Wintertime Porcupine

It was an early morning at the Cable Natural History Museum as I loaded up the van with our MuseumMobile totes, gearing up for a full day teaching about animal adaptations in the schools. Every Being has a fascinating set of adaptations that help them to survive in their habitat, and it is one of my favorite topics to teach about.

Heading north on Highway 63, the beautiful scenery never fails to keep me entertained as I drive through the picturesque nature of the Northwoods. While my thoughts wandered, a large dark spot high in a distant tree caught my eye. At first, I thought it might be a squirrel drey–a large nest of twigs and leaves built high in a tree. But as I got closer, I realized that it was a porcupine! Once my excitement calmed down, curiosity began to take its place. I began to wonder why exactly this porcupine was high up in the tree on this late fall morning. The answer may lie within the feeding strategies of the North American porcupine.

Once the vegetation has begun to go dormant for the fall and winter, porcupines change how they forage for food. They shift from their spring and summer strategy of feeding on ground vegetation and leaves to heavily relying on trees and shrubs in the fall/winter, often spending large amounts of time in a single tree. They target the cambium and phloem layers, the living, growing area between the bark and the water-carrying sapwood, responsible for transporting sugars. This transition from a wide variety of foods available in the summer to nibbling trees in the winter is a drastic drop in nutritionally valuable food for porcupines.

A porcupine high up in an Aspen tree. Photo by Emily Stone. 

Porcupines, like many animals, eat a large amount of food in the summer to put on weight for the coming winter. On average, porcupines will begin winter with around 50% body fat–similar to a polar bear or seal. However, porcupines have thrown the typical winter survival strategies to the wind. They don’t hibernate to avoid poor food availability, spend time in burrows to conserve heat and energy, or cache food to not spend energy foraging. Instead, they hang out in treetops, exposed to the elements, as they spend energy feeding on food with the nutritional content of cardboard. But recent studies show they still manage to only lose an average of 35% body fat over the winter! This lack of fat loss shows they have adapted to survive on a poor diet in harsh winter conditions. But how?

Studies show that a porcupine's metabolic rate slows in the winter, lowering their energy intake requirements. These low energy requirements, partnered with a high tolerance for dietary imbalances, moving very little while foraging, and their large fat stores at the beginning of winter allows them to mitigate body mass loss and survive winter.

The porcupine's impressive adaptations don’t stop there. Once more nutritionally valuable food is available, they are able to immediately put those nutrients to work and gain weight back. This is not a typical ability of many herbivores. Even when good food becomes available, other herbivore species are unable to quickly change how their bodies are being regulated and processing food, making them incapable of properly using those nutrients, and unable to gain weight immediately. Once again, the porcupine is proving to be an extremely adaptable species.

One of the best known adaptations of porcupines are their quills. These walking pincushions sport roughly 30,000 quills–specialized, hollow hairs that cover the porcupine's body. Quills are a porcupine's main defense against predators, and are a particularly mean one. As if getting stabbed by pointed quills isn’t enough, each quill is equipped with microscopic, downward pointing barbs. Once embedded into flesh, the barbs catch on tissue like many tiny fishhooks, making removal viciously painful and dangerous if the quill breaks off inside the tissue. But the brutality of a porcupine's quills doesn’t end there. Those tiny barbs hook farther into flesh the more the victim moves, and body heat makes them expand–making them even more painful and difficult to remove the longer they are embedded.

Close up with a porcupine. Check out those quills! Photo by Emily Stone. 

Between their unusual adaptations to survive winter, and their intricately hazardous quills, porcupines are a natural wonder. I could be entertained for days by the complex adaptations they have developed to survive in their habitat. Much to my surprise, while driving back along Highway 63 after teaching all day, the porcupine I saw earlier that morning was still there. No doubt they were putting those winter adaptations to use as they foraged for twigs and bark high in the tree.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Winter Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

The Subnivean Zone Returns

Lake Superior was astonishingly calm as we walked out to a rocky point in the last rays of the setting Sun. With no wind and temperatures well above normal for late November, my fiancé and I only needed light sweaters and jackets to stay warm. It was a truly lovely day to be outside.

Lake Superior on a calm November, day. Photo by Emily Stone.

Lake Superior on a calm November, day. Photo by Emily Stone.

“Grandfather Alden would have called this a ‘weather breeder,’” I told Kevin. He didn’t read The Boxcar Children books by Gertrude Chandler Warner, but they were a staple of my childhood. In this early reader series, four brave siblings solve quaint mysteries with the help of their wise grandpa. In Snowbound Mystery they spend a glorious, bluebird day hiking around a mountain cabin before a blizzard socks them in. Their Grandfather called the bluebird day a “weather breeder.”

On The Weather Channel’s website, I found this explanation to confirm Grandfather Alden’s usage: “According to a late 19th century definition, a weather breeder is a beautiful day of ‘unusual fineness’… However, such a day is usually followed by bad weather.” A 1996 article about weather adages in The New York Times explains that the only science behind that saying is the law of averages. Good weather doesn’t cause bad weather, but since the weather is always changing, your good weather will soon turn to bad. Checking my weather app, I was thrilled to see the amount of snow in the forecast going up yet again. This day was certainly the calm before the storm!

Cold rain splattered my windshield the next day as I headed back to the shores of a smaller lake in Northern Wisconsin. Before cozying up indoors, I wrapped my digital thermometer in plastic wrap and tucked it under the bright green frond of an evergreen wood fern in the yard. This has become an annual ritual. On the weather station screen indoors, I could see that the newly placed sensor matched the air temperature in the mid-30s.

Can you see the white corner of the temperature sensor hidden under the fern?
Photo by Emily Stone.

Overnight, the wind howled and rain turned to snow.

As winter’s first snowflakes drifted through the dark, some landed on top of dead plants, fallen leaves, twigs, and other detritus of the forest floor. In many places, snow never fully reached the ground. That was surely true for the protected hideaway of my thermometer. By dawn, it was buried under six inches and counting.

Despite falling temperatures, the relative warmth of the cold rain and the residual heat of summer were still radiating from the soil. At sunrise, when I checked the weather station, the air temp had dropped to 24 degrees Fahrenheit, but the sensor cozied up to the earth under a fresh blanket of snow read 33 degrees. After two winters of thin snow, the Subnivean Zone has returned!

All winter long I will monitor the air temperature and the temperature of a thermometer I recently buried in the Subnivean Zone under the snow. In it’s first day of existence this winter, the Subnivean Zone did not drop below 33 degrees! Photo by Emily Stone.

In this magical space, with a blanket of snow to trap the earth’s warmth and provide a solid break against the windchill, temperatures hover around freezing even as the world above drops below zero. Deeper snow provides even more insulation, and all manner of Beings—from mice to martens, bacteria, fungi, spiders, hibernating insects, frozen wood frogs, and more—rely on the moderated microclimate.

In 2022-23—the winter of record-breaking snow—deep drifts accumulated on still-thawed ground, and the temperature in my front yard’s subnivium didn’t drop below 32 degrees for the entire season. The last two winters haven’t been so lucky. With thin, icy snowpacks, plant roots and mosses felt the sting of dry, bitter cold, ruffed grouse couldn’t dive into a snow cave to spend the night, and small mammals had to face the choice of staying safe and warm in a burrow, or risking being eaten or dangerously chilled while they foraged for food. Wood frogs in the leaf litter suffered without snow to buffer them from energetically costly freeze-thaw cycles.

Happily, at least for this week, those Beings are safe from the challenges of a snowless winter. Those Beings include me. Cold weather without groomed ski trails makes me sad. This week, my social media feed is full of good news about trails opening.

A weather breeder might be a day of “unusual fineness”, but I personally wouldn’t call what came after it “bad weather.” For many Northwoods Beings (the ones who don’t have to drive on bad roads or clear downed trees) snow and The Subnivean Zone are truly something to be thankful for!

Fluffy snow is a wonderful insulator to help retain warmth from the earth. Fluffy snow is also great for skiing up a gravel road! Photo by Emily Stone.

Emily’s brand-new third book, Natural Connections3: A Web Endlessly Woven, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

https://www.cablemuseum.org/books/ 

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Winter Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.