The voles are coming!
Regarding the great meadow-mouse boom of 2005 and its grisly remainder
“Geez, did you see that?”
“You almost hit it!”
“What was it? A gopher?”
“It wasn’t a gopher it was a … omigosh, there’s another one— look out!”
“Oh no. I think I got that one. I saw it in the rearview mirror.”
“What ARE those things?”
“They’re hamsters! … No, mice!”
“They’re really big ones.”
“Well, they’re not gophers. Gophers don’t have tails.”
“Yes they do, but they’re short.”
“Could they be lemmings?”
If you’ve had this conversation recently, then you’ve discovered that parts of rural Sacramento County recently have been overrun by epidemic numbers of rodents. Some stretches of road are ghoulishly paved with tiny, furry bodies with odd tails. The culprits aren’t gophers or rats or hamsters. They’re California voles: Microtus californicus, sometimes called “meadow mice.” They look vaguely like mice, but they have very short, furry ears and a short, furry tail. Voles are grazers and build extensive tunnel networks in dense grasslands while stockpiling little haystacks for food and bedding.
Closely related to lemmings, voles share the explosive population boom and bust cycles that characterize their famously (though not really deservedly) suicidal cousins. Voles can mature in as little as 21 days and produce five to 10 litters a year. With three to six young in each litter, it doesn’t take long to go from the usual 100 per acre to 5,000 per acre. This year, with a long, wet winter and abundant grass, the vole population has exploded in many grassland areas of the Central Valley. The results can be seen (sadly) on many country roads and on various farm crops. In mid- to late summer as the grass begins to dry, voles venture out from the dense grass to browse green vegetation and the bark of fruit trees. San Joaquin County Farm Adviser Mick Canevari says voles are a perennial problem in alfalfa. Hungry voles also gnaw artichokes, lettuce and tomatoes, and girdle young grapevines and walnut, almond and citrus trees.
Oddly, the epidemic is spotty. Gardeners in Galt and Lodi indicate these are the highest populations in several years, and the Cosumnes Reserve staff reports seeing huge numbers of voles. Grower Steve Viani, who farms near Pilot Hill, is putting tubes over his seedlings to hold off the hungry horde. At the same time, biologists from the California Department of Fish and Game report no significant increase in calls related to voles this year.
Voles are a “hub” species that supports a rich array of predators. Wherever voles are abundant, you can see red-tailed and Swainson’s hawks sitting along the fence lines, their crops so stuffed with mouse meat they can hardly fly.
American kestrels, which usually take large insects, can be seen laboring back to the nest, carrying fat voles to feed their young ones.
Great egrets can be seen prowling the edges of the alfalfa field and wolfing down little furry Snickers bars.
Coyotes and feral cats similarly come out to feast. And unseen, but just as dependent on this bounty, are the gopher snakes and rattlesnakes that will be exceptionally abundant the year after a big vole year.
This free lunch also has a devastating effect on the variety of roadkill. When one vole gets smushed on the road, it’s not long before another vole comes out to attend to his fallen cousin. Far from reading last rites, voles are opportunistic cannibals who enjoy a good mouse steak when no one is looking—and a second or third vole often joins the first. Should an owl swoop in to make an easy lunch of an injured vole on the road, he, too, may become part of the gruesome buffet.
Owls actually eat so many voles that many vineyards in Sacramento, Merced and Napa counties erect owl condominiums to entice them to move in. Voles do a lot of damage to grapes and other agricultural crops, but poisons and pesticides that might reduce vole populations have devastating effects on other non-targeted species. Enter the owl boxes. One pair of owls eats about 2,000 gophers, mice and voles a year. An owl couple also can produce eight to 25 young in a year. According to one study, a pair of owls and 48 nest boxes can equal more than 6 tons of rodents removed from a farmer’s field. Tom Huffman, who sells owl nest boxes, says demand this year is the third highest ever. You can see the owl boxes all over southern Sacramento County.
So, what are we to do about this epidemic? Voles are good for owls and other wildlife, but they are bad for crops. Should we try to avoid them on the road? Are they endangered?
California voles are not endangered, yet. But any species that depends on thousands of acres of open grasslands may be imperiled as that habitat becomes less common. As for avoiding them on the road, it would be unwise to risk life or serious damage to avoid a vole. Besides, these are “density dependent” organisms. That is an academic way of rationalizing that whether crushed by a car or eaten by a snake, a certain number of these prolific animals are going to die in order for the population to continue. We are to do nothing about the epidemic. Nothing but observe and appreciate the creatures around us and the diversity of wildlife that depends upon them.
“Oops. I think I hit that one.”
E.J. Koford is a writer and biologist living in Elk Grove.