Minnesotans note a new neighbor: the Virginia opossumby Jeff Jones, Minnesota Public Radio
Minnesota Public Radio's Public Insight Network is asking Minnesotans to tell us what changes they're seeing in the natural world around them. We will be exploring the facts around these changes and what they mean for our region in an ongoing series of stories. Contribute your observations here.
Brent Olson has lived on a farm in western Minnesota for over 50 years, but for the first 40, he never saw an opossum. Now, the animals are common around his Otter Tail County property and throughout southern, western and central Minnesota...and they're moving north.
Olson is one of dozens of sources in MPR's Public Insight Network weighing in about changes they're witnessing in the natural world around them, from bird songs to lake levels, and he's one of several to report the arrival of opossum as a sign that things are changing.
Nika Davies also started noticing the opossum near her Apple Valley home in the last few years. "There were none when I moved here in 1986," she says. "I suspect more are thriving because of the milder winters."
Davies is right that average winter temperatures in our region have trended sharply upwards since 1980 (after trending slowly downwards for decades before that). But are milder temperatures really the reason opossum are moving north? Answering that question reveals a more complicated picture of how humans are influencing the natural world.
One of the people looking closely at Minnesota's new opossum residents is DNR biologist John Erb. He specializes in the group of small mammals known as "furbearers" and he says opossum (properly called "Virginia opossum") have been in far southern Minnesota for about 100 years, but their spread into the metro area and central Minnesota is quite recent.
"For somebody who's living in the Twin Cities or St. Cloud or other areas, possums are very new. But now at least a few individuals have moved past that line and so folks in Brainerd, and even Grand Rapids, Bemidji and Duluth, may stumble upon a possum," Erb said.
And opossum aren't the only critters new to our region. Grey fox and bobcats are also showing up in areas they were never seen before. But according to Erb, climatic changes aren't nearly as important to their arrival as physical ones.
The roads, bridges, ditches and culverts humans have added to the landscape in the last 200 years all make it easier for wandering animals to cover more ground. Farm fields may be easier to travel and scavenge in than forests or prairie were. And some creatures even hitch rides.
Jody Rooney of Hugo noticed opossum in the north metro in the mid 1990s. "The mythology was that possums came up in big round hay bales when we had a drought," she said. The bales were imported from Missouri and Iowa, where opossum have long been common. John Erb can't confirm that itinerary, but he's certain that type of movement occurs among small mammals. "Not just hay bales of course, but you have semi [trucks] that are being loaded in an alley someplace to the south and an opossum gets in the semi and they drive to Duluth to unload," he said. "The movement of animals no doubt occurs in those manners."
But while many inventive animals could hitch a ride to Duluth, most newcomers can't survive the Minnesota winter. Warmer temperatures may indeed be helping the handful of opossum pioneers tough out the cold weather, but biologists point again to human activity as a more important factor. They say man-made structures like barns, cabins, porches, and even hay bales make it easier for small animals to find a place to wait out the cold conditions -- even in an unusually harsh winter like this one.
"We do commonly see them with their ears frozen off and tail tips frozen off," Erb said. "So it still is affecting some, but they're apparently finding enough [shelter] to slowly move their way north."
So what effect will these new arrivals have on Minnesota? Biologists say opossum don't really compete for food or territory with other animals and they're not forcing other creatures out. They also aren't known to significantly harm crops or spread disease...with one exception.
Jody Rooney of Hugo is an avid horse-rider and she remembers the arrival of opossum in the 1990s setting off alarm bells through the horse community. That's because opossum carry a disease that can cause a neurological condition in horses called Equine Protozoal Myeloencephalitis.
"The more possums you have, the more likely you are to have horses exposed," says Stephanie Valberg, Director of the Equine Center at the University of Minnesota's college of veterinary medicine. The condition is only harmful to horses and is spread when horses eat food that's been in contact with opossum feces. But Valberg says the latest research shows most exposed horses never exhibit symptoms of the disease and those that do probably have comprised immune systems to begin with.
The DNR's John Erb says the main effect opossum will have on our region is that people will simply have more animals to look at -- and hunt. Opossum, like badgers, can be hunted from late October to mid-March without limits.
What changes are you seeing in our region's changing natural landscape? Please let us know by answering our short query and joining the Public Insight Network. A reporter may contact you to find out more.
- All Things Considered, 03/09/2011, 5:48 p.m.