Last updated: September 10, 2022
Article
Acadia Porcupines
The North American Porcupine (Erethizon dorsatum) is the second largest rodent in Acadia after the beaver. Used in Wabanaki art for generations, the porcupine’s quills have made them a foreboding force to predators and a distinctive sight in Acadia’s woods. Stalky and slow moving, porcupines are ecosystem engineers, shaping plant communities through selective food choices and ground disturbances.
Ashley L. Conti. Friends of Acadia
Habitats
The North American Porcupine is found across most of Canada, Upper Great Lakes region, New England and the Western United States in forests, shrubby deserts and grasslands. In Acadia, the birch and fir forests provide porcupines with many food sources while the rocks and boulders of Acadia’s granite covered mountains are prime real estate for shelter. Porcupines can be found almost anywhere in Acadia in both the deciduous and boreal forests of the Park.
Porcupines are good climbers and can often be found in trees. How much time is spent in trees is highly dependent on food sources and predators. In places where ground cover is scarce, offering little food and shelter, porcupines will spend more time foraging and sheltering amongst the canopies. In Acadia’s forests, though ground cover can be wanting in Acadia’s thin soils, shelter is plenty on the ground with many rocky crevices.
In winter, porcupines in the Park are most likely to be found sheltering among the rocks in dens, possibly with other porcupines huddled up for warmth, but in the tress feeding on bark. In warmer months, you might find the porcupines a bit further up for shelter. Hemlocks are a favorite tree with eastern porcupine for sheltering and eating. Hemlock’s thick foliage offers great sight cover for the porcupine and thermal protection while the sturdy branches make for great perches. Porcupines do not eat the bark of hemlocks as they do in other trees because of the tree’s tannins, but their needles and small branches still offer great nutrition.
Sam Mallon, Friends of Acadia
Size
Porcupines average 18-23 inches long and weigh between 10 to 28 pounds. Porcupines are gender dimorphic with male porcupines growing larger than females. Small in stature, porcupines have short legs and big torsos with a high arching back.
Coloring
Porcupines range from dark brown to black in appearance. Closer examination will show that along their back, porcupines have hairs and quills with bands of yellow. On their lower back and middle of their tail are black lines and the quills there are fringed with white. This black and white coloring stands out at night when porcupines are the most active. Much like with a skunk, this color pattern might be a warning to their mostly color-blind predators (like bobcats or coyotes in Acadia) to stay away or else.
Teeth
Porcupines have 20 teeth: four incisors and 16 molars. The incisors are used for cutting and their molars for grinding down plant material. Like most rodents, a porcupine's front two incisors continue to grow throughout their life allowing for and necessitating extreme use to keep their teeth from overgrowing. Their incisors, like beavers, have a reddish-brown color from iron oxide in the enamel. The iron in their teeth makes them stronger for gnawing on wood.
Feet
Their feet have unique soles that are pebbly textured with fleshy knots and long curved claws. Both help the porcupine to grip trees to climb. Their front paws have four claws and a vestigial thumb, and their back paws have five claws. Porcupine tracks are approximately three inches in length, toe curved in with claw indentations appearing ahead of the pad of the foot.
Porcupines have a distinctive gate, appearing to totter from side to side. Their short legs and chubby bodies keep them low to the ground as they slowly meander.
Quills
Most distinctly a porcupine’s back and tail are covered in quills. A single porcupine has approximately 30,000 of these specialized hairs along their backs and tails. An individual quill is hollow, around three inches long and tipped with microscopic, backwards facing barbs. The barbs help the quill to embed and will also burrow the quill further and further with the muscle movements of the inflicted animal once embedded into the tissue. This further embedment can be fatal.
Porcupines cannot shoot their quills! Instead, these quills are lightly attached to a voluntary muscle that, when stressed, a porcupine will tense to cause the quills to stand at attention. The quills will then easily dislodge from the porcupine and embed into the tissue of their attacker upon contact. The barbs prevent the quill from being removed easily and the tips are easily broken off and remain in the tissue to continue to embed. Porcupines are not immune from being penetrated with their own quills, like when they fall out of trees, but the quills are coated in natural anti-biotics that prevent bacterial growth, likely to protect the porcupine from themselves.
Other Hair
Porcupines do not have quills on their faces, feet or bellies and are instead covered in more traditional and softer fur as well as coarser hairs known as guard hairs. When the porcupine is not tensing their quills, the guard hairs are the more visible covering along their backs. Under their tail, porcupines also have stiff bristles that point backwards. When climbing, these bristles help to prevent slippage.
Will Newton, Friends of Acadia
Eating habits/food sources
Porcupines are strict herbivores. Diet includes woody vegetation, leaves, twigs and green plants. They will forage for food on the ground and up in trees. Porcupines have special adaptations that make them good tree climbers from the bristles on their tails to the pads and claws on their feet. Climbing trees helps to protect porcupines from predators and gives them access to more sources of food. Porcupines take advantage of changing weather with their diet rotating seasonally depending on what food is available.
In the spring, as growth begins on trees, a porcupine might use their tree-climbing ability to nip twigs high up in the branches. While perched on a sturdy limb, a porcupine will use their teeth to nip or cut a smaller twig, pull the branch towards them and munch on the buds sprouting on the ends. During summer months, Porcupines typically forage for food on more solid footing, eating herbaceous greens on the ground like skunk cabbage. Come fall the Porcupines can be found in the trees again, this time nipping twigs to feed on the mast crops such as acorns and beechnuts.
During all seasons, but especially in winter when food is scarce, porcupines will peel away the bark of trees (known as debarking) to eat the softer, nutrient rich cambium layer of the trunk. Many types of trees are found to be appetizing except for those with high tannin levels like hemlocks and red maples. Often you will see evidence of Porcupine debarking higher up on the tree where a porcupine climbed so they may sit and feed relatively safe from predators. Porcupines are also known to dig through the snow to continue feeding on buried plant material—a helpful trait as snow begins to fall in Acadia in November.
Social/ Mating Activities
Primarily nocturnal, porcupines are known to be solitary creatures, but have been observed sharing dens, especially in winter, probably for warmth.
Porcupines mate around October/November. After a seven-month gestation (a long period for a mammal of this size), porcupines will give birth to one (rarely two) young around May/June. Porcupines are born with quills, but they are soft and will harden after a few days.
Porcupettes are fairly mobile at birth and will double their size in the first two weeks. Young will spend 4 to 5 months with mom (a long time for a rodent) while she teaches them about den sites and food before striking out on their own in the fall. Porcupines will not grow to be sexually mature until around the two-year mark. Porcupines often live to be seven or eight in the wild.
Attack and Defense
Quills are the porcupine’s most obvious defense but not always their first choice. Their black and white coloring on their backs and tail are the first warning to potential predators to stay away. If pursued, a porcupine will likely try to retreat, usually up a tree using their climbing skills to evade. They can also release a pungent odor when highly stressed to warn off predators as well.
As slow movers, however, predators certainly have a speed advantage in the retreat strategy. When porcupines begin to feel threatened, they can tense their mussels causing their quills to stand at attention. They will then turn their backs to predators to present their tails which they wave back and forth at the predator's face when attacking. Quills in the face would be painful at best and blinding to fatal at worst for the predator who would most likely retreat upon impact. Because the quills are barbed, they are not easily removed and can continue to embed further into the skin causing bleeding and infection.
While most carnivores in Acadia might enjoy a porcupine, a porcupine's quills are often persuasive enough that predators choose to leave them in peace (or learn a hard lesson when they choose not to). The fisher, the second largest member of the weasel family, might be an exception as the one animal adapted to hunt porcupine.
Unlike taller predators like coyote, fox or bobcat, fishers are the same height as porcupines. This gives them the advantage of face-to-face interaction rather than attacks from above where the Porcupine is nearly entirely covered in quills. A fisher’s greatest advantage is its agility and speed. If a porcupine attempts to flee up a tree, the fisher is agile enough to follow and ultimately chase the porcupine back to the ground. A fisher can use its speed and agility to stay in front of the porcupine (rather than be presented with its tail of quills) and repeatedly attack the porcupine’s face. It is not a quick kill, but it can be worth it for the fisher: a porcupine could sustain them for several days.
Not every hunt is perfect and taking on a porcupine can be risky business, even for a fisher. Unlike other predators, however, while the fisher may end up with embedded quills, the quills appear to be more of a nuisance rather than deadly and the fisher can stave off potential infection.
References
A Fisher's Guide To Preying On Porcupines, Montana Public Radio. https://www.mtpr.org/arts-culture/2019-09-08/a-fishers-guide-to-preying-on-porcupines
Alden, P. (1987) Peterson First Guide to Mammals, Houghton Mifflin Company, New York, NY
Celebrating Hard-Working Animal Moms, US Fish and Wildlife. https://www.doi.gov/blog/celebrating-hard-working-animal-moms#:~:text=While%20porcupines%20are%20normally%20solitary,it%20by%204%2D6%20times.
Elbroch, M. (2003) Mammal Tracks and Signs, Stackpole Books, Mechanicsburg, PA
Erethizon dorsatum North American porcupine, Animal Diversity Web. https://animaldiversity.org/accounts/Erethizon_dorsatum/
Spines and Quills, Animal Diversity Web. https://animaldiversity.org/collections/spinesquills/
What about Porcupines?, Pacific Northwest National Laboratory. https://workbasedlearning.pnnl.gov/pals/resource/cards/porcupines.stm
Whitaker, J.O. Jr (1998) Mammals of the Northeast. World Publications, Tampa, FL