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.