Winter Survival Strategies for a Grouse, a Weasel and a Flea

We take a look at two animals and an insect for clues to how life in the wild makes it through a long, cold winter in Northern Michigan. Hibernation? Forgettaboudit.

Surviving  the bitter cold of Michigan winters requires pluck, resistance—and strategy, strategy, strategy. Whether it’s plummeting into snowbanks, hiding animal carcasses in hollow logs, or snacking on fungal spores at the snow’s surface, these three creatures manage to whoop it up in winter—probably in your own backyard.

Of all the resident animals suited to survive the long, unforgiving winters in the North, we humans are the most pathetically ill-equipped. Never mind our cocksure sallying forth into the wilderness, our extreme sports. Here’s a reality check: sans all our Northface outerwear, we die after a mere 15 minutes of exposure at -40˚F, a temperature easily reached with a wind chill factor. But out the back door and just beyond the woodpile exist strange and marvelous animals whose very familiarity hides their superb ways of coping, even thriving  in the cold and snow. If we step outside to the snowdrift, perhaps we can spy on some of winter’s chosen creatures. And hairless one—don’t forget your mittens.

In the often birdless silence of winter, you may be surprised to see that the scrappy ruffed grouse is out, around, and living it up. They’re at their most relaxed and active when the snow falls, taking advantage of a landscape offering fewer predators and less competition for food. Their adaptation begins with a change in diet and boost in metabolism (a winter bonus point, considering most animals’ metabolisms drop  20–80 percent). They prefer to gorge on aspen flowers, but can shift gears if necessary. “They’re opportunistic, tough little birds,” says biologist and grouse expert Rick Baetsen. “If there’s something else there to feed on, they’ll eat it.” Buds, shoots, berries, you name it. Grouse have to stoke that inner furnace—to stay active in 20˚F, they eat 20 percent of their body weight each day, the human equivalent of starting off your day with eight boxes of cereal and ending it with 20 pounds of lasagna.

But what’s horsepower without traction? You need special gear to get around in ice and snow, and the ruffed grouse grow their own. In the fall, they develop little studs on their feet called pectin. These horny growths act like snow tires, helping the birds navigate the icy crust that forms on the snow and branches. With all this exposure, a bird needs to watch heat loss. To this end, the grouse’s legs are feathered, helping to keep heat from dissipating. These ersatz leg warmers are aided by a bird trick called rete mirabilis, or countercurrent circulation, in their feet and legs. This means the arterial blood is on the inside of the leg where it will lose less heat, and the cooler venus blood is on the outside, so feet and legs can drop in temperature without compromising the overall body temperature as much.

But the pièce de résistance? Grouse keep warm with a curious bedtime ritual: they fly straight up into the air, scope out an open space full of drifts and free of obstacles, and dive bomb into the snow. “It’s called snow roosting,” explains Baetsen. From their initial landing, they’ll wriggle another 10 to 20 feet in order to get safely away from the telltale entry point. “It’s a very effective strategy,” he adds. “This way, they don’t leave tracks for predators to follow.” There, they find haven beneath the snow, where air pockets hold warmth from the earth,  maintaining a constant temperature that can be up to 70 degrees warmer than the air above. It’s not a strategy without hazards. Years where snowfall is scant find grouse plopping themselves into shallow drifts like ostriches with their heads in the sand. Layers of ice or hidden objects beneath the snow can result in broken necks or (gulp) impalement. And collapsed burrows in shallow drifts are a beacon to predators, a broad hint that the something below is cluelessly enjoying a long winter’s nap.

Somewhere beneath that same snowdrift, tunneling to the left of our roosting grouse friend, lurks one of the most well-adapted predators winter has to offer: the short-tailed weasel.

You may know them by their other name—ermine, as in the cape-trimming fur of choice among royalty. Much of the year, northern weasels are clothed in plain brown fur, but in winter their coats turn brilliant white, with only the black tip of their tail to give them away.

Blending in is a good strategic bet, helping animals to hide and hunt more effectively. But how does a weasel “know” how or when to shed drab brown for dazzling white? Glenn Dudderar, associate professor of Fisheries and Wildlife Biology at Michigan State University,  explains that the change in coloration is regulated by daylight, not temperature. When short days follow long days, the pituitary gland gets signals from the eye. The gland then secretes hormones that cause a chain reaction until the appropriate chemical cocktail has been mixed. The summer hair gradually sheds, and the new hair that grows is a stylish winter camo.

Although it’s very effective, seasonal camouflage is also risky. What happens in milder years like 1997, when you have spotty snowfall or none at all? “Disaster,” Dudderar warns. “You see an animal that adapts like this and think, ‘isn’t nature wonderful?’ That’s a lot of crap. Nature is fickle. In a winter with little snow, animals with adaptive coloration get clobbered.” A white weasel in brown woods is a conspicuous predator, not to mention an easy target itself for owls and goshawks.

Fortunately, the weasel is no one-trick pony. Beneath that camouflage, their narrow, flexible bodies are efficient and well-designed machines, suited for following prey into their tiny dens and tunnels beneath the snow. Such a predator needs to keep fueled, so as winter approaches weasels whip into hyperdrive and eat like crazy. The excess food becomes brown fat, a special type that produces more energy than regular fat when metabolized.

These animals don’t count on stored fat or winter hunting to carry them through a long winter, though. Enter Plan C: When things are flush, weasels hide their prey carcasses  for future consumption in hollow trees, logs, even the victim’s own den. Den robbing is another useful trick. “Not only do you get a nice burrow, you get to eat the occupant!” Dudderar says, clearly impressed by the weasel’s weaselness. But sometimes winter is too harsh and unforgiving. During lean spells, even the voracious weasel knows to lay low and save energy. Females delay implantation of their embryos, which hover in a kind of stasis until spring, when the mother will have more energy to nurture growing babies. And when it comes time to choose between heading off into the snow to hunt or conserving energy, the weasel and most other animals will choose to conserve, curl up, and wait it out. “Animals are wiser than human beings,” says Dudderar. “In bad weather, they know when to hunker down. Humans don’t. That’s why they end up on ‘Rescue 911.’ ”

Now look down, there, in that sunny spot on the snowbank. See that ashy shadow? Wait, is it moving? What are those thousands of bouncing specks!?! Ah yes, someone forgot to tell you it’s snow flea season.

Before you give an involuntary shudder, let’s clarify. “Snow fleas”(hypogastrura nivicola) are not fleas at all, but are commonly called springtails, so named because of a spring-loaded apparatus at the end of their body that makes them “hop.” They’re incredibly common, part of a primitive, wingless class of insect-like creatures called collembola. Springtails are active year-round, but in winter they party in huge hoards on the snow’s surface.

When winter loosens its grip a little, a spot of sunlit snow lures the springtail out from its lair in the leaf litter at the base of trees. There, on the snow’s surface, the tiny 2 mm-long animals feed on a veritable buffet of algae, fungal spores, and bacteria.

Most insects migrate or hide out in winter, when it’s too cold for their bodies to really  function. But snow fleas have a few tricks to keep a spring in their step. For one, they are darker than related species, an adaptation that helps them absorb solar radiation. Another perk is the make-up of their blood chemistry. Because they lack the kind of internal furnace that other animals have, a typical insect’s blood would begin to form ice crystals as the temperature dropped— “and then you’ve got a dead duck on your hands,” explains Dr. Richard Snider, entomologist and professor of zoology at M.S.U. Ever freeze lettuce or spinach?

When it thaws, it’s hopelessly limp. That’s because the water crystal formations have punctured and destroyed the cellular structure of the tissue. Snider reveals the springtails’ secret: Their blood contains glycerol, which prevents crystal formation by acting like antifreeze. “That’s why their species name is nivicola, which means ‘snow lover,’ ” he adds. Try that one out on your friends.

All in all, it’s a good life. Food is plentiful, and the usual predators like spiders, mites and crickets are snoozing through the season. The springtail takes this relatively safe and bountiful time of year to gather in huge masses and take care of business that would be risky with predators around:  “They congregate to mate,” says Howard Russell, entomologist at the Center for Integrated Plant Sciences at M.S.U. “In a sense, it’s a big orgy.”

These enormous gatherings are easy enough for the amateur naturalist to spot—just look for a sunny area near the base of a tree, and you may see quite the swarm. Sometimes they cover entire acres. “I get calls throughout the winter,” Russell says. “I think any time people see thousands of ‘fleas’ it unnerves them. They won’t let their cat out, they won’t let their kids play in the yard.”

So we’ll call them springtails and we’ll step lightly in the sunny spots, because you never know what’s afoot—or underfoot—in the snowy corners of the winter landscape.T

Cara McDonald is a former assistant editor of TRAVERSE. She now lives and writes in Colorado. This story first ran in Traverse, Northern Michigan’s Magazine in February 1999.

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