationists have launched a clampdown on off-road bikers "riding roughshod" over a North Yorkshire nature reserve.

The Friends of Skipwith Common said the "reckless" driving was threatening several rare bird species and damaging the fabric of the common.

The ancient lowland heath is a Site of Special Scientific Interest and is protected by law.

Friends' co-ordinator Brian Elsey said: "These off-road motorcycles and quad bikes are not road legal or licensed and the antisocial behaviour of the riders is unacceptable.

"They are disturbing nesting birds, some of which are quite rare, such as nightjars, woodcocks and green sandpipers. Once they are disturbed, they move somewhere else.

"There have been nightjars on the common for 100 years and this year we have had none - that's how serious it is.

"They are also damaging the fabric of the common - which is home to some rare flora and fauna - by riding roughshod all over the place.

"Walkers enjoy unrestricted access, but riders don't."

Mr Elsey, of North Duffield, who runs the 100-strong Friends' group, said it was only a matter of time before an innocent walker was seriously injured by a tearaway biker.

He said: "One nearly hit me recently. I have caught several bikers acting illegally and irresponsibly riding off-road, but when approached and advised, many of these riders are aggressive.

"It is a criminal offence to ride on the common and the police have the power to confiscate the off-road bikes and quad bikes.

"We will not hesitate to prosecute persistent offenders."

The common is managed by English Nature, whose conservation officer Julian Small said: "It's a serious problem that has been going on for quite a while.

"These bikes uproot heather and, if they run over Iron Age ancient burial mounds, the damage would be irreversible."

Sergeant Kirk Fletcher, of the local neighbourhood policing team, said: "We are giving the area some attention and if we get registration numbers we will visit riders at their homes.

"Our main worry is walkers getting hurt."

The Friends are urging anyone who witnesses antisocial behaviour to phone the police on 0845 6060247 or Mr Elsey on 01757 288939.

Updated: 10:34 Tuesday, August 16, 2005