THE harvest mice released into the North-East countryside yesterday were not to know it, but they were the pioneers in a project to reverse decades of destruction by humans.

Weighing less than a two pence piece, the creatures were the first in a regional reintroduction programme which started on Teesside, where the animal was wiped out by loss of habitat.

Fifteen males and 15 females were released into a specially designed outdoor pen at Cowpen Bewley Woodland Park, near Billingham, as part of a project by Stockton Borough Council.

Harvest mice still enjoy a wide distribution in southern England, but there are very few remaining colonies in the North-East.

There are two sites in Northumberland, sporadic reports along the River Tees near Darlington and a report from the Derwent Valley, in County Durham, in 1986.

Over the past year volunteers have bred 200 mice from eight provided by Chester Zoo and yesterday the first 30 were given a taste of freedom.

Ian Bond, project leader and a countryside warden with the council, said: "We selected the site because the kind of grassland habitat is well suited for the mice. They will stay in the pen to allow them to adapt to their surroundings and if that is successful, will be released in August.

"It is exciting to see them in the pen, but it is just a step along the way."

He said there were reports of harvest mice from neighbouring Greatham, and Billingham Beck, but none from Cowpen Bewley.

Mr Bond said he hoped the animals would create an established breeding population, and a second, as yet unnamed nature reserve, on Teesside, had already been chosen for a further release.

Yesterday's event was attended by Travis Bacon, Katie O'Hara and Ben Jaab, pupils at Harrowgate Hill Junior School, in Darlington, who have cared for some of the mice.

Katie said: "We started with just two and we have bred 35. I don't think anyone really knew much about harvest mice until they arrived. Everyone is interested now."

Schoolteacher Joanne Vest said: "The kids are really excited by the project, they love it."

The £600 release pen was sponsored by Teesside chemical company Air Products, using money won by its Billingham site in a competition in which the company sought its most environment-friendly operation worldwide.

Harvest mice, among the world's smallest rodents with a head and body just 64mm long with the tail doubling their size, have traditionally been associated with cornfields.

Naturalists say many cornfields are now reaped by machines then ploughed for replanting, which means harvest mice can no longer make them their home all year round.

They say stubble burning and the removal of scrub and hedgerows on farmland have also had a severe effect, as has loss of grassland to urban development