The water vole or water rat, (Arvicola terrestris), first achieved notoriety as "Ratty" in the Wind in the Willows. "Ratty", despite his name, is the largest British member of the vole family. In 1908, when Kenneth Grahame wrote the Wind in the Willows, the water vole was a widespread and familiar inhabitant of British rivers, streams and ponds.

However, since the 1900s the water vole population has suffered a gradual long term population decline punctuated by two periods of accelerated loss, the first in the 1950s and again during the 1980/90s. By 1990 approximately 70% of sites formally occupied by water vole had been lost and at the current rate of decline it is predicted that by the year 2000 only 6% of all formally occupied sites will remain.

If this prediction is realised then the water vole will have undergone the most dramatic decline of any British mammal this century.

The principal cause of the water vole decline is considered to be excessive predation brought about by habitat degradation. The water vole is highly dependent on bankside vegetation for cover and food, so that in areas where the bankside vegetation has been cut or otherwise removed the water vole becomes easy prey for a whole host of predators, including the notorious mink.

Dredging operations and engineering works can also completely destroy the water vole's burrows and effectively prevent future re-colonisation. Furthermore, as water voles' colonies become increasingly isolated it reduces the chance of their populations being supplemented by individuals from elsewhere. The consequence of such isolation is an inevitable increase in the risk of extinction and so an increased rate of site loss.

The seriousness of the plight of the water vole is now highlighted by the fact that the species is one of only nine mammals listed on the UK's Biodiversity Action Plan and by the fact that the water vole has recently received legal protection under Schedule 5 of the Wildlife and Countryside Act.

A principal requirement of the national water vole action plan and recovery plan is for local surveys throughout the UK. Grants from the Sunley Wildlife Action Fund, Environment Agency and the Naturesave Trust enable the Dorset Wildlife Trust to carry out a comprehensive county wide survey. The objectives of the survey are to provide the first accurate county distribution of water voles, to assess the quality of the habitat available and to determine the principal threats to the remaining populations.

The survey is being carried out on the ground by a team of fifty or so trained volunteers who have all been assigned stretches of river on which they will carry out detailed habitat surveys. In addition the project will make a series of appeals for public sightings which will be used to compile a Dorset Water Vole Site Register. These casual records are being supplemented through "Water Vole Watch" - a national survey being run simultaneously by Wildlife Watch, the junior arm of the Wildlife Trusts.

The aim of the project will be to visit all reported sites to both confirm the record and promote awareness of water vole conservation.

By identifying the core water vole sites and key isolated colonies the survey will also enable the effective targeting of more sensitive management including habitat enhancement measures. It is hoped that the information derived from the project combined with the development of an effective partnership between the Trust, Environment Agency, riparian owners and planning authorities will help to ensure the recovery of the water vole throughout Dorset.

Contact:

Guy Corbett Marshall
Dorset Wildlife Trust
Brooklands Farm, Forston, Dorchester DT2 7AA
Tel: 01305 264620