Usually shy and secretive, many of us in the UK have likely never encountered a real, live water vole. And even those of us who have come across one may only have heard the telltale ‘plop’ of an animal as it enters a canal or river and swims away to the safety of its burrow. This lack of visibility isn’t just down to their shy nature, though. It is also a result of catastrophic population declines over the last 50 years and the species’ consequent disappearance from many of its former haunts. They are now the UK’s fastest declining mammal and Red Listed as a species at risk of extinction. As important ecosystem engineers, losing water voles doesn’t just impact them, either, but negatively affects the habitats they live in. But why has this small mammal declined so much, and what can be done to help it?
The Riparian Rodent
Water voles are small, usually chestnut brown mammals with a blunt nose and small ears. The tail is fur covered and about half the length of the head and body. Although called Ratty in Kenneth Grahame’s famous work, The Wind in the Willows, and often mistaken for them (or vice versa) when spotted swimming along a water course, water voles are categorically not rats. Both species are, though, rodents, along with mice, squirrels and beavers. This taxonomic order is defined by a pair of continuously growing, chisel-like incisors in both the upper and lower laws. Most eat grains, seeds and vegetation, the gnawing of which ensures that the ever-growing teeth are worn down enough to keep them a manageable length. Water voles are no exception and keep their teeth from growing too long through both their plant diet and by using them to excavate long underground burrows.
They can be told apart from other vole species by their size. Water voles are approximately twice the size of the UK’s two other vole species, bank and field voles. Consequently, water voles are much closer in size to brown rats than their cousins. Although all our voles are excellent swimmers, water voles are also most likely to be seen actually in the water. Rats are also good swimmers and are often seen in canals and rivers so present more of an identification issue. However, rats have relatively long, hairless tails compared to the water vole’s shorter, furred one and have pointier noses and proportionately larger eyes and ears. Rats also tend to swim more visibly at the water’s surface unlike water voles who swim submerged.
Out of the Ice Age
Interestingly, Scottish water voles are more likely to be much darker in colour, sometimes almost black, as well as slightly smaller than their Welsh and English cousins. This is because they are descended from darker voles from the Iberian Peninsula and are genetically distinct from water voles in England and Wales. Research shows that voles in Scotland recolonised what is now Britain from Iberia at the end of the last Ice Age around 15,000 years ago. At this point in time, Britain was still connected to mainland Europe. Once sufficient vegetation had managed to gain a foothold in the region as the ice retreated, this connection allowed flightless organisms like the water vole to return, as well.
The first water voles to recolonise what is now Britain only had a relatively short respite, however. Around 13,000 years ago, a shorter, less intense mini glaciation occurred that lasted for approximately 1,000 years. Although it had nowhere near the impact of the last full glacial period, it seems that this cold spell did reduce water vole numbers here to a few isolated populations. When this mini glacial period ended, about 12,000 years ago, water voles from eastern Europe then arrived across the still extant land bridge and quickly spread. The remaining inhabitants from the earlier colonisation were then effectively pushed back to Scotland. Descendants of the second wave of water voles tend to be the classic chestnut brown colour we associate with the species.
Vole Life
Across much of the UK, water voles are usually associated with water bodies such as rivers, streams, ditches, canals, lakes and ponds. In these sorts of habitats, they build long, multi-passaged burrows in the bank, removing soil with those sharp, chisel teeth. At least one entrance hole is usually placed below the water line. These underwater holes allow a quick escape route should danger threaten. Burrows also usually consist of different levels so that the highest nesting chambers are safe from flooding. The species isn’t always as tied to water as its name suggests, however. In some places, including upland areas of Scotland, urban sites and many parts of mainland Europe, water voles are what’s known as fossorial and live in terrestrial burrows. One such population lives in underground tunnels in the East End of Glasgow, some distance from the nearest water. Researchers think that habitat loss has forced the voles to adapt in this way, although this terrestrial lifestyle is much more common on the Continent.
Wherever they live, water voles create areas of short vegetation called lawns at their favoured eating spots. These are usually right outside a burrow entrance. Because they need to eat up to 80% of their body weight a day, their eating habits unsurprisingly remove a substantial amount of plant matter, hence the obvious clipped areas. Nibbled stems often accumulate in large piles and usually have a distinctive 45° angle to the ends where chewed. Although they will eat a wide variety of plant species, grasses form the bulk of their diet. This preference helps less dominant plant species to grow as it reduces the grasses’ stranglehold. Water voles use regular latrines for their cigar-shaped faeces, another visible clue to their presence. During the breeding season, which runs from early April to October, water voles are extremely territorial. Both males and females defend their stretch of the riverbank against rivals. Females may have between three and four litters of up to five young per year, with pups born earlier in the season able to breed themselves the same year. The many dangers they face, including predation or winter starvation, means that the average lifespan is no more than 18 months.
The Vanishing Water Vole
With a single female able to produce up to 30 babies a year, you might think that whatever the threats, water voles must have no problem maintaining a reasonably sized population. And until the second half of the 20th century, this was indeed true. In fact, their rapid reproduction rates meant they were abundant across much of the UK. This is despite the fact that they are predated by a large range of other species, including foxes, herons and pike, and up to 50% of water voles may also starve during harsh winters. That ability to balance any losses was to change in the second half of the century, though, and they have undergone a staggering 97% decline over the last 50 years. Habitat loss, much of it connected to the intensification of farming and associated drainage after World War II, has been a major factor. Populations became increasingly isolated from each other, inhibiting their ability to disperse and breed.
The other major cause of the water vole’s decline over the last 50 years is the American mink’s arrival on these shores. This small mustelid is a relative of stoats and otters, and large numbers were farmed for their fur in the UK from the 1920s onwards. Some escaped into the countryside by themselves, and breeding in the wild was confirmed in 1956. These animals were supplemented as a result of releases by animal rights activists in the 1980s and 90s. They have subsequently spread across much of mainland Britain and are classed as an invasive non-native species. Mink are good swimmers and highly efficient predators. Crucially, females are small enough to easily get into water vole burrows after their prey. This, combined with the fact that water voles have not lived alongside them for long enough to adapt to their presence, means a single female mink can destroy a whole colony in a short space of time.
Help for Ratty
The water vole’s perilous status means that it has been, and continues to be, the subject of various research and conservation measures in the UK. In legislation terms, under the Wildlife and Countryside Act 1981 in England it is illegal to intentionally kill, injure or take them, or to possess one, living or dead. It is also illegal to intentionally or recklessly damage, destroy, obstruct or disturb a place of shelter or refuge. (Bizarrely, in Scotland, only shelter and refuge sites are protected whilst the voles themselves are not.) Water voles are also a Priority Species under the UK Post-2010 Biodiversity Framework. From a planning perspective, if biological records show that water voles have been recorded at a proposed development site, or it includes suitable habitat, then a water vole survey must be carried out. If animals are present, then ecologists can decide how to mitigate for any negative impacts. Where mitigation isn’t possible, voles may be relocated as a last resort.
Along with legislative aid, teams of passionate researchers have dedicated their lives to helping this charismatic, little rodents. Armed with the perfect temporary water vole receptacle, the humble Pringle tube, they have spent countless hours in the field monitoring them with a view to turning the tide. This has not been without its own conflicts, however. Scientists led by Dr Tom Moorhouse discovered, for example, that radio-collaring females put enough stress on them to change the ratio of male to female offspring they produced. This could have had a disastrous consequence for monitored colonies if the collaring was continued. What is clear from all this research, though, is that, ultimately, although habitat restoration is also key, an ongoing programme of mink trapping will have the biggest impact on water vole numbers in the UK. No conservationist relishes the thought of killing an animal, however negatively it is affecting another. But, sadly, all the habitat restoration in the world will not save the water vole while mink remain in the UK.
Hope for the Future
Although mink in the UK have themselves declined over the last quarter century, until recently, they have been difficult to eradicate. This is because any animals missed allow the population to quickly recover. New methods, though, combining effective lures, DNA mapping and traps allowing for quick and humane dispatch of the mink, are producing extremely promising results. If funding allows this work to be scaled-up, we might be able to remove mink entirely at least from some water vole territories. Some researchers also believe that the otter’s recovery in England and Wales is helping as they seem to outmuscle their smaller cousin. As ecologists, we can also continue to help water voles through careful surveying of proposed development sites. Fossorial colonies are particularly vulnerable to development because they are more likely to be on land suitable for building than riparian populations are.
And saving water voles won’t just help the species itself. Water voles are important constituents of freshwater environments, acting as ecosystem engineers with their burrow digging and lawn-keeping. As well as helping to move nutrients around through the soil with their tunnelling, their holes provide shelter for a host of other small organisms. By eating lots of grasses, as well, water voles help less dominant plant species to flourish in their place. Hopefully, a combination of continued habitat restoration, research, surveying and successful limiting of the impact of mink can help restore this incredible little creature to more of our waterways.