Vole

For other uses, see Vole (disambiguation).

Vole
The bank vole lives in woodland areas in Europe and Asia.
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Cricetidae
Subfamily:	Arvicolinae in part
Genera
Arvicola Lagurus Microtus Myodes Phenacomys Pliomys

A vole is a small rodent resembling a mouse but with a stouter body, a shorter hairy tail, a slightly rounder head, smaller ears and eyes, and differently formed molars (high-crowned and with angular cusps instead of low-crowned and with rounded cusps). There are approximately 155 species of voles. They are sometimes known as meadow mice or field mice in North America. Vole species form the subfamily Arvicolinae with the lemmings and the muskrats.

Description

Voles are small rodents that grow to 4-8 inches depending on species. They can have 5-10 litters per year. Gestation lasts for 3 weeks and the young voles reach sexual maturity in a month. Needless to say, vole populations can rapidly grow from one or two to many within a very short period of time. Since litters average 5-10 young, a single pregnant vole in the yard can become 50 or more in less than a year.

Voles are commonly mistaken for other small animals. Moles, gophers, mice, rats and even shrews have similar characteristics and behavioral tendencies. Since voles will commonly use burrows with many exit holes, they can be mistaken for gophers or some kind of ground squirrel. Voles can create and will oftentimes utilize old abandoned mole tunnels thus confusing the land owner into thinking that moles are active. When voles find their way into the home, they are readily misidentified as mice or young rats. In fact, voles are unique and best described as being a little bit like all the other animals they are so commonly thought to be.

They will readily thrive on small plants. Like shrews they will eat dead animals and like mice or rats, they can live on most any nut or fruit. Additionally, voles will target plants more than most other small animals. It is here where their presence is mostly evident. Voles will readily "girdle" or eat the bark of small trees and ground cover much like a porcupine. This girdling can easily kill young plants and is not healthy for trees or other shrubs.

Voles love to eat succulent root systems and will burrow under plants or ground cover they are particularly fond of and eat away until the plant is dead. Bulbs in the ground are another favorite target for voles; their excellent burrowing and tunnelling gives them access to sensitive areas without clear or early warning. A vole problem is often only identifiable after they have destroyed a number of plants.

Controlling Voles (Meadow Mice)

Voles, also known as meadow mice, short-tailed mice, and orchard mice, can be serious pests of gardens, crops and orchards. Voles are often confused with house mice, and sometimes with moles and gophers.

Before getting too excited about how to eliminate voles, it is important to remember that voles are an essential link in the food chain, providing a major part of the diet for many predators, including coyotes, foxes, badgers, weasels, cats, gulls, and especially hawks and owls.1 It is important not to control them unless they are doing clearly unacceptable damage.

Voles are notorious for going through unpredictable population cycles that occasionally spin out of control. In parts of the Willamette Valley, vole populations in the winter of 2005/06 rocketed to up to an estimated one million voles per acre.2 That adds up to 20 voles per square foot, an astounding and clearly unsustainable number. The following summer, hardly a vole was to be found. This was likely due to a lack of food and the spread of disease, (or, possibly, a lack of enough space to lie down and go to sleep!)

Identification Voles are mouse-like rodents with compact, heavy bodies, short legs, short-furred tails, small eyes, and partially hidden ears.3 The long, coarse fur is grayish to blackish brown. When fully grown they can measure five to eight inches long, including the tail. Voles differ from house mice in that they are larger and have shorter tails and smaller ears.

Voles spend most of their time below ground in their burrow system but establish above-ground runways that connect burrow openings.4 These runways are usually hidden beneath a protective layer of grass or other ground cover. There are multiple burrow openings about 1 1/2 to 2 inches in diameter that lead to a tunnel system just below the ground surface that is used for feeding on plant roots. A deeper set of burrows, typically six to eight inches deep, are used for food storage, nesting, and rearing young.

Biology and Behavior Voles can begin breeding after only three weeks of age and produce four to six offspring per litter, with as many as ten litters per season.4 Species of voles that live at higher elevations have shorter breeding seasons. The gestation period is three weeks. Their life span is two to sixteen months. Voles are active day and night, year-round.5

Several adults and young may occupy a burrow system. Their home range is usually a few hundred square feet. Voles feed on a variety of grasses, herbaceous plants, bulbs, and tubers. They will also eat bark and tree roots, especially in fall or winter. Voles store seeds and other plant matter in underground chambers.

Damage Voles cause damage by their feeding, especially when numbers are high. Damage to tree trunks normally occurs in the area just above or below the ground surface, sometimes causing girdling that can kill trees. Where snow cover is present, damage to trees may extend a foot or more up the trunk, and may escape notice until it is too late.

Monitoring The distinctive on-the-surface runways, which may be partially hidden by grasses and weeds, and the small numerous burrow openings are the main signs of voles. On trees, gnaw marks about 1/8 inch wide and 3/8 inch long found in irregular patches may be found. Remember to check for below-ground damage by pulling soil away from tree trunks. In areas with winter snow, voles can do serious damage to tree trunks hidden under the snow pack.

Controlling Voles Vole control, especially on large acreages, can be a serious challenge. While total vole control may not be possible, you should be able to keep the numbers down to a level that is tolerable through a combination of pest control efforts.

Removing or Reducing -Vegetative Cover Heavy mulch and dense vegetative cover encourage voles by providing food and protection from predators and environmental stresses.6 Mowing and frequent soil cultivation helps to make areas unsuitable to voles.4 Where feasible, maintain weed-free buffer strips around gardens at least fifteen feet wide. A four-foot diameter vegetation-free circle around the base of young trees or vines can also reduce problems. Wood chips and paper mulches are not favored by voles. Nor is vetch, for those who want to use a winter ground cover.6

Vole Fences Because voles are poor climbers, wire fences at least twelve inches above the ground with a mesh size of 1/4 inch or less will help to exclude voles from gardens.4 These fences can either stand alone or be attached to the bottom of an existing fence. Bury the bottom edge of the fence six to ten inches to prevent voles from tunneling beneath it. A weed-free barrier on the outside of the fence will increase its effectiveness.

Potato farmers in eastern Oregon have used twelve inch aluminum roof flashing to make a short fence to enclose whole fields that was effective in keeping voles out.5 This was surrounded by a 30 foot buffer that was kept clean-cultivated.

Tree Guards Young trees, vines, and ornamentals can also be protected from girdling by putting cylinders made from hardware cloth, sheet metal, or heavy plastic around the trunk.3 Support or brace these devices so that they cannot be pushed over or pressed against the trunk. Also, make sure they are wide enough to allow for tree growth and, in areas with snow, are tall enough to extend above snow level. Be sure to check periodically to make sure voles have not gnawed through or dug under cylinders.

Trapping Using simple snap-type mouse traps is often effective, especially in smaller areas.4 Don't skimp on the number of traps you use. Use at least a dozen for small gardens, though more is better. Traps can be baited with a little peanut butter or used unbaited. A few oats can be placed next to the traps in the vole runways too.

Trap placement is the key. Voles seldom stray from their runways, so set traps along their routes. Place baited traps at right angles to the runways with the trigger end in the runway, or use them in pairs with the triggers facing out in opposite directions. Examine traps daily and remove dead voles or reset sprung traps as needed. Continue to trap in one location until no further voles are caught.

Be careful handling dead voles as they are known to host various serious diseases such as plague and Lyme disease, though there are no reports of voles as vectors of disease to humans.4 Nevertheless, to be safe, wear plastic or rubber gloves when handling dead voles.

Several Methods Not to Use Baits can cause secondary poisoning to predators that eat poisoned voles and kill non-target creatures such as birds. Commercial repellents have not been proven effective against voles.3 Nor are burrow fumigants effective due to the shallow burrow system with numerous open holes. Electromagnetic and ultrasonic devices are also considered ineffective.

Putting Voles into the Bigger Picture The narrow confines of this article portray voles mostly as pests. But, please remember the importance of voles in the ecosystem. Low population levels generally do no appreciable damage to human crops and gardens. Remember not to be in a hurry to kill them. Even last winter when populations skyrocketed, nature took care of bringing numbers back into control without the need for any human intervention.

Diet

Depending on the species, the vole's diet consists of seeds, tubers, conifer needles, bark, various green vegetation such as grass and clover, and insects. Some species will die, however, if deprived of their main meal, Douglas Fir needles, for too long.

Predators

Many predators such as martens, raccoons, owls, hawks, falcons, coyotes, foxes, snakes, the red tailed hawk, weasels, and cats eat voles. A common predator of voles is the short-eared owl as well as the northern spotted owl, the Saw-whet Owl, the barn Owl, and the Northern Pygmy Owl.

Lifespan

The average life of a vole is 3–6 months. Voles rarely live longer than 12 months. The longest lifespan of a vole ever recorded was 18 months.

Genetics and sexual behavior

The prairie vole is a notable animal model for its monogamous sexual fidelity, since the male is usually faithful to the female, and shares in the raising of pups. (The woodland vole is also usually monogamous.) Another species from the same genus, the meadow vole, has promiscuously mating males, and scientists have changed adult male meadow voles' behavior to resemble that of prairie voles in experiments in which a single gene was introduced into the brain via a virus.

The behavior is influenced by the number of repetitions of a particular string of microsatellite ("junk") DNA, and the same DNA sequence is found in humans. Male prairie voles with the longest DNA strings spend more time with their mates and pups than male prairie voles with shorter strings. However, other workers have disputed the gene's relationship to monogamy, and cast doubt on whether the human version plays an analogous role. Physiologically, pair-bonding behavior has been shown to be tied up with vasopressin, dopamine, and oxytocin, with the genetic influence apparently arising via the number receptors for these substances in the brain; the pair-bonding behavior has also been shown in experiments to be strongly modifiable by administering some of these substances directly.

Voles exhibit complex genetic structures with much variation, and appear to be evolving rapidly when compared with other vertebrates. For this reason, they can be useful to archaeologists for dating strata, in a method referred to as the "vole clock."

Voles have a number of unusual chromosomal traits. Species have been found with anywhere from 17-64 chromosomes, and in some species males and females have different chromosome numbers. Female voles have been found with chromosomes from both sexes, and in one species the sex chromosomes contain 20% of the genome. All of these variations result in very little physical aberration: most vole species are virtually indistinguishable.

Classification

• Order Rodentia
  • Superfamily Muroidea
    • Family Cricetidae
      • Subfamily Arvicolinae (in part)
        • Tribe Arvicolini
          • Genus Arvicola - water voles
          • Genus Blanfordimys - Afghan vole and Bucharian vole
          • Genus Chionomys - snow voles
          • Genus Lasiopodomys
          • Genus Lemmiscus - sagebrush vole
          • Genus Microtus - voles
          • Genus Neodon - mountain voles
          • Genus Phaiomys
          • Genus Proedromys - Duke of Bedford's vole
          • Genus Volemys
        • Tribe Ellobiusini - mole voles
          • Genus Ellobius - mole voles
        • Tribe Lagurini
          • Genus Lagurus - steppe vole
        • Tribe Myodini
          • Genus Alticola - voles from Central Asia
          • Genus Caryomys
          • Genus Eothenomys - voles from East Asia
          • Genus Hyperacrius - voles from Pakistan
          • Genus Myodes - red-backed voles
        • Tribe Pliomyini
          • Genus Dinaromys - voles from the Dinaric Alps
        • incertae sedis
          • Genus Arborimus - tree voles
          • Genus Phenacomys - heather voles

External links

• Voles.com, pictures and information about voles and vole related topics
• Pest control article
• National Geographic video.