Water vole numbers have risen almost fivefold

The creatures are well-established on the Somerset Levels, but had died out in the north of the county until a breeding programme brought them back.

The water voles were reintroduced to the area as part of a dedicated breeding programme begun by Bristol Zoo, the Environment Agency and the Hawk and Owl Trust.

After years of work, the animals began to be released into the wild in April, and now the number of water voles around the Gordano Valley has leapt to more than 300.

Predator threat

Simon Eyre, of Bristol Zoo, said: "We released 64 water voles in the spring. They have been breeding through the summer and we now have between 300 and 400 of them in the area.

"Each female has five litters a year, and the average litter is five to 11 animals, so they can have 25 offspring a year quite easily."

But Mr Eyre said the creatures were still under threat from predators.

"Because of the numbers of offspring they have, water voles can usually bounce back, but the real problem comes from the American mink.

"Most predators can hunt water voles either on land or in the water, but the American mink can hunt them on land, in the water and in their burrows - once they move in the voles don't stand much of a chance of survival."

The water vole population in north Somerset will continue to be monitored by workers from the three groups involved in the programme.