One of four species of British vole - the others being the Bank Vole (Clethrionomys glareolus), Field Vole (Microtus agrestis) , and Water Vole (Arvicola terrestris) . This animal has much to commend it, although to describe it (as I have done) as a British species is stretching the truth somewhat because it is found wild only on Guernsey and on various islands in the Orkney archipelago. Curiously, the voles of Orkney seem to share more affinities with the voles of the Balkans and France than they do with the geographically closer ones of northern Germany. (The part of the Continent nearest to the Orkney Isles is really Norway, but the Common Vole is not found here. The Guernsey Vole, conversely, shows more similarities with the voles of Germany.) Almost certainly it was introduced to Orkney by Neolithic Man, as evidence found at Skara Brae and other Neolithic sites suggests.
Head/body length: 114 mm (range 90-135 mm); tail: 38 mm (range 27-45 mm). The tail constitutes about 30% of the overall head/body length. Body weight: 14-67g. The wide disparity in the weight is due to differences in age and sex, with males being approximately 10g. heavier than females.
The Orkneys comprise a group of over 70 islands off the north-east coast of Scotland, separated from the mainland by the stormy waters of the Pentland Firth, a channel up to 13 km (8 miles) wide and 55-74 m (180-240 ft) deep. Voles are present on all the larger islands except Hoy and Shapinsay. It is possible to tell from which island each animal originates by the colour of its coat. Those from the three southerly islands of Mainland Orkney, South Ronaldsay and Rousay, have a deep brown coat, whereas those hailing from the two northerly islands of Sanday and Westray are paler in colour. The Westray voles are also smaller for some reason. It is unlikely that captive specimens are pure-bred but probably have their provenances on several different islands.
There are no mammalian carnivores found wild in Orkney except for feral cats but a number of avian predators are present, including Buzzards (Buteo buteo) , Hen Harriers (Circus cyaneus) , Kestrels (Falco tinnunculus) , and Short-eared Owls (Asio flammeus) , amongst others.
Owing to shallow soils and the gales that regularly whip the islands, the low-lying Orkneys are virtually treeless. Where inclines do exist, some voles are found at elevations of up to 700 feet, although on the whole they prefer lower ground. Soils here do contain some peat but many are naturally lime-rich and most are continually being enriched from lime-rich seashore sands. Although lying nearly as far north as Greenland, the climate on the islands is surprisingly mild for most of the year on account of the North Atlantic drift current in the ocean. The average annual temperature is a relatively balmy 45° F. and the rainfall averages a mere 35 inches per annum, with most falling as a fine drizzle. There is a long summer photoperiod due to the northern latitude, a considerable assistance to the voles' breeding season.
The vegetation cover in the Orkneys is better than in the Shetland Isles because the local rock, mostly Old Red Sandstone, weathers down easily to form good quality soil, ideal for agriculture which, not surprisingly, has been the mainstay of the islands' economy since prehistory. This species prefers man-made environments. It favours cultivated grasslands such as fields, meadows and pastures, being especially fond of clover fields, but is also found in ditches, embankments, hedgerows, marshes, moors, and gardens.
In years of overpopulation the species spreads along man-made arteries, such as paths and railway lines, to colonise new areas.
One of the most peaceable members of the genus Microtus, Orkney Voles are capable of living in large colonies without showing any aggression towards fellow members, even though the species cannot be said to be truly social. I have many years' experience of keeping Orkney Voles, but cannot recall any instance of an animal being attacked by another. In this important respect they differ from many other species of vole which will live in colonies of hundreds of individuals but are strangely unco-operative and aggressive towards each other. In its natural habitat the population density depends on a number of factors, including fecundity, social spacing, amount of vegetation cover, and level of predation.
Active all year-round and does not hibernate. The Orkney Vole is both crepuscular and nocturnal in its habits, but, even in its natural habitat, is occasionally prone to short bursts of activity throughout the day. Conditioned captive specimens are often active on dull days. There is a 2-3 hour cycle of resting and foraging, with longer and more frequent resting periods during daylight hours. Slow-moving most of the time (unlike, say, the Bank Vole) and therefore quite easily trapped, it can nonetheless run quickly when the needs arises, its belly almost in contact with the ground, but with many frequent pauses. Stands erect on its hind legs to scan surroundings for possible danger. A behaviour that admittedly I have not seen performed by captive specimens.
Hardly ever jumps or climbs but an able swimmer and even capable of short dives. Orkney Voles rely on a network of conspicuous surface runways, especially visible through heather, that connect up a number of burrows just beneath the surface. The tunnels are often quite short, about 6 cm in diameter, terminating in nest-chambers and food larders. In winter the voles build nests of dry grass just below the snow cover. The home range is about 1000 square metres or less. Mostly silent but, when upset, angry or frightened, emits a high-pitched squeak, like a bird chirp, usually uttered just once but occasionally repeated several times, even as a continuous vibration and, if extremely agitated, will also gnash its teeth. In an exposed location, it follows this up by "freezing", so as not to draw attention to itself in the hope that the danger will pass, but usually if there is any sort of cover in the vicinity it just flees.
A mature adult male can be distinguished by his larger body size and the presence of an obvious scrotal sac. He is heavier than the female and possesses a scent gland on his rump. The ano-genital distance is approximately twice as wide in the male. Females possess eight mammae, but these are not obvious except very occasionally when the female is nursing.
A large glass tank with a secure, well-ventilated lid is best. If the ventilation is inadequate, unacceptable amounts of condensation will collect on the inside of the glass. Since this species spends so much of its time burrowing, it seems unfair to deny it this basic activity, and a deep layer of wood-chips or peat substitute should be provided. In this environment it is usually futile to try to provide "toys" and other furnishings because they soon get submerged. It is always a good idea to place some plastic or earthenware pipes and cardboard tubes in the tank, as well as a few twigs and branches for gnawing, and a wooden nest box (a budgerigar nest box is ideal) filled with a liberal quantity of dry hay.
In the wild, Orkney Voles eat the leaves, stems and roots of a wide range of grasses, sedges and herbaceous plants, as well as (when available) berries, bulbs, fungi, lichens, nuts, seeds, tubers (an excellent source of moisture), and even twigs and bark when other foods are scarce. Surplus food is stored for winter use. When the population is high, voles occasionally become a crop pest due to their penchant for grain and hay. They are particularly fond of the thick roots of the Heath Rush (Juncus squarrosus) , known locally as Moss Rush or Goose-corn, a common plant of acid moors and barren sandy or peaty heaths and drier situations than most of the Rush family.
Voles in general are strictly vegetarian, but have been known to take small insects occasionally. I know of at least one breeder who regularly offers his voles meal-worms, which they appear to relish.
In its natural habitat Orkney Voles have been known to consume their own weight in food each day. Their coarse herbivorous diet comprises cellulosic food which is difficult for any animal smaller than an elephant to digest and yields little of any nutritional value, forcing them to eat a lot in order to derive any benefit from the diet. Grass, though indispensable in the diet, is tough and difficult to digest and the cells are protected by a layer of silica, and consequently it passes through the digestive tract too quickly. In captivity, where the food is more concentrated and the animals are less active, their propensity to overeat can, if one is not vigilant, lead to their becoming overweight.
My colony receives a fairly bland diet of a good quality rodent mixture (one that is low in peanuts, sunflower seeds and other highly fattening items). To this I add fresh grass (complete with roots if possible), meadow hay, and a few pieces of chopped apple or carrots, fresh greens, or other raw vegetables or fruits. They can also be given rodent pellet, canary seed, rolled or whole oats, and canned or dry dog food. Wood gnaws are essential, as they are with all rodents. I feed them just once a day. I always pull the grass from my own garden where I know it to be uncontaminated by chemical sprays, car exhaust fumes, or dog urine. Never collect from the side of the road or other areas where the quality of the grass cannot be guaranteed, and do not use grass trimmings that have passed through a mower because of the danger of the trimmings being tainted with oil. They are the only species of vole I keep to which I regularly give apple, as they have always received it and have suffered no ill effects. Second only to the grass, it is the food item to which they are most partial.
Voles succumb very quickly if deprived of water for even a short while. It is usually no good attempting to provide water in an open dish; because of the voles' constant burrowing activities, they will soon deposit wood shavings or peat into the water, which will leak out due to capillary action and saturate the substrate. This is disastrous because voles cannot tolerate damp conditions for long. Even placing the bowl on a brick to keep it clear of the substrate proves effective only for so long. The best solution is to use a plastic or glass drinking bottle (the latter are superior but are getting increasingly difficult to find).
No mammal is known to be more prolific than the 65 or so species of meadow voles of the genus Microtus, and, not surprisingly, the Orkney Vole breeds freely in captivity. They are polyoestrus. There is a postpartum oestrus. Orkney Voles give birth 3-7 times per year from April to September, although some limited breeding is not unknown as early as February if the weather is mild and food is plentiful. Generally, however, reproduction is governed by day length. The optimum day length appears to be 12-14 hours. In a recent study, females kept under a regime of 12 hours of light and 12 hours of darkness took 42 days to mature, while those kept under 14 hours of light and just 10 hours of darkness matured in just 17 days. Voles kept in dimly lit cages do not seem to breed as prolifically as those kept in well lit cages. Originally I had two separate colonies. The smaller colony, consisting of 4-6 animals, lived in a large glass tank with no additional lighting. In this environment the voles bred, but not regularly and never predictably. The larger colony, on the other hand, consisting of up to 20 individuals, lived in a much smaller enclosure but with a fluorescent tube in the lid that provided bright light for 10˝ hours a day, lulling them into thinking it was high summer all year round. This colony bred prolifically and it seemed as if there were almost young animals in the nest. The nest consists of a rounded chamber of grass and roots is built slightly above or a little way below ground level. Litter size varies from 3-6, but in exceptional cases can be as many as 10. Litter size peaks in May. Orkney Voles are very prolific and numbers can increase rapidly under favourable conditions to reach almost plague proportions in some years. Females increase energy consumption by up to 250% when nursing young. Birth weight is 2 g. Eyes open at 9 days, and the young are weaned at 12-21 days. Sexual maturity is attained at around 25 days for females; and 45 days for males.
It is rare that the hand-rearing of offspring needs to be contemplated, as the mother is usually very good at rearing the young by herself. If, however, a nursing female should die before the young are weaned, it is worth remembering that a different but related species, the American Meadow Vole (Microtus pennsylvanicus) , was successfully reared using Esbilac®. On average they live about 1 - 1.5 years, although under optimum conditions in captivity they do occasionally live longer.
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