“Thorny Pigs” Feasting on Pine Bark

by Kevin Strauss

During a walk through the woods, you might see what looks like beaver chews on a pine or aspen tree. But unlike a beaver chewing, which involves cutting down a tree, these chews seem only geared toward devouring the inner bark of the tree itself. The chew could be at the base of a tree, at high in the branches.

This animal sign is evidence of a large rodent that few people ever get a chance to see: the porcupine (Erethizon dorsatum, literally “thorny pig”). This chubby, slow-moving, long-haired creature spends much of its time feeding or resting up to sixty feet up a tree.

This time of year, these solitary creatures are reduced to feeding on the nutrition-poor inner bark of red or white pine and aspen trees. Even with this food, porcupines loose weight through out the winter. Porcupines who hadn’t fattened themselves up on acorns, leaves or pond lilies last fall, might even starve to death before the green plants emerge again in the spring.

Porcupines range from 2-3 feet in length, including an eight-inch muscular tail. They weight between 15-18 pounds and at birth, the single “porcupette” is larger than a newborn bear. They have excellent senses of hearing, smell, and taste, but are quite nearsighted.

In some ways, the porcupine is our own version of Australia’s koala bear. Both porcupines and koala bears (who aren’t actually bears) spend much of their feeding in the trees and using them as a safe place to avoid predators. But unlike the koala bear, porcupines have an additional defense to protect them from their enemies: 30,000 barbed quills.

These 1-3 inch porcupine quills are actually modified hairs, hidden among the long, dark guard hairs on its back and tail. When the porcupine is relaxed, the quills lie flat against the skin. But when they feel threatened, their muscles tense and the quills stick up, ready to defend the porcupine from dogs, wolves, coyotes and their most fearsome enemy, the (large weasel-like) fisher.

When threatened, a porcupine tucks its head, turns its rear end to the enemy and thrashes with its quill-laden tail. With as many as 100 quills per square inch on a porcupine’s tail, any predator that is new to porcupines will probably end up with several quills embedded in its face and mouth. What’s more, the barbs on a porcupine quill will work their way deeper and deeper into the animal’s skin. A predator might starve if it can’t remove the quills piercing its mouth. At the very lest, the creature will receive a painful series of quill wounds. Porcupines can’t “shoot” its quills, but the quills are so loosely attached to its skin, that the lightest touch from will leave them embedded in a person’s hand or a wolf’s muzzle.

When they aren’t feeding on tree bark these days, porcupines retire to dens in hollow logs, rock caves or the thick vegetation of evergreen trees. Unlike some other northwoods mammals, porcupines are active throughout the winter, but since they are usually only active at night, we don’t often see them moving. So the next time you are walking in the woods, look up into the trees, you might just get a look at a napping thorny pig, 60-feet up in a tree.

The Ely Timberjay