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A gnawing problem: 'Mouse madness' might strike the Lakes Area again...or it might not

Experts say it could be another bad year for mice in the Lakes Area, thanks to an early spring -- but that's only if a number of other factors come into play to create another 'perfect storm' like last year. File photo

Will this year bring another invasion of the cheese snatchers?

After suffering through what one news story called "mouse madness" last summer and fall, a lot of Lakes Area homeowners are wondering what rodent-related headaches the season ahead might bring.

Answers from experts basically amount to a leery "we'll see..."—a discouraging message for those hoping to avoid, or at least prepare for, another big influx of outdoor mice.

Last season's population of deer mice seemed to explode, especially toward the end of fall, and people from all over the Otter Tail and Becker county areas were reporting much higher-than-usual mouse sightings in and around their homes, garages, vehicles, sheds, etc.

Residents reported catching upwards of 75 mice inside their houses over late summer/early fall, while pest control companies were booked up with rodent control jobs, hardware stores had to order extra traps and poisons to keep shelves stocked, and pet adoption facilities noticed an increased demand for cats.

There was plenty of speculation about why the mice were so bad. The most popular theory was that the previous winter's warm weather was too easy on them, allowing for higher-than-usual survival and reproduction rates. Then, a failed acorn crop drove a lot of those mice into people's homes to find food.

Dr. Joseph Whittaker, an assistant professor of biology at Concordia College in Moorhead, believes that theory is plausible. However, he's quick to caution that mouse populations are a complicated science, and he said no one really knows for sure why numbers spiked so high last fall.

"I'm not really sure what caused the explosion last year," he said. "When things line up perfectly, you get a big mouse population, but when they don't, you don't... There's a lot of research on it, but there's not a lot of consistency in the research."

Whittaker explained that there are multiple interwoven factors that play into the peaks and valleys of small mammal populations, and researchers are still trying to understand how those interactive features work together.

For example, this past winter was another mild one, but that doesn't necessarily mean there'll be another big influx of mice this coming summer and fall. If there were a lot of predators around over the winter, or if food was scarce, then only a small number of mice may have survived, despite the mild weather. Also, even if the mice do get bad again, people may not notice so much this time around. This year's acorn crop and other outdoor food sources could be abundant enough to sustain the mice, so they won't be driven indoors to eat.

Because weather, food supply, predator populations and other factors are so variable throughout every season, Whittaker said, it's nearly impossible to make accurate predictions about mouse populations.

Don Schultz, a wildlife supervisor with the Minnesota Department of Natural Resources out of Fergus Falls, shared that sentiment.

"Nobody knows what the mouse population is going to be like this year," Schultz said. "Rodent populations tend to be cyclic, so it's anybody's guess... There's only speculation about why it seemed to be so high last year."

Leading up to last year's big boom, Whittaker and a team of other researchers from Concordia saw no signs of the impending "invasion." The group does some small mammal trapping around the Lakes Area every year to monitor population changes, he said. Last spring and mid-summer, they were catching their usual number of mice—just a few out of a total 50 traps set. It seemed like an ordinary season.

But when they went back out again in the fall, 49 of the 50 traps were full.

"You usually expect about a 10 percent return on mouse catching, so to see an almost 100 percent return is almost unheard of," he said.

That's why this year, even though he's seen no signs of a higher-than-usual mouse population so far, he can't say with any certainty that the situation won't change, perhaps even drastically, by fall.

Whittaker said a colleague of his who researches wild birds has found one to three dead mice in almost every nest box this spring. That suggests that there was a "very high overwinter mortality" of mice, he explained, and that could be a sign that the population won't be as strong this spring.

On the other hand, because spring started early, "the other situation could be that it's so warm now that the plants are getting a jumpstart, and so the mice may be getting a jumpstart, too," he said. "So it may just be that we get another explosion."

Deer mice typically reproduce about every three to four weeks, so a longer warm season gives the females time to have one or even two extra litters before winter comes.

"I've already caught one this year that was pregnant," Whittaker said. "They can have seven to nine babies in a litter, so if spring starts early enough...that's going to have an explosive impact on that population."


-Start with some online research. There are all kinds of tips and tricks on the internet about how to rid your home of mice safely and humanely, or about where and how to set traps. You can also read up on how to prevent mice from getting into your home in the first place.

-Seal up any visible openings into your home. Check your window screens for holes (mice can get through a hole the size of a dime) and make sure the bottoms of your doors are right up against the floor, as mice can squeeze through very slim cracks. Also seal around any pipes coming in and out of your home.

-Keep lids on all your garbage and recycling bins, as food smells will attract mice.

-Keep things clean. Get rid of brush piles or other places around your yard where mice might like to hide, and keep the inside of the house tidy. Don't leave food sitting out for long, and clean up crumbs after every meal.

-Set traps. Live traps are a humane way to get rid of mice, though snap traps are widely considered to be the most effective way. Glue traps and homemade water traps are other options. Place them in areas where you've seen signs of mice (droppings or nests), and bait them with something aromatic, like cheese or peanut butter. Traps should be checked frequently and any dead mice disposed of promptly inside a tightly sealed plastic bag. The smell of mice can attract more mice.

-If you choose to use poisons, use them with caution. Poisons meant to kill rodents can have unintended consequences for family pets, children and even other wildlife in the area. Slower-working poisons take days or weeks to kill mice, and can harm or even kill birds, foxes and other predatory animals that eat those mice in the meantime. Faster-working poisons present a serious risk to pets and children that get a hold of them, as owners, parents and healthcare workers are afforded very little time to diagnose and treat the poisoning. Even when carefully applied to protected areas, poisons can be spread to other parts of a yard or home by rodents and insects.

-Encourage the presence of natural predators. Create roosting and nesting sites for owls and other birds of prey that feast on mice, and, if you live in a windy, open area, create a treed, protected spot near your home to attract and shelter larger wildlife.

Tips from Dr. Joseph Whittaker, previous Perham Focus stories and various online sources

Marie Johnson

Marie Johnson joined the Detroit Lakes Tribune in November 2017 after several years of writing and editing at the Perham Focus. She lives in rural Frazee with her husband, Dan, their young son and daughter, and their yellow Lab.

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