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Reintroducing Ratty

PUBLISHED: 13:54 18 August 2015 | UPDATED: 14:13 18 August 2015

Almost 200 water voles have been transferred to Thorley Wash. Photo: Dave Kjaer

Almost 200 water voles have been transferred to Thorley Wash. Photo: Dave Kjaer


Water voles have been rounded up and rehomed at Thorley Wash nature reserve in an ambitious project to reintroduce the endangered animal to the river Stort. Wildlife Trust water vole conservation officer, Martin Ketcher, explains

Water voles have been lost from several Hertfordshire rivers. Photo: Paul ThrushWater voles have been lost from several Hertfordshire rivers. Photo: Paul Thrush

In a joint project between Herts and Middlesex Wildlife Trust and Essex Wildlife Trust, almost 200 water voles were transferred from a reserve in Essex to Thorley Wash reserve near Bishop’s Stortford in Herts. The voles were soon to find themselves ‘homeless’ following plans to flood their territory in Fingringhoe Wick reserve near Colchester as part of an inter-tidal habitat creation project.

The 188 animals were collected and transported to Thorley Wash where they were released mostly in male/female pairs, some singularly and three mothers with young, over two days in June. The Herts and Middlesex Trust site was chosen for the project because of its abundant and well-established habitat suitable for water voles. Once established, it is hoped the animals will spread along the corridor of wet flushes, ponds, channels and the main Stort Navigation.

The much-loved water vole, the inspiration for Kenneth Grahame’s Ratty in The Wind in the Willows, is in danger of becoming more fiction than fact. Once abundant in our waterways, they have suffered a catastrophic population decline in recent decades, to the point where they are now the UK’s fastest declining mammal. This steep decline is partly due to loss of river bank habitat but is chiefly caused by mass predation by invasive American mink. It is very difficult to estimate the mink population in the county but it is highly likely there are mink on all its rivers. Efforts by approved experts to trap (in cages) and then destroy mink are focussed on areas where water voles are still present.

Without urgent action it is possible water voles could soon become extinct within Hertfordshire - they have already been lost from several Hertfordshire rivers. Once populations go, problems with habitat loss become much more significant and remaining populations become isolated and the need for conservation management on the whole river becomes important if the species is to recolonise. 
The Stort was chosen as a release site because of coordinated and ongoing efforts to monitor and control mink along the whole of the river from north of Bishop’s Stortford down to the confluence with the river Lea. Although there is some recent evidence of water voles spreading gradually in some places across Hertfordshire and Middlesex this is very limited. The opportunity to reintroduce the species on such a large scale is a tremendous boost to their overall conservation.

American mink - one of the greatest theats to water vole populationsAmerican mink - one of the greatest theats to water vole populations


Water vole facts

Size: 20cm head and body, 12cm hairy tail.

Weight: 250 grams.

Diet: More than 200 different plants.

Habitat: Ponds, rivers, lakes, canals and ditches

Population: have fallen by over 90 per cent in the last century and as a result, the water vole now needs protection nationwide.

Threats: Destruction of natural river banks and wetlands has resulted in a huge loss of colonies as well as the isolation of remaining populations. By far the biggest threat facing water voles is predation by the non-native American mink. This species can wipe out an entire water vole colony in a matter of weeks.

Water voles in Herts: Herts and Middlesex Wildlife Trust has been working to conserve water voles and their habitat and fortunately, the water vole is still present in Hertfordshire, although only in small numbers. Key strongholds are along the River Chess in the west, and rivers Stort and Lea around Hertford, Ware, Hoddesden, Broxbourne and Cheshunt in the east.

How to help: HMWT volunteers are trained to survey stretches of river bank to look for evidence of water voles; around 80 are actively involved. The trust also coordinates mink control in the county and provides equipment and advice to householders, landowners, gamekeepers, fishing clubs and others willing to monitor and control mink. Or simply join the HMWT.

To keep up to date with the voles’ progress and for more information on ways to help wildlife, visit


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