More mice, more problems

By Linda Bell
Correspondent

Mickey and Minnie are cute, but it stops there for most rural residents. Disneyland this is not.

According to John Pape, an epidemiologist with the Colorado Department of Public Health and Environment, there was a substantial increase in deer mice this summer all over Colorado. This is not exactly news to most mountain residents of the northern Front Range, who are buying traps, poisons, steel wool and cats at record pace, while checking under car hoods and daily sweeping out their vehicles.

Patti McMillan, owner of the Red Feather Lakes Trading Post, said she's sold 48 boxes of D-Con a week since June, where in past summers it's usually less than 12 a week. Traps are also flying out the door, she added.

Pape and others credit the increase in vegetation after several years of drought for the sudden increase in mice. With adequate food, the critters easily survive, litters are large, and many more young quickly become mating adults, said Jim Jackson, district wildlife officer for Red Feather Lakes.

Jerry Craig, a raptor specialist and former researcher with the Colorado Division of Wildlife, said there also might be a serendipitous coincidence that last year's outbreak of West Nile might have suppressed numbers of some raptors, great horned owls, crows, ravens and magpies that all prey on rodents.

"That's just speculation," Craig said, "because we don't have bench mark numbers for common raptors, only uncommon species, so when their numbers drop, we don't know by what factor." An adult owl, he said, takes about a dozen mice per day.

Hantavirus precautions

The bad news is that deer mice carry hantavirus that can be transmitted to humans through mice excretions, Pape said. There has not been a case of hantavirus in Larimer County since 1999, but with mice populations up all over the state, people need to be aware of the possibility, he said.

"Hantavirus is a lot like lightning," he said, "rare but very dangerous."

Pape said the virus does not survive more than a few days in mouse excreta. "If it did, we'd see a lot more cases," he said.

Deer mice are two-toned with brown on the top and white underneath, including the tail. They have large ears relative to their head size. These are different than small gray house mice commonly found in urban areas, which are all gray, have small ears and don't carry the disease.

Pape listed four precautions people could take to limit their exposure to the virus: rodent proof the house and outbuildings to limit entry; get rid of habitat and easy food supplies like bird seed, dog food or grain; develop a year-round rodent control program to keep ahead of them; wear gloves and use a bleach-water spray to wet down any new nest material or excreta before disposing of it.

Control measures

Jackson said as cold temperatures set in, the problem will get a whole lot worse for rural residents as the mice start looking for warm places to spend the winter. But reproductive cycles should slow, so that's some good news, he added.

Brian Rutledge, a wildlife consultant and resident in the Cherokee Park area of Livermore, said he watches about 50 to 60 deer mice take shelter in his barn every night, and they ate his wife's briefcase inside her car one night. He noted the coyote population should be doing well, and most of the snakes he's seen have been healthy prairie rattlers - but there just aren't enough of them around areas of human disturbance.

Monica Gerson, a resident of Glacier View Meadows who commutes to Fort Collins daily, found her car wouldn't start recently. "When I popped the hood," she said, "it was full of seeds, dry grass, leaves and twigs forming nests. I'm amazed the car didn't catch fire on Highway 287."

She said the critters did $628 damage, eating through the cable that runs to the car's computer and the thick alternator wire, plus they ate anything made of rubber or plastic.

Red Feather Lakes mechanic Jim Beck said he sees about two cars a day that have been chewed or damaged by rodents.

Jackson said the best way to discourage rodents nesting in a vehicle motor is to leave the hood up a few inches, enough to break the seal around the top, and leaving a little wind and light to circulate under it. A person can do this in a garage easily enough, he said. If a vehicle is parked outside, however, owners should make sure the car isn't facing into the wind, or they should secure the hood with bungee cords to make certain it doesn't rip up.

Everyone seems to be into trapping, both live and dead, or relying on domestic pets to lend a hand. Jackson said live trapping followed by release will probably transfer the problem to someone else, or the critters may beat the trapper back to the house.

Jackson suggests the best way to dispose of trap-killed mice is to throw them back to nature, where other living creatures will recycle and benefit from them. Pape favors bagging them and putting them into the garbage.

Some people use live traps because they catch more mice at one time, but then have the problem of disposing of the catch. One Red Feather Lakes resident heard the best way to dispose of mice in a live trap is to submerge mice and trap in a solution of 1-to-10 bleach and water, which disinfects the trap at the same time. Another who live traps transfers the mice into a Ziploc bag that she puts into her deep freeze.

"One time though," she said, "they ate through the bag and took up residence in the freezer, so a week later when I went to get something out of it, there were all these eyes looking at me, quite alive and well fed!"

On the positive side, Rusty Enscore, an environmental health officer with CDC, said deer mice--the most common rural household invader--are unlikely to carry the kind of fleas that transmit plague to humans. He said fleas tend to be genus specific, and mice fleas don't bite humans. However, he said, when the body of the fleas' host goes cold, they look for another warm body, and that might be a domestic dog or cat. People should protect their pets with flea powders if active trapping is going on near them, he advised.