THREE of the rivers that flow through south Wiltshire are hotspots for one of Britain's most endangered mammals.

For the first time the Wiltshire Wildlife Trust has been able to produce a snapshot of the state of the water vole in Wiltshire, and thanks to the efforts of 60 volunteers who went out surveying the waterways over the summer, the trust has found that the Rivers Avon, Wylye and Nadder in south Wiltshire plus the Kennet, the Bristol Avon and the Kennet and Avon Canal have colonies of the chestnut brown creatures.

The volunteers found water voles at 23 out of the 25 sites they surveyed and by using this information, together with records collected over the past five years, the trust has been able to designate local key areas representing important water vole colonies. The whole of the River Nadder has been identified as a local key area for voles because there are records from every 2km of its length.

"This information gives us a clearer picture of where we must target our work to help voles recover from the disastrous population crash they have suffered in recent years," said the trust's water vole recovery project officer, Beth Nightingale.

"The habitat in these key areas is quite good, but some locations need altered management such as fencing off river banks to protect them from livestock trampling and overgrazing."

Most, if not all, of Wiltshire's rivers would have been home to water voles at one time. One of their favoured habitats is the chalk stream with its clear waters and vigorous plant communities, including water crowfoot and watercress. But numbers in Wiltshire have dropped by 30 per cent over the last decade.

Despite this, the county is still a stronghold of the vole compared to the rest of the nation, where populations have declined by 94 per cent over the same period, making it not only our fastest declining mammal, but also one of our rarest. The two main causes are habitat loss and predation by the American Mink.