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Porcupines And Their Need For Salt
Over the next several weeks, the buds on hardwood trees and shrubs will open and the forests will again be cloaked in green, providing our many herbivores with a welcome change in their diet. While many plant eaters are able to subsist on woody buds and cellulose laden layers of inner bark throughout winter, leafy matter provides far greater levels of nourishment. The porcupine, a common denizen of the deep Northwood’s forest, is among our region’s first order consumers to ingest greens when they emerge in spring.In winter, the porcupine settles into a routine of eating only the bark and needles of a very few species of trees in the area around its den. The stomach and small intestine of this rodent contain strains of microorganisms that act on this ultra-high fiber material in order to derive the energy needed to remain alive in this climate. Yet the limited amount of nutrients, particularly nitrogen, in such plant tissues makes this type of food less than ideal for maintaining a healthy diet. Despite ingesting large volumes of woody matter each night in winter, the porcupine often loses weight continuously as this bleak season progresses.
Even though this animal has various adaptations to help it conserve the nitrogen that already exists within its system, the porcupine still suffers from a serious lack of the proteins that form the basis of all living tissues. During years when spring comes late, some individuals may eventually die of malnutrition because of their dwindling amounts of nitrogen, even though these gnawing creatures fill their stomach with woody edibles whenever they forage.
The range of the Porcupine in North America
The range of the Porcupine in North America
As buds begin to open in spring, exposing young, tender foliage, the porcupine quickly seeks out these new sources of nourishment. With its exceptionally long and sharp claws adapted for clinging to trees, this chubby, quilled quadruped ascends into the crowns of various hardwoods and ventures out on the limbs in order to access as many emerging leaves as possible.
The abundance of plant proteins in these new leaves helps the porcupine rebuild old, worn-out tissues in its body. It is during this period in spring that the weight of the porcupine finally begins to increase again.
As leaves more fully develop, they begin to form certain chemicals that discourage herbivores from eating them. This is the plant’s means of defense in maintaining its food producing structures. As the initial, light green foliage that characterizes the onset of black fly season transitions into the deeper green of mature leaves, the highly sensitive taste buds of the porcupine direct its intake of foliage to those leaves that contain repulsive agents acceptable to them.
As the porcupine’s diet reverts to leafy matter, certain chemical reactions in its digestive system trigger a depletion of sodium within its body. Other forms of wildlife that have a similar woody diet in winter and switch to leafy matter during the growing season also experience a comparable loss of sodium in their body. For example, both the white-tailed deer and moose increase their intake of salt in summer in order to compensate for the loss of sodium throughout the warmer months of the year. Some people put out a block of salt in order to attract deer or moose in summer, but such an item is also sure to attract the porcupine if one is living in the immediate area. Some objects located along the side of major roadways, where road salt is used in excess throughout winter, may also contain enough salt residue in spring to attract both deer and porcupine. By consuming forms of aquatic vegetation rich in this element, the moose is able to replenish its sodium level without the aid of artificial sources of salt.
Because it is equipped with a sharp gnawing set of teeth, the porcupine is able to chew on any object which contains a small coating of human perspiration. Wooden axe handles and canoe paddles that have been left lying on the ground are both known targets of this rodent. The trace amounts of sodium in the adhesives used in plywood is another sodium source that attracts the porcupine in summer.
The porcupine can inflict occasional damage to various objects around a lean-to, campsite or cabin during the summer because of its craving for salt. People that suffer from high blood pressure should never consider ingesting massive quantities of emerging leaves in spring as a means of lowering their sodium level, as the physiology of the porcupine is quite different from anyone that is not a winter time bark eater.
Top Photo: Porcupine by Mary Harrsch.
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http://northernwoodlands.org/outside_story/article/the-problem-of-porcupines
By ordinary human standards, porcupines have many bad habits. Besides extricating their quills from the noses of pet dogs and livestock, humans must throw out axe handles and leather harnesses chewed beyond use. Porcupines damage, and sometimes kill, trees by gnawing on them; they even gnaw at uninhabited wooden buildings. The human response to porcupines is often an attempt to eradicate them by shooting, trapping, or poisoning.
This wasn’t always so. Among Native Americans in northern New England and elsewhere, the porcupine was prized for its quills, which were dyed and used in decorative work. In winter, especially, porcupines were an important source of meat—honored, along with animals such as deer, for their life-giving qualities. Though porcupines were common in the forests, their numbers were held in check by their main predator, the fisher.
Fisher attacking a Porcupine
Eventually, Native Americans began to hunt fishers for their fur. Then European colonists further depleted fisher populations by trapping them and deforesting the southern part of their range. With a scarcity of natural predators, porcupines have flourished throughout New Hampshire, Vermont, Maine, and eastern Canada.
Fisher attacking a Porcupine
Eventually, Native Americans began to hunt fishers for their fur. Then European colonists further depleted fisher populations by trapping them and deforesting the southern part of their range. With a scarcity of natural predators, porcupines have flourished throughout New Hampshire, Vermont, Maine, and eastern Canada.
Given the porcupine’s unique defense system, it’s easy to see why most predators leave them alone. As naturalist Paul Rezendes notes, the porcupine’s scientific name—Erethizon dorsatum—translates as “the animal with the irritating back.” While they appear prickly at all times, porcupines actually have a soft brown undercoat and coarser, longer guard hairs tipped with white that cover the quills. Fully grown, a porcupine weighs between 10 and 15 pounds and has 30,000 of these hollow, tapering, barb-tipped quills. Longest on the back and tail, the quills are raised when the porcupine senses danger, pushing the guard hairs forward to form an intimidating crest.
Approached by humans or other threatening animals, porcupines prefer to scurry away and climb a tree. Failing this, they will try hiding their faces and bellies—which have no quills—and presenting their backs. As a last resort, they release as many as several hundred quills by slapping an invader with their quill-studded tails. Embedded in flesh, the barbs will swell, driving the quills in deeper and making them difficult and extremely painful to remove.
No one seems surprised to learn that porcupines are mostly solitary animals. Near-sighted, slow-moving, they make their dens in rock ledges or hollow trees close to a good food supply. In our region, hemlock is a favorite food source and the mainstay of the porcupine’s winter diet. Although they don’t hibernate, porcupines curtail their activity and their range during the winter, never venturing far from their dens. Porcupine dens are easiest to spot in winter, when there will be large accumulations of scat around the entrances and hemlocks with partially stripped branches nearby.
The sedentary winter is the gestation period for the single porcupine offspring that will be born in April or May, its parents having enjoyed an extremely brief, if sweet, courtship in late October or early November. At the age of one or two, the female will go into heat for 8-12 hours, attracting the attention of males who follow her around, grunting and humming. Once she chooses her partner, the female engages in a kind of dance with him. Standing on their hind feet, the male and female embrace, placing their paws on each other’s shoulders and rubbing noses, whining and grunting all the while. They may cuff one another playfully before eventually falling to the ground, when the female obligingly flattens her quills and moves her tail out of the way. Once they have mated, the porcupines go their separate ways—despite their previous displays of affection.
Winter might be considered their “social season,” for porcupines are likely to group together in the choicest winter denning areas. Although they ignore each other, except for teeth-chattering over disputed food, as many as 100 porcupines have been found in large rock piles, and six were discovered living in an abandoned house in New Hampshire.
Believed to chew wood and leather for the salt left in it from perspiration, porcupines also need to hone their continuously growing teeth, which may explain why they gnaw at buildings. While tools can easily be stored out of a rodent’s reach, what about the damage porcupines do because of their appetite for the bark and buds of sugar maple, birch, white pine, hemlock, and fruit trees?
People can protect their orchards and plantations with electric fencing or by installing a 30-inch band of sheet metal or aluminum flashing around the base of individual trees. Liquid repellents available at hardware stores can also be brushed or sprayed on trees and buildings. If this seems like too much trouble, maybe it’s time for a change of attitude. As a biologist once told me when I complained about cluster flies, “You just have to appreciate biodiversity.”
Catherine Tudish is a freelance writer living in Strafford, Vermont.
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