MEADOW VOLES (Microtus californicus)


Sign and damage Control methods
• Runways and open burrow entrances
• Presence of scats
• Girdling of vines/trees above ground
• Row and field crop losses from feeding		 • Vine/tree guards
• Toxic baits (zinc phosphide, anticoagulants)
• Cover crop selection and management
• Harbourage removal or modification


BIOLOGY
Meadow voles, also called meadow mice or field mice are small rodents with stocky bodies, short legs, and short tails. Their eyes are small and their ears partly hidden. Voles are active during the day and night, year-round. They construct shallow burrow systems with numerous entrances.

Under optimal conditions voles may breed throughout the year, but the breeding period is most commonly in spring and summer. In the field, they generally have up to 5 litters per year, but laboratory studies have shown that they are capable of producing up to 17 litters per year. Litter size may be as high as 11, but the average is usually 3 to 6. The gestation period is about 21 days, young are weaned by the time they are 21 days old, and females mature in about 35 to 40 days.

These reproductive characteristics enable vole populations to increase in size in a relatively short time, given favorable conditions. Consequently, large population fluctuations are characteristic of voles. Population levels generally peak every 2 to 5 years; however, these cycles are not predictable.
DAMAGE
Voles cause extensive damage to trees, vines, row crops and field crops. They girdle trees and vines at ground level. Vole girdling can be distinguished from that caused by other animals by the non-unigorm gnaw marks. They occur at various angles and in irregular patches. Marks are about 1/8-in wide, 3/8-in long, and 1/16-in or more deep. Rabbit gnaw marks are longer and not distinct.

Damage to artichokes


Extensive girdling damage to a young oak tree.

Ground vegetation, by providing food, concealment from predators, and protection from unfavorable weather is the most important factor affecting meadow vole abundance. Where cover crops are planted, vole populations are almost certainly favored, and without careful management, damage may be severe enough to kill many vines or trees, especially in young plantings.

Cover crop selection and management
• Species selection (erect bunch-type growth, avoid high moisture plants)
• Maintenance of a cover-free strip around bases of vines/trees
• Mowing to reduce cover and to facilitate detection of burrows

Cover crop management should reduce protective cover and eliminate contact between the vines/trees and the cover crop or clippings. Practices that reduce cover in surrounding areas can also play a role in preventing serious vole problems, because these areas often provide habitat for voles. These practices include controlling weeds; cultivating fencerows, roadsides and ditchbanks; and reducing ground cover in areas adjacent to vines.

Species selection -- Growth form is probably the most important consideration in selecting ground cover plants that are unfavorable to voles. Dense covers that form a continuous canopy support high vole populations. By contrast, plants with erect bunch-type growth that reach a short mature height require less mowing and increase the light penetration at ground level, thus providing voles with little protective cover.

Food preferences of voles should also be considered when selecting a cover crop. Voles prefer foods that have a high water or calorie content, or have nutrients such as nitrogen, calcium, phosphorous, and sodium. The planting of legumes and grasses that have a high moisture content should therefore be avoided if vole problems are likely.

Cultivation – Vegetative cover should not be allowed to directly contact vines or trees. Keeping the vegetation clear discourages voles from living near and causing damage to the bases of vines or trees. Where vole problems are severe, summer disking or mowing of the vegetation in the row middles also should be considered. If vole numbers increase substantially, clean-culture cultivation and plowing, along with lethal control measures, may be the only way to eliminate the problem.

Cover reduction – Frequent close mowing of ground cover (when possible) removes protective cover for voles and allows for detection of their presence. Mowing may also have a short-term impact by disturbing vole populations, causing individuals to disperse. It is important to note however, that clippings left as a dense thatch layer on the ground are likely to improve the suitability of the habitat to voles by affording them more protection.