Weighing in at up to 40 pounds (though usually 8-15 lbs), the porcupine is one of the largest North American rodents, second only to the beaver. Erethizon dorsatum is perhaps best know for its quills which cover much of its body. This prickly protection usually keeps it safe from all but the automobile, for which quills are useless. In fact, about half of all porcupines I’ve seen were road kill. In the spring they crave salt, and sometimes make the unfortunate choice to visit the highway to get it.

The rest of the porcupines I’ve seen were in a den, on a tree, or casually strolling the forest floor. They’re not usually in a hurry, because they don’t need to be. Most attackers get a face full of quills. Its slow moving nature, arboreal tendencies, and general appearance are somewhat reminiscent of the totally unrelated sloth, though porcupines are not so slow as to harbor moss.

Porcupines usually inhabit forested areas over most of Canada and the western, mid-western, and northeastern United States, as you can see in its range map here. Here in Massachusetts, they seem particularly common the Quabbin Reservoir region. Check out our Wildlife Tracking Programs if you’d like to come learn with us!

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Porcupine Tracks and Sign

Porcupine tracks and sign are most easily observed in winter. These animals remain active all winter, and their runs, feeding sign, and scats are easy to see on snow.

Feeding sign

Nipped twigs

As an herbivore, the porcupine’s diet varies by season, according to the availability of plant foods. In summer, they may eat herbaceous plants in fields, but throughout the rest of the year, they feed on woody plants. They consume bark, twigs, leaves, buds, and mast (fruits, berries, and nuts) of trees and shrubs.

The porcupine is an excellent climber, but too heavy to venture out to the distal twigs. To reach coveted delicacies, it uses its sharp incisors to cut a length of twig. After feeding on the buds, young leaves, or mast, the animal drops the nipped twig to the ground. So, under favorite feeding trees, you can find these nipped twigs. Look carefully at the cut end of the twig nipped by a porcupine, and you will notice an angled cut, typical of twigs cut by rodents.

In fall, when porcupines eat a lot of acorns and beechnuts, look for nipped twigs under oak and beech trees. In winter, when they eat the foliage of hemlock and spruce, look for nipped twigs under these trees. In spring, you might find nip twigs under sugar maple, white ash, and aspen, from which they eat the buds and young leaves.

Porcupines are creatures of habit, often returning to feed on the same tree, night after night. These favored trees become so heavily pruned, that they develop a stout and stunted bonsai-like structure.

Bark

Like many other herbivores of the temperate forest, porcupines feed on the bark  of woody plants in winter. In fact, they have gained notoriety among foresters for damaging trees in this way. You can’t miss the gleaming yellow, debarked patches on hemlocks and oaks in the stark winter landscape. They may feed on bark anywhere on the tree, and may (rarely) debark an entire tree.

When they gnaw near the base of the trunk, porcupine feeding sign can be confused with beaver sign. But porcupines gnaw only deep enough to feed on the nutritious cambium. The have no reason to gnaw into the wood. As excellent climbers, porcupines can access branches and twigs without taking the tree down. Beavers on the other hand, cannot climb, and must bring the tree to the ground to access twigs and branches for both food and building material.

Scat

Porcupine scat is produced in discrete pellets, especially in winter when they are feeding on the dry material of woody plants. The pellets are about an inch long. Some of them look like deer pellets, but many are curved and resemble a cashew nut in size and shape.

Tracks and trails

Porcupines tend to use the same feeding trees repeatedly, which makes their presence quite obvious.  Where porcupines are present it’s easy to find these runs in snow. But because they travel over the same trails repeatedly, finding a perfect, un-trampled track is a rare event. I still kick myself over the lost opportunity for a photo of a perfect porcupine track in a dusting of snow. The tracks were so clear, you could see the pebbling on the bottom of the foot. But that was many years ago. I was a beginner, and did not appreciate the rarity of that finding.

Dens

Porcupines like to den close to a good food source, but other than that, they’re flexible in their choice of den site. In spring, a mother might leave her baby in the shelter of a fallen log, while she sleeps alone in a tree. In winter, porcupines seek shelter in ledge, between boulders, in cavities at the base of trees, under the roots of upturned trees, in outbuildings, and even in abandoned beaver lodges. In winter, they don’t seem to mind dens with wet floors, as long as the water is frozen.

Winter dens are used repeatedly, and porcupines make no effort to keep them clean. Scat will be evident on the floor, and sometimes it’s spilling out of the den in great quantity.

The scat accumulation in winter dens is an interesting issue. Some suggest that it’s of insulating value to the occupant, but it may be of no advantage at all. Perhaps there is simply no disadvantage to scat accumulation. It does make the den obvious to predators, but a porcupine in a den does not need to worry about predators. It turns its face to wall and displays its tail, and anyone who doesn’t want a face full of quills will not attack.

Quills

Porcupines molt their fur every spring, but drop quills here and there. You might notice a few among the scats of a well used den, and occasionally find one along a well worn run. Quills are stiff, lightweight, modified guard hairs, but they are not hollow, contrary to popular belief. They are actually filled with a spongy matrix of tissue.

Another popular misconception is that porcupines shoot their quills at predators. They do not. However, the quills do detach easily when touched, and microscopic barbs make removal difficult, once embedded in flesh.

Sources:

1. Elbroch, Mark. 2003. Mammal Tracks and Sign: A Guide to North American Species. Stackpole Books. Mechanicsburg, PA.
2. Reid, Fiona A. 2006. Mammals of North America. Houghton Mifflin Company. New York, NY.
3. Roze, Uldis. 1989. The North American Porcupine. Smithsonian Institution Press, Washington, D.C.