The water vole

Kelly Hollings, Restoring Ratty Project Officer for Northumberland Wildlife Trust, explores the habits of these much-loved mammals.

Water voles are Britain’s largest voles, with fully grown adults reaching lengths of 20cm (plus a 12cm tail) and weighing up to 350g. They are charismatic little creatures with a round face, a blunt nose, a short furry tail and glossy dark brown or black fur. Water voles were popularised by the well-known character Ratty in Kenneth Grahame’s ‘Wind in the Willows’, who, despite his misleading name, is not a rat but a water vole.

‘… A brown little face, with whiskers. A grave round face, with the same twinkle in its eye that had first attracted his notice. Small neat ears and thick silky hair. It was the Water Rat!'
Kenneth Grahame, Wind in the Willows

In spite of their name, water voles are not particularly well-adapted to aquatic life. They have evolved to live alongside water to aid their escape from predators. Their characteristic ‘plop’ is the sound of them diving into the water to escape any would be predator and to access the underwater entrance to their burrow. But they are clumsy swimmers without the rudder-like tail or webbed feet evolved by other water-loving creatures. Away from water – and where safe from predation, water voles can live completely fossorial (burrowing) lifestyles and in fact they do in a well-known location in Glasgow!

Burrowing and breeding

Water voles live in burrows that they build by biting into the banks with their very strong, enamel-coated orange teeth. These burrows can be very complex and consist of nesting and nursing chambers, with two entrances, one on the bank and one underwater. A water vole burrow is roughly the width of a balled-up fist or a tennis ball. During the winter months, water voles are tolerant of each other and live together in family groups in their burrows; but this all changes in the breeding season, when they become very territorial!

The breeding season begins in April and continues until October. Water voles are extremely successful breeders – they need to be to replenish the numbers lost during winter; when up to 80% of water voles perish, mainly as a result of starvation. Gestation for a female vole is only 23 days! Her babies (pups) leave the nest after three weeks and are themselves able to breed at 15 weeks old. One female water vole can have between five and six litters in a year, with between 3-5 pups per litter, meaning that one female water vole could have 25-30 babies in one breeding season – poor thing! Water voles have a very short lifecycle and don’t usually live for more than one winter.

The breeding season is also the peak time to survey water voles, as the territorial females leave piles of droppings (latrines) to mark the edges of their territories. Finding latrines is the water vole surveyor’s dream! If you think you have water voles in your local patch of rivers or streams, have a look for their latrines, burrows and piles of vegetation or food stores, which are pieces of vegetation measuring between 4-10cm, bitten off with a 45° angle at their tip.

Always eating

Water voles need to eat up to 80% of their own body weight every day in order to stay healthy. Their diet consists of mainly grasses and waterside plants, as well as twigs, bulbs, roots and fallen fruit. They aren’t too picky and have been recorded feeding on up to 220 different plants. Although they are described as herbivorous, a female feeding young will eat a dead water snail or fish if she comes across one, to boost her protein levels. 

Water voles in decline

Sadly, water voles are one of the UK’s fastest declining mammals. Up to 90% of the population has been lost since the 1970s; part of a longer-term decline stretching back to the Middle Ages. The reasons for this decline include habitat loss and fragmentation (their habitats being broken up into smaller, disconnected chunks). Examples of this include overgrazing and mowing of riverbanks and canalisation of streams.

It is well-known, however, that the American mink is the key driver behind the more recent decline of our water voles. Mink were introduced into the UK in the 1960s after fur farms were closed. In their native home of North America, muskrats form a major part of the mink’s diet; in the UK, there are no muskrats and instead water voles, which resemble muskrats, form a major part of their diet. 

Water voles are at the bottom of the food chain, and have a great many predators. They are eaten by otters, buzzards, owls, and foxes to name just a few! But these are all native animals and the water vole can cope with these natural predation pressures by breeding rapidly and escaping into their burrows. However, a female mink is slim enough to follow the water voles into their burrows and predate entire populations. 

Fortunately, it’s not too late for the water vole! Wildlife Trusts across Britain have been working to help water voles recover, restoring their habitats and even reintroducing them to areas where they were once lost. 

Restoring Ratty

Surveying the distribution of water voles is essential to securing their survival. At Hampshire & Isle of Wight Wildlife Trust we lead on collating and mapping data from across the country about where water voles are, through the National Water Vole Database and Mapping Project. This porject also helps map the impact of American mink, one of their key threats. 

The latest report and maps, published in 2020, show we can - and have - made a positive difference by starting to reverse the decline in distribution of water voles. But their current distribution remains just a fraction of what it was 60 years ago, and some areas continue to show a contraction in range. Our continued monitoring work ensures data is up-to-date and we are doing all we can to protect water voles. Creating a Nature Recovery Network across sites where they are doing well and the wider countryside is vital.

Water voles are also an iconic species of Hampshire's chalk streams - they enjoy the rich vegetation and steady flow that these special waters provide. Unfortunately even here they have come under threat from the American mink population and other environmental pressures.

One way we're tackling this is through the Watercress and Winterbournes Landscape Partnership Scheme. As well as improving the wildlife habitat of our chalk streams, and reducing the pressures upon them, we're monitoring their water vole populations to better assess their wellbeing.

The Trust also supports the Meon Valley Water Vole Project, led by the South Downs National Park Authority. The project saw 2,548 water voles released within the Meon Valley, including at St Clair’s Meadow Nature Reserve. The latest surveys show that water voles are now established on the river and doing well, and we hope they will continue to spread from release sites to new parts of the river.

Water vole feeding

© Tom Marshall