Friday, December 9, 2022
HomePasture HealthForageOur Latest Plague: Meadow Voles

Our Latest Plague: Meadow Voles

I try to keep in touch with our custom grazing clients, maybe call them once a month or so during the winter months. This helps remind me to pay attention to forage conditions here on the ranch and lets them know that I’m thinking about them. Often, these calls include some personal conversations or potential troubles. Recently, I called Tom to tell him about some bad business bubbling up across my side of the State. His response made me think of the Bible.

“Well, what is this time? Fire? Flood? Locusts? Plague?”

“Nope. Voles.”

“What the heck is that?”

Meadow voles can grow to about 6 inches long (with a 2.5 inch tail) and usually weigh about 1.5 oz. They can swim, and use vocalizations and stamp their feet to protect themselves from predators and can become aggressive when trapped. The meadow vole consumes 60% of its body weight each day, eating grasses, sedges, seeds, tubers roots and the occasional insect. Under the cover of snow, the meadow vole may girdle trees and shrubs, consuming the inner bark. Breeding occurs year round. Females begin mating within 25 days of birth and have litters of 2 to 3, but sometimes as many as 9. With a gestation period of only 21 days, pastures can quickly be overrun by voles.

Actually, I’d received a couple of calls from friends over the past few months, telling me that they were very concerned about what seemed like a tidal wave of voles, entire fields covered by runways and burrows, all of the green disappearing from meadows and hay fields. Some folks were talking about the possibility of massive farming and re-seeding. This caused me to begin wandering around a bit, taking a more critical look at some of our pastures. Then I attended a Zoom meeting with my grazing group. When the topic of voles came up I mentioned that in some places I was seeing about one vole burrow per square foot. My pal Jon just laughed, telling the group that parts of his place were much worse than that. Shaken, I decided to take a closer look and visit several paddocks on each of our properties and see where we stood.

In Field Biology (no pun intended) we sample things on the ground by using a device called a quadrat. A quadrat has a known area and can be tossed randomly to capture a small survey. In this case, I intended to go out and toss my quadrat, count vole burrows, and calculate just how big the problem was. But as I began the project, it soon became clear that the nature of my project would make it very difficult.

Our grazing properties are very diverse: flat, steep, wet, dry, rocky, clay, loam, forest and swamp. As I wandered from place to place one thing became clear: the voles clearly preferred some places over others. They didn’t like the fields that were 100% saturated with ground water. What they really liked were fields that had suffered from heavy infestations of Tarweed and Queen Anne’s Lace (wild carrot) that I wrote about last summer. These paddocks were left covered with a “forest” of stiff, dead, brown weed stems. And the ground beneath those dead weeds was stripped bare of any green foliage. Burrows and rodent trails were everywhere. In terms of growing grass, I judged these paddocks to be…devastated.

Why are they choosing some sites over others? Perhaps it has to do with safety. Over the years I have noticed that the area directly beneath our single-wire fences always harbor large rodent populations. I assume this is because they are somewhat protected from raptor predators. It seems likely that this current phenomenon of voles populating the areas beneath the dead weed forests is related to the same thing: birds of prey do not like to dive into areas where they might be injured.

Ava, my bird dog, hunting voles. There are so many, she has given up eating them. Still, I notice my dog food bill has been markedly reduced this spring.

There are some things I really don’t know:

• What will these fields will look like in three months or six months?
• What effect will the voles have on total production on our different properties?

One thing I do know:

• The plant community on some of our paddocks looks terrible, and I worry about our carrying capacity this coming spring.

Later on, when I called Jon back to ask for his thoughts, the main question wasn’t about the current lack of forage, but about what was going on under the ground. Were the voles just harvesting foliage, or are they actually eating the roots and killing the plants? I’m not certain we have a good answer, but places look pretty scary.

At this point, I’m trying to remain positive but conservative. I have told my custom grazing clients that based on my observations I expect perhaps a 25 or 33 percent reduction in grazing this spring and summer. I will make that adjustment by working on plans to liquidate some of my own personal cattle as the grazing season unrolls. What is interesting about this approach is that it is exactly the same thing I would do in a drought: reduce stocking rate to accommodate a loss of growth and make those reductions before the rest of the ranching community recognizes the problem or floods the local market.

Hoping for the best, and also for happy grazing season here in the Calapooia valley.

John Marble
Crawfordsville, Oregon

Update:

This was written a couple weeks ago and John has continued to monitor the impacts of voles. He wrote me this week to say he’s updating his damage estimate to 50% loss of production. As he noted above, he’s now implementing the “vole” version of a drought management plan, reducing cattle numbers to match the remaining available forage.

John also talked about his management for voles being a lot like his drought management plan. If you don’t have one yet, download Drought Planning 101 from the Bonus Content provided for paying subscribers. Here’s what it includes:

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John Marble
John Marble
John Marble grew up on a terribly conventional ranch with a large family where each kid had their own tractor. Surviving that, he now owns a small grazing and marketing operation that focuses on producing value through managed grazing. He oversees a diverse ranching operation, renting and owning cattle and grasslands while managing timber, wildlife habitat and human relationships. His multi-species approach includes meat goats, pointing dogs and barn cats. He has a life-long interest in ecology, trying to understand how plants, animals, soils and humans fit together. John spends his late-night hours working on fiction, writing about worlds much less strange than this one.

4 COMMENTS

  1. Vole explosion years help keep my livestock guardian dog food bills down.

    I visited some friends who farm on an island in Lake Ontario. When we walked through their fields, you could see ripples in the grasses ahead of our feet, like the bow of a boat plying the water. If you stopped suddenly, you could hear them scurrying away from your path. (Or at least I could then; my ears aren’t what they were 20 years ago.)

    They had guard dogs that hadn’t touched their dog food for months.

    Coyotes, foxes, raptors, free-range chickens — everyone has a field day when meadow voles populations explode. These explosions seldom last long and they happen in fairly predictable cycles lasting 5 to 7 years. After these booms, there will be a crash when you don’t see a vole hardly at all and the dogs are all hungry all the time, and then the population will gradually build.

    The COVID-19 epidemic has familiarized us all with the exponential curve, and that’s basically what happens with voles. One year they skyrocket, but they reach a saturation point and diseases, starvation, or a harsh winter will wipe them out. If only viruses followed this latter part of the pattern!

    At least in the high rainfall areas of the East they don’t seem to have much impact on pasture productivity over the course of the season, though they may delay early grazing a bit.

  2. We have meadow voles in all pastures and hayfields. If in hayfields, the crows, ravens, kestrels and red-tailed hawks devastate them when we cut or rake. Foxes, coyotes, owls, and weasels do lots of hunting at dawn, dusk, night. Thank God for predators.

    When they reach plague proportions, farmers here tend to make sure there is not much cover in the fall (which may not be best for the grass). I think voles may breed under the snow but have not confirmed that.

    I have a series of photos of least weasel tracks hunting voles by running down a bare fenceline and then entering the snow beneath the crust where the fence posts have left a “hole” in the snow due to heat concentration on the posts.

    Like John’s dog, my dog(s)–over the years–have devoured zillions of voles in bad years. Probably should worm the dogs.

  3. Hi John,
    I think you may find the tansy and wild carrot patches are actually the product of previous vole damage. Our increasing Canada thistle infestation is almost entirely due to voles weakening our grass cover in those areas.
    On our irrigated pastures, we have see up to 40% reduction in grazing yields due to voles in heavily infested areas.
    We had one client near Twin Falls who had to completely reseed three pivots due to vole damage.

    On the positive side, I have seen over 1000 dead voles/acre after high stock density grazing. Cattle stomp a lot of them. If you see one dead vole on average per 6ft x 6ft area, that will equate to over 1000 dead/acre if uniformly distributed. You may see a half dozen stomped on one 6×6 quadrat and none in others.
    We frequently see hawks perched on the center pivots to prey on voles.
    A healthy coyote population will also make an impact on voles. Research shows a single coyote may eat 30-40 voles per day, especially in fall & winter.
    Jim Gerrish

    • Our old friend Mr.Occam advises that when someone has a hypothesis that is better than your own, you should steal it. Well, that’s kind of what he said. Anyway, thanks Jim, and I have to admit, your explanation for the Tar Weed and Queen Ann’s Lace invasion we suffered through last year makes good sense. I guess my biggest concern now (even if a plague wipes out the voles) is what the effect will be from massive amounts of bare ground associated with our current infestation. I’m not a fan of disturbance-farming, but I’m afraid I see tractors in my future. Aaargh.

      Thanks again, and by the way, I’m seeing more coyotes every day.
      🙂

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