The name vole is short for the archaic word volemouse, which may come from Norwegian vollmus, from the Old Norse völlr, field and Old Norse mūs, mouse.
Voles are rodents, in the same family (Crecetidae) as lemmings, and like lemmings they sometimes have population explosions. The field vole, Arvicola agrestis, was so plentiful in Scotland, causing so much damage in 1890-1 that the Government appointed a Committee to examine the question. The committee wondered whether the destruction of predators by gamekeepers was responsible, but in true Darwinian fashion, the Scottish outbreak was dealt with by a rapid natural increase in the population of birds of prey. A more recent vole explosion permitted snowy owls to colonise and breed in the Shetland Islands for a number of years.
Voles range in color from gray to brown and in size from three to nine inches long. They have rounded bodies and blunt snouts, small ears and short tails without much hair. Their main food is grasses, but they also eat bark, leaves and insects. There are about 70 species, 40 of which (found in North America, Eurasia and North Africa) are in the genus Microtus, which usually make shallow burrows or runways under vegetation. Confusingly, these are called field mice in North America (in the rest of the world, field mice are a completely different animal). The five species in the genus Clethrionomys nest in shrubs, and those in the North American genus Phenacomys nest in trees and are called tree mice. The Lagarus species found in the western US is called the sagebrush vole, while that found in Russia and Mongolia is misleadingly called the steppe lemming. Voles also are known to strip the bark in a circle around fruit tree trunks, which often kills the tree. They tend not to like human houses, though they sometimes infest barns.
In Europe and Western Asia, the water vole Arvicola amphibus, lives near ditches, streams and rivers. It is the largest British vole, and often mistaken for a rat – in fact Ratty in Kenneth Grahame’s book The Wind in the Willows was actually a water vole, making his nest by burrowing into the river bank. Water voles are not quite as well adapted for life on the water as animals like otters and beavers, so his habit of ‘messing about in boats’ was probably a good one. When alarmed, they make a characteristic ‘plop’ as they drop into the water.
Female water voles give birth to around six young after a gestation period of 20–23 days. The young leave their mother after about 22 days, when she has her next litter. They produce up to five litters from April to September. Despite all this reproductive activity, water vole numbers in the UK have dropped up to 90% in recent years despite their legally-protected status, because of predation from American mink that have escaped from fur farms, and changes in farming and flood control – a much bigger threat to Ratty than the Weasels were. On the principle of ‘the enemy of my enemy is my friend’, the water vole’s new best friend is the otter. Because of pesticide use, the otter population began to decline 50 years ago. However, the recent revival in the otter population is helping the voles because otters have been keeping mink under control.
Water voles like to use a latrine for excretion, and their droppings - cylindrical with blunt ends – are often piled up together near their burrows, which often have grazed areas around the entrance.
Other plans to help water voles by controlling mink include ‘rafts’ made out of wood, polystyrene, oasis and clay, designed to get the mink to climb aboard and leave footprints, alerting watchers to set traps for them. Protective measures include building culverts to allow them to cross underneath roads safely – Durham Wildlife Trust has a ‘Coals to Voles’ project that aims to protect vole habitat in former coalfield areas. In Nottinghamshire, Severn Trent water company bred baby water voles and released them into protected pools at the Kirkby in Ashfield sewage treatment site, microchipping them first in order to monitor their weight and health.
Vole research is indicating that fidelity may be genetic. It seems that less than 5% of mammals are naturally monogamous. This number includes the prairie voles, Microtus ochrogaster, which guard their mate and help rear their young. Meadow voles, Microtus pennsylvanicus, skip blithely from mate to mate and mainly ignore their offspring. Researchers found that meadow voles had fewer vasopressin receptors in their forebrains than prairie voles. To test the theory that the receptor and the behaviour were connected, they gave meadow voles extra vasopressin receptors. The former Don Juans reformed and stayed true to just one mate, even when other females tempted them. Scientists believe that the release of vasopressin during mating acts as a reward, picked up by the extra receptors, making the voles associate those feelings with that mate and encouraging fidelity.
Similar hormones and pathways may be involved in human behaviour, as vasopressin is also released when humans have sex, although in voles the sense of smell is far more important than it is in humans. However, researchers are focusing on implications for autism, where social interaction is abnormal and vasopressin may be involved. Mountain voles – another promiscuous species like meadow voles – have the highest rate of sex of any mammal in the animal world.
Voles use their hind feet and a somersault action to dig their tunnels. Voles’ sense of touch must make up for their poor hearing and vision. Their tails and whiskers are very sensitive to touch and help voles to burrow. Vole teeth, like those of many other rodents, grow constantly, so they need to gnaw to keep their teeth ground to a short enough length. They are not known to hibernate. Voles can carry rabies and also plague-bearing fleas.
Voles in popular culture
‘Vole’ is an increasingly-used nickname originally given to Microsoft by an IT newsletter called ‘The Inquirer’, possibly because a vole’s teeth grow continuously and they have to wear them down or die. The analogy is that Microsoft’s survival depends on stifling the competition.