Wednesday, February 22, 2012

Mouse Snacks

The light dusting of snow we received the other night was the perfect substrate for mouse tracks.  The morning light revealed a mouse freeway leading from the stack of flower pots to the mess of seed under the bird feeder. Their tiny tracks look like a smaller version of red squirrel tracks.  Mice and squirrels both hop by placing their smaller font feet down first, then bringing their larger hind feet around the sides.  As the hind feet hit the ground in front of the front feet, they give a mighty push for the next hop.  Rabbits also move in a similar way. 

You can decipher an interesting bit about the ecology of a hopping track-maker by the placement of their front feet. Arboreal animals, those who spend a lot of time in trees, will place their front feet right next to each other, perpendicular to their line of travel.  Squirrels do this, and a little surprisingly, deer mice are excellent tree climbers and therefore are sometimes paired-front-foot hoppers. Rabbits and hares, who are not often observed in trees, place their front feet with one ahead of the other, at an angle to the direction of travel.  Can you decipher all the tracks in your yard?

The appearance of deer mice – light brown back, white belly, and big ears – is reminiscent of a white-tailed deer.  Mice have much longer tails, though, which aids in their tree climbing.  Deer mice have a closely-related and almost indistinguishable cousin, the white-footed mouse.  To tell them apart, experts look at a difference in the amylase molecules of their saliva.  You might remember amylase from biology class when you chewed on crackers until they tasted sweet.  Amylase is an enzyme that breaks carbohydrates into simple sugars.

Food is especially important during the winter for these tiny active critters.  Mice will cache food (including weed seeds, birdseed, berries, and my cookie crumbs) in the fall, and throughout the winter.  Several times I have curiously brushed the snow off of an abandoned bird nest and discovered a tidy little mouse pantry.  Earlier this winter I accidentally left a Mason jar with birdseed in it on the patio.  I found it a few days later, with the contents spilled onto the snowy path.  Squirrel tracks, mouse tracks and tunnels surround the windfall as they busily hoarded the treat.

Eating plenty allows the mice to run their metabolism on full speed to keep warm.  In the winter they add new red blood cells with more hemoglobin to fuel their roaring metabolism. After creating all that heat, mice do their best to conserve it through the day when they are not active.  Body temperatures may be allowed to drop as they snuggle in next to other mice in a cozy woodpecker hole, thatched-grass nest, bluebird box, or the warm micro-climates of our homes.

Peering out of my home early one morning, I witnessed a bit of natural drama.  My local gray fox stood on the path by the corner, in person, not just in tracks! He was just ten feet away, standing over the remnants of spilled birdseed.  In the shadowy pre-dawn, I watched as he nuzzled the snow and came up with a limp mouse hanging from his jaws.  With a flick of his head, the mouse disappeared in one gulp. The fox trotted nonchalantly down the path leaving delicate tracks in the fresh dusting of snow.

In December, the fox tracks whispered “Listen…it is music to run over the hills” Now he adds: “Death itself is a music…It is flesh and bones changing shape and with good cause. Mercy is a little child beside such an invention.” (Straight Talk from Fox in Red Bird by Mary Oliver). 

For over 44 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M. The new exhibit, The Joy of Birds: Feathers in Focus opened in May, 2011. Find us on the web at to learn more about our exhibits and programs. Also discover us on Facebook, or at our blogspot,

Love is in the Air

It's mid-February, near Valentine's Day, and love is in the air. Literally. Many animals are anticipating or are in the midst of their breeding seasons right now, and they are advertising it through air with sound and scent. You've probably heard a few eager chickadees singing their "hey sweetie" love songs despite below-zero temps. They won't breed until April, but it doesn't hurt to get a head start impressing the ladies, right?

If you have owls near your home you may be hearing their eerie calls more often. Great horned owls and barred owls both mate this time of year, and are calling back and forth to communicate both with potential mates and potential competitors. One of the great horned owls' prey species, the wild turkey, has also been noticed strutting to impress the ladies recently.

Wolves have already been thinking amorous thoughts for a month or so. You may have heard them howling along with the owls. Within a pack, typically only the top male and the top female (the alpha pair) mate. They will announce their intentions with a "paired RLU." This is where the male initiates raised leg urination (RLU) to leave a scent mark, and the female then urinates next to his. If the female is in estrus, you may see a few drops of blood on the snow.

Bobcats are typically a solitary species, but this time of year the males and females will strike a tentative truce for mating season. Males and females will increase their scent marking behavior, which may help them learn about potential mates, and find each other when the time is right.

Two of the bobcats' favorite prey species, gray squirrels and red squirrels, are also starting to feel amorous. You may have noticed that the squirrels have been extremely active recently. Their mating rituals begin with a chase, as up to ten males compete for one female. Their arboreal acrobatics can be quite entertaining. Male squirrels can smell when a female is in estrus and ready to mate. This is a useful skill, since she is only fertile for one day.

Often in mid-winter I will notice little splotches of red in the squirrel tracks around my bird feeder. I haven't been able to find any information relating directly to this, but my guess is that it's a sign that a female is in proestrus, and, just like the wolf, is leaking a little blood. As spring keeps peeking at us from around the corner, we will continue to see even more amorous behavior in the woods.

What are your plans for Valentine's Day? Perhaps you will consider wooing your date with a sweet song or a designer perfume!

For over 44 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M. The new exhibit, The Joy of Birds: Feathers in Focus opened in May, 2011. Find us on the web at to learn more about our exhibits and programs. Also discover us on Facebook, or at our blogspot,

Ode to the Glaciers

What do you love most about Northern Wisconsin? Rolling hills traversed by some of the best trails in the country, winding back roads, sparkling lakes, and shady green forests are some of my favorite features. Have you ever wondered why all these wonderful things come together in Northern Wisconsin? Maybe you know that this region was shaped by glaciers, but have you ever really sat down and appreciated all that the glaciers did for us?

I love glaciers. I have never seen one in person, and yet they have vastly improved my quality of life. Whether you realize it or not, you also know the joys of glaciers whenever you whiz down a rolling ski trail, hike merrily up and down hills, enjoy the stomach-dropping exhilaration of catching air on your snowmobile, or boat and fish on one of Wisconsin’s more than 10,000 lakes.

The landscape around Cable and Hayward was shaped during the Wisconsin Glaciation (named for us!) of the Quaternary Ice Age (which is still going on in Greenland and Antarctica). It began about 100,000 years ago, hit its maximum extent about 21,000 years ago, and the last glacier had retreated out of Wisconsin into Canada by 10,000 years ago.

The very recent (geologically speaking) visit of a glacier here has had a profound impact on what the landscape looks like. As glaciers advanced across the land they scraped and carved and plucked up rocks from their path, and carried them along within the ice mass. Like a conveyor belt, they brought tons (literally) of sediment south with them. Two lobes of ice flowed into our area, and their lateral margins met somewhere near Cable.

Where we really start to get interested is when the climate warmed and the ice began to melt faster here at its toe than new snow from Canada could replenish it.  Huge chunks of ice were left behind from the melting edges of the glacier, and then glacial outwash rivers carrying meltwater and debris off the glacier buried those ice cubes.  Well-insulated, the ice lay hidden under a flat surface of sand, gravel and cobbles for many years.

As the ice melted, basins of all shapes and sizes were left behind where the ice had been. Sometimes these basins, called kettles, filled with water and became lakes, others are perched far above the water table and stay bone-dry. The landscape of sandy, rocky soil pockmarked by kettles is called a “pitted outwash plain.” The Rock Lake ski and mountain bike trails east of Cable are a prime example of this topography, and in my opinion, a prime place for recreation because of it. The Birkie Trail takes advantage of the varied topography so much that its hills are legendary.

In places, the glacial conveyor belt stagnated for a while, leaving a line of jumbled sediment where its margin had been.  This is probably what created the wacky shoreline of Lake Namakagon – with many shallow bays and great fish habitat.

Even the towering spectacle of Mount Telemark owes its existence to the glaciers – rivers flowing on top of the melting ice carried rocks into a large crevasse.  When the glacier melted, a 1,700-foot-tall pile of sand called a “kame” was left behind. It is the tallest kame in Wisconsin.

Not only did the glaciers shape the physical landscape, they, by extension, continue to impact the human uses of it.  Unlike regions to the south and north, we don’t have extensive farming.  Not only are there too many hills, but the soil just keeps growing more rocks. First, water to percolates underneath buried rocks. When it freezes, the ice crystals lift up the bigger rocks and sand falls underneath. Over many freeze-thaw cycles, the rocks come to surface, right in your carrot patch! Happily, many trees grow just fine in this type of soil, so our local crops are forests instead of corn.

The next time you’re out for a spin on a lake, road or trail in Northern Wisconsin, take a moment to appreciate the wonderful legacy of the glaciers.

Friday, February 3, 2012

Subnivean Chronicles

Adventures in the woods lately have revealed fewer species than earlier in the winter. Have you noticed a change? Tracking stories these days are mostly written by little feet, and many of the stories lay hidden below the surface. Now that we actually have a thickness of snow on the ground, a new world develops beneath our feet. This ephemeral habitat is called the Subnivean layer. Since I first learned about this hidden zone as a bright-eyed college freshman, it has taken on a mythical quality in my imagination. Subnivean sounds like it could be a region of Narnia ruled by the White Witch, or perhaps an outpost neighboring Rivendell in Middle-earth.

The Subnivean layer, like so much of life on Earth, owes its existence to the unique chemistry of water. When frozen, water becomes light an airy, a wonderful insulator. Just as down feathers in your jacket trap a layer of air next to your body, retaining the heat you radiate, a six-inch layer of snow traps air that retains heat from the Earth. We don’t have hot-rock geothermal here, no geysers or hot springs. Our ground warmth, used in many local geothermal heating and cooling systems, comes not from radioactive decay in the Earth’s core, but simply from sunlight absorbed into the upper layers of soil and stone.

Because of this insulation and radiating heat, a thin zone opens up under the snow, right at the surface of the ground. As water freezes, it releases a tiny bit of heat, and as it melts, it absorbs a tiny bit of heat. In this way, the temperature in the Subnivean zone is regulated at a pretty stable 32 degrees Fahrenheit. Compared to -20 with a 15mph wind at the surface, that feels pretty balmy!

Many tracks are now being pressed invisibly into the leaf litter that carpets the Subnivean layer. Shrews, voles and mice, small mammals depend on this habitat for food, warmth, and protection from predators. Their presence is betrayed where the tiny jumping tracks of a deer mouse connect small trees with fallen logs. The tunnel of a shrew will suddenly exit the snow at the edge of a ski trail or where snowshoes have packed down a trough. The impossibly small holes can be not much wider than ½ inch. Sometimes shrews and voles will tunnel through the surface of the snow, especially the fluffy stuff, leaving a winding trough that ends in another hole when they again descend into the fabled Subnivean layer.

Although soft and concealing snow may seem like a perfect security blanket, the fat and juicy prey are not safe from their wily and well-adapted predators. Owls can hear mice through the snowpack, triangulate the sound with their asymmetrical ears, and bust through the crust with fisted talons. Foxes and coyotes can also hear and pounce through the crust, thus securing a meal without even seeing it. Our three smallest weasel species – long-tailed, short-tailed and least, are long and skinny with short legs for a reason. They can snake their way through mouse and chipmunk tunnels to catch the critters right in their own dens. Then the weasel will feast and nap at the warm hearth of its meal before going out to eagerly search every tree, log, rock and stump for another tasty treat.

You may also have noticed the prolific squirrel tracks, connecting trees to small holes littered with leaf shards and pine cone scales. Red squirrels will tunnel to find food caches stored last fall, and often put a big hole in the ski track in the process.

Grouse also make use of the warm blanket that snow provides. When the snow is deep enough, they may “roost” by doing a swan dive, leaving no tracks that would lead a predator to their warm bed. In bad weather, a grouse may stay in its burrow for a few days. Back-country skiers and snowshoers tell stories of grouse flushing from these secret burrows just inches in front of their next step.

While many tracking stories are hidden these days, it’s fun to imagine the complex chronicles unfolding in the Subnivean world. What lies beneath the smooth white surface? More than we will ever know.