Adorable but Devastating: Vanquishing the Vexatious Voles

Adorable but Devastating: Vanquishing the Vexatious Voles

Everyone seems to know about the “mouse problem” on our farm. The signs of rodent damage can be seen everywhere, and it’s not uncommon to see a small blur of brown streaking from one bed to another. But what exactly do we know about our furry neighbors? I say not enough. In my time on the farm, I’ve seen perhaps just one true mouse. The real culprit is actually a species of vole (most likely Microtus californicus) a rodent which is somewhat similar to a mouse yet has some key differences in behavior. To minimize damage caused by them, we must learn how to identify our pests and better understand how they fill their niche in the ecosystem. 

    Voles have a different body shape from mice to suit their lifestyle. While mice are small, skinny and adept at climbing, voles are relatively large, fat, and have short limbs, tails and ears. Below I’ve constructed a diagram which should help with some key identifying characteristics. Adult female voles are smaller than adult males. 

    The most telltale sign of vole presence is the extensive system of ‘runways’ they produce. Voles spend much of their time in shallow burrows, but also construct worn networks near or above the surface, often through vegetation or mulch, that they utilize to get from place to place. The burrows and runways both pose serious threat to crop yield as the voles disturb the soil and remove vegetation to create them. Burrows can expose crops’ roots to air and cause dehydration; they can also cause the entire plant to collapse and die from lost soil structure. Voles line the insides of their burrows with vegetation that they gnaw down, so even calorie-poor crops like  young rye and vetch aren’t safe from damage. I personally had most of my group's rye patch destroyed by voles; first they displaced the plants by constructing a runway through the middle of it, then they gnawed all the stalks down to line their burrows, and finally they dug out a burrow underneath it and caused half of the rootstock to collapse and die.

In addition to these secondary effects, voles directly consume almost any plant matter. They will relish root crops like beets and potatoes, but will also consume many other plants like cabbage, broccoli, artichoke, lettuce and brussel sprouts. They will also gnaw on the bark around the trunk of young fruit trees and can cause permanent damage or death.

    The fluctuating nature and fertility of wild vole populations makes them a top priority pest. Females become sexually mature at just a month of old and can give birth to about a dozen litters of 3-6 offspring in its year-long lifetime (Hatfield, 1935). In the wild, vole populations commonly fluctuate and can explode exponentially under ideal conditions until the number of individuals can reach plague proportions. Our farm does provide optimal habitat for them, so the risk of this happening shouldn’t be ignored. Although the population would decline on its own, the damage caused to our crops from the ravenous voles would be extensive to say the least. We must continue to keep a close eye on the number of voles implement population control methods when needed.

    Voles are active at all times of day and night, though they their activity has a correlation to the weather. During the heat of summer, they’re more active during the night, and in the middle of winter they come out during the day. They are also more prone to venture into the open during the evening, night and dawn. They don’t hibernate but tend to have fewer pups in the wintertime. Because they’re always active, we can attempt to catch them year-round during all times of day.

    Voles love to live in and around very dense plant and weed growth. Unfortunately for us, most traditional vole control strategies involve reducing or removing this cover. Since this isn’t an option we must use other methods. One of our most effective ways of controlling vole populations are the use of live traps. Since I began using these traps during winter break, I’ve relocated about twenty individuals from our farm to surrounding areas. Traps are best set up in close proximity to a burrow entrance or runway and near some cover, like a tall plant or some logs. This will help the voles to feel more secure and encourage them to go into the trap. The best bait I’ve found is some white bread with peanut butter smeared on it. I smush the bread into a dense ball so it stays together, then tie it to the trigger mechanism with some cotton string or a blade of grass. Most food items will work, but smelly foods which won’t fall apart are best. 

    Maintaining these traps is a big commitment since you must check the traps once or twice every single day, first thing in the morning. If they’re not checked, a mouse or vole will quickly die. We’ve also had reports of small birds (dark-eyed juncos) becoming trapped inside. It seems that my own as well as other students’ first instinct to re-set a trap that appears to have been sprung with nothing inside of it. To avoid miscommunication and potential incidence of death, we should agree to not set a trap unless you plan on checking it the following day, and to store traps not in use far away from the beds. Catching voles by hand can also work, but it is very limited in its ability to make a real dent in the population since there are only a few structures under which you can unreliably find rodents. 

Vole caught in a live trap

    In addition to direct intervention, efforts can be taken to increase natural predation on rodents. Local red-shouldered hawks and white-tailed kites both relish voles, as do night-hunting owl species. Building an owl box and a raptor perch nearby the farm may help keep the population in check. Gopher snakes, garter snakes and western racers are also natural predators, and all have been sighted in the surrounding areas before. Perhaps the racer from last semester will return this spring to lend us a hand. 

workers constructing a raptor perch

Despite all the destruction they caused, voles are actually a positive indicator species. This doesn’t mean that we want them on the farm, but their presence does indicate that we produce enough food on the farm to support their population. Several years ago when our site was just a field of grass, no vole could have survived long term due to lack of food and habitat.

-Jeremy Morrell