The British water vole is the largest of the Vole family found in the UK with adults reaching 22cm in length not including tail and weighing up to 300g. They are sometimes locally known as a water rat the species is clearly a member of the Vole family with a round nose and face and small ears as well as a short furry tail. The majority of UK animals have a red brown coat but black fur is not uncommon especially in Scotland. They are well adapted to the water with their fur trapping air that helps to insulate them while swimming and flaps of skin on the ears to prevent water entering the inner ear.

The breeding season is between April and September with females battling for ranges and scent marking their areas during this period. These territorial fights are marked by teeth gnashing and thumping of tails as well as scratching with fore paws. Depending on conditions up to 5 litters of pups are produced, each one having between 3 and 7 young.

Habitat

Water Voles can be found throughout Europe and into Russia. They favour lowland areas near water. They create complex burrow systems often in soft river banks. These burrows normally have an underwater entrance which prevents predators gaining easy access and have several layers in case of flooding. Where there are above water entrances they can be spotted by looking for areas of short grass around them due to the voles eating the grass.

Prey

Water Voles are omnivores eating mainly waterside plants in particular the roots and bulbs as well as grasses. They occasionally store nuts and acorns as well as eating slugs, snails, small fish and freshwater shellfish when available. Like many small mammals they need to eat a great deal each day and can eat 80% of their own weight a day.

Water Voles are hunted by predatory birds such as Buzzards, Grey Herons, and Tawny owls. They are also preyed upon by Grass snakes, Stoats and Weasels but in recent years the major predator has been the American Mink.

The Mink is an introduced species and is able to effectively hunt vole on land or water and is a capable swimmer allowing it to enter vole burrows via the under water entrance. The Mink, use of rodent poisons and loss of habitat as banks as modified for drainage and flood defence has lead to a massive fall in Water Vole numbers with possibly as many as 96% of former colonies now extinct. Ironically increasing Otter numbers may save the Water Voles as the Otters drive out the Mink but don’t eat Water Voles.

Under the Wildlife and Countryside Act 1981, it is an offence to disturb, obstruct or damage water vole burrows
Advice on water voles for planners and developers can be found here

http://www.naturalengland.org.uk/ourwork/regulation/wildlife/species/watervoles.aspx