Harsh winter taking toll on Minnesota wildlife
White-tailed deer have retreated to the conifers. Mangy wolves near Grand Marais, Minn. are stealing suet balls put out for birds in residential neighborhoods. Snow is piling up thigh-deep in some parts of the Northland.
It's a real northern Minnesota winter.
The latest Winter Severity Index readings are out from the Minnesota Department of Natural Resources, and they're climbing fast. Those readings accrue a point for each day with below-zero temperatures and for each day with snow depths of more than 15 inches.
Understand, this winter is not approaching the big snow-and-cold winters of 1995-1996 and 1996-1997. And much depends on how long the cold and deep snows last. But Tom Rusch, DNR wildlife manager at Tower, thinks the winter could have an impact on deer.
"I think they're in for a long haul. I really do, unless this breaks," Rusch said. "We're getting reports already of mortality. Wolves are definitely going to have the advantage in winters like this."
DNR research biologists have learned that snow is the more significant factor in the WSI matrix, especially when it comes to effects on the deer herd. And it's deep.
Rusch reported snow depths of 37 inches on the Gunflint Trail, 31 inches near Orr and 22 to 30 inches in the Tower area last week.
WSI readings were at 89 on the Gunflint Trail as of Jan. 23, compared to 29 last year at the same time. At International Falls, the figures were 58 this year, 35 last year; Eveleth, 67 and 17; Tower, 61 and 29.
Even the wolves may be struggling a bit. Darin Fagerman, a DNR conservation officer at Grand Marais, said in his weekly report that he's "receiving calls on mangy wolves picking off low-hanging suet balls on bird feeders. One mangy wolf was on a deck sleeping against a house door. (Fagerman) tracked it on snowshoes, but couldn't get close enough to locate it. Some of the wolves in the worst shape will probably struggle for survival during the frigid temps we are now experiencing."
The situation is quite different in Wisconsin, said Fred Strand, where snow depths remain mostly below the state's 18-inch threshold for WSI points.
"So far, it's been a pretty decent winter for deer," Strand said. "Snow did come early -- mid-November -- and snow is the bigger factor in causing deer stress. . But snow, for the most part, has not been deep enough to inhibit their movement."
Current WSI figures weren't available from Wisconsin, but few areas have snow deeper than 18 inches, Strand said.
In northern Minnesota, deer have changed their patterns to deal with the deep snow, Rusch said. He has been up in an airplane recently for the DNR's annual moose census, and he can see where deer are as well.
"One of the things I've seen being up above is that the deer have vacated huge parts of their normal winter range and are in very tight thermal covers," Rusch said. "The cut-overs are vacant."
Deer move to areas of balsam fir and spruce that provide a micro-climate more favorable to their survival.
"It intercepts some of that snow," Rusch said. "Often there will be 6 to 12 inches less snow under that really good conifer cover. That makes establishing and maintaining trails easier, and avoiding predators. You can see their beds on the south and west sides of the trees. They kind of hunker down."
Hunters are watching and waiting to see how deer will endure the winter, said Mark Johnson, executive director of the Minnesota Deer Hunter's Association.
"I think across the state, people have been concerned about the deer herd," Johnson said. "From a severity standpoint, it depends on what happens from here on out."
The metabolism of deer slows during winter months, meaning they don't require as much food and therefore don't have to move so much seeking it.
Some deer always die in more difficult winters.
"This year's fawns, the 6-month-old deer, are the most vulnerable," Rusch said. "Back in 2009, I ended up with 23 deer I found killed by winter or wolves. Eighteen of them were fawns."
Adult bucks are next most vulnerable. Adult does are the least vulnerable to winter's bite.
Minnesota's moose are faring well despite the deep snow, Rusch said. With long legs, they're better adapted to that. But their calves are sticking close to their mothers, he said, letting the adults break trail.
Ruffed grouse seem to be doing well, both Rusch and Strand said. The snow cover is soft enough to allow grouse to penetrate into it, where they roost for much of each day. They conserve energy and avoid predators in that way.