Wild creatures employ survival strategies to adapt to long Minnesota winters

Old Man Winter can be a ruthless, unforgiving teacher for the wildlife of Minnesota. Indeed, the ability of nature's wild critters to adapt, endure and ultimately survive subzero temperatures, deep snow, high winds and even rain is a fascinating case study in self-preservation that plays out across our state. Think beyond the confines of the recent thaw in some parts. Winter has yet to have the last word.

Migratory birds like ducks and some songbirds flee winter's grip for warmer and food-rich southern climes. Amphibians and mammals hibernate. Raccoons and squirrels take refuge in their dens for days at a time.

Some call it the survival of the fittest. Others call it natural selection, evolution at work.

"Winter in Minnesota can be harsh. Some species die. But, in general, wildlife have developed an amazing ability to adapt to their circumstances," said Steve Merchant, wildlife population and regulations manager with the Minnesota Department of Natural Resources. "This winter has been unusual, to say the least. We started out really warm around the deer-hunting season, then it got cold and snowy in some areas, and it rained like crazy on Christmas."

Historically, Merchant said, this winter hasn't been "real severe."

"As we've learned, however, winter can last throughout March and even into April," he said. "We're not out of the woods yet."

Here's a look at how several wildlife species get through the winter.

Ruffed grouse

A native forest species, ruffed grouse rely on deep, powdery snow in which to roost and evade predators. "The snow acts like insulation and creates an area that covers them," said Charlotte Roy, DNR grouse research scientist, adding it's considerably warmer inside snow roosts compared to the ambient temperature. "Grouse will literally dive into the snow from trees." Ruffed grouse also grow comb-like membranes on their feet that allow them to travel over deep snow more efficiently. "They provide greater surface area and act like snowshoes," she said.

Currently, snow conditions are poor for ruffed grouse. Freezing rain and snow melt have created crusted snow, which in turn makes it harder for grouse to escape and evade predators such as raptors.

Pheasants

A nonnative game species, pheasants rely on thermal cover (cattail sloughs and shelterbelts) to survive winter. During harsh winters with deep snow and cold, pheasants have to abandon winter cover to search for food. In doing so, they deplete their fat and muscle reserves and expose themselves to predators.

"It's calories in and calories out," said Nicole Davros, DNR upland game project leader. "Pheasants can go up to two weeks without eating, but they can also lose 50 to 60 percent of their body weight."

Pheasants rarely starve to death during severe winters.

"Pheasants aren't like native bird species that have adapted to winter," Davros said. "Pheasants can die of hypothermia when they're exposed to a significant weather event, oftentimes while they're searching for food. Ice will build up under their feathers and they'll die. Starvation is rarely the cause."

Pheasant morality can reach 75 percent during a severe winter. "The good news is that is hasn't been a bad winter for pheasants so far," she said.

Black-capped chickadees

Often found at winter bird feeders, the popular, tiny bird has an uncanny capacity to survive harsh winters, said Katie Burns, outreach and education coordinator with Audubon Minnesota.

"Some people think they're suburban wimps, but they're not," said Burns.

To conserve energy and to ultimately survive in frigid temperatures, Burns said chickadees go into regulated hypothermia to lower their body temperature in a controlled manner. That regulated state, she said, is about 12 to 15 degrees lower than their normal daytime temperature of 108 degrees. "It's a unique adaptation," she said, "and it allows chickadees to conserve close to 25 percent of their hourly metabolic expenditure when it's at or near freezing outside."

Whitetailed deer

Whitetailed deer survive winter by living off their fat reserves, which are bolstered in summer and fall. Deer stay warm with a layer of fuzzy underfur that acts like insulation and helps trap body heat, said Glenn DelGiudice, a state moose and deer project leader.

Quality food becomes scarce in November and early December, and DelGiudice said deer undergo a physiological adaptation that slows their metabolism to conserve energy. He called the experience a "hormonal chain reaction" triggered in deer that shifts them into conservation mode. "Northern deer are all about energy conservation in winter."

While farmland deer have access to more high-calorie food sources such as corn, forest deer must survive on a less-nutritious, woody browse for nourishment. During historically severe winters, mortality can reach 30 to 40 percent. "That's rare, but it happens," said DelGiudice. "It's typically between 5 and 12 percent."

During severe winters with prolonged deep snow, forest deer can succumb to predation. "Wolf predation is the primary proximate cause of death for forest deer, but under-nutrition is a primary contributing factor," said DelGiudice, who added that "a good winter for deer is a harder winter for wolves."

With less snow, deer have a better chance to escape wolves. "Seven inches of snow is like walking on bare ground for deer," he said.

This year's relatively mild winter has both farmland and forest deer in good shape. "We've had a fairly mild winter to date, so most deer should be in good body condition."

Black bears

Bears hibernate in a variety of dens, living off their stored body fat (they can lose up to 30 percent of it during hibernation) for up to six or seven months. During this period, bears don't eat, drink, urinate or defecate, but recycle their bodily wastes and wake usually with little muscle loss sometime in April.

"If we didn't move for six months, our muscles would atrophy and we couldn't get up," said Dave Garshelis, a state bear project leader. "But bears are able to take right off and move quickly."

Hibernating bears cut their metabolic rate in half and hold their internal body temperature at about 91 degrees, roughly 10 degrees colder than their normal summer temperature. Their heartbeats per minute decrease too, averaging about 20 and as few as eight. Very few bears are lost to starvation or wolf predation in winter, as some believe. "It's very, very rare," Garshelis said.

When bears rise in April, their metabolism quickly cranks up. They need and want to eat. If they're in poor body condition, they could starve.

"Minnesota is stingy with food in early spring," he said. "That's when they're more likely to starve."

Tori J. McCormick is a freelance writer from Prior Lake. Reach him at torimccormick33@gmail.com.