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Porcupine
(Erethizon dorsatum Linnaeus)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry. 216pp.

Family: Erethizontidae

Description: As many as 30,000 needle-sharp quills cover the upper parts of the porcupine’s body and tail. These hollow, barbed quills, actually derived from hairs and modified for defense, attach loosely to the skin. A porcupine cannot throw its quills, but can erect them, and the quills detach easily, penetrating the skin of any animal touching this large rodent. The thick muscular tail can drive the quills into an opponent, and it is a formidable weapon when flailed suddenly. If the tail strikes a hard object such as a rock, quills may be dislodged and fly through the air, one likely origin of the quill throwing myth. The mechanical action of the barbules in moving muscles draws a quill deeper into the tissue of an opponent, where it may produce fatal injuries by puncturing major blood vessels or vital organs.

A stout, compact body, small head, dull black eyes, short ears and course brown to black fur tipped with white, are additional characters of the porcupine, also known as the quill pig. Prop-like bristles on the undersurface of the tail function as a brace for climbing. Roughened foot pads, and strong, curved, claws are other climbing aids. Adults are 64-102 cm (25-40 in) in length, and weigh 4.5-9.1 kg (10-20 lbs), occasionally 18 kg (40 lbs).

Range and Habitat: The range is most of Canada, Alaska, northern Mexico, and the western and northern U.S. The porcupine is a common and wide-spread resident of the Adirondacks where it occurs to elevations of at least 1220 m (4000 ft). It prefers mixed forests. Dens are in hollow trees, stumps, and logs; under large rocks and the roots of overturned trees; within caves, rocky ledges or crevices, and abandoned buildings. Accumulations of droppings are evident in and around dens.

Food and Feeding Behavior: The herbivorous porcupine specializes in a winter diet of the inner bark of trees which has earned it the wrath of forest managers. However, the porcupine’s economic impact as a whole is equivocal, ranging from extensive in localized areas to negligible in others. Overall, porcupines cause less forest damage than fires, winds, disease, and insects.

Adaptations equipping the porcupine for a woody diet include incisors hardened by orange salts and growing 30 cm (12 in) per year; enamel-surfaced cheek-teeth powered by strong jaw muscles that pulverize woody tissue; a digestive system that fills 75% of the body cavity; and a cecum containing a symbiotic microflora that breaks down cellulose.

Ten species of trees provide much of the winter diet. Each porcupine usually restricts its feeding to 1-2 species, perhaps because of the role of its microflora. Hemlock cambium, phloem, and foliage are the preferred foods. White pine, red spruce, larch, sugar maple, yellow birch, and beech are some of the other key species. A porcupine ingests about 430 g (0.9 lb) of food each day, but in spite of the bulk, a lack of nitrogen may cause starvation, and most individuals lose about 17% of their total weight during the winter.

Protein-rich leaf blades by “nip-twigging”, form the spring diet. As trees develop toxic tannins, porcupines select species such as aspens with less tannin, and herbaceous plants. The summer diet of foliage, rich in potassium, causes an excessive excretion of sodium; thus forcing porcupines to seek salt. This may come from aquatic plants such as the water lily, but also from tires, break lines, plywood, and toolhandles which the porcupine gnaws. Beechnuts, fruits, and acorns are alternative summer and autumn foods.

Activity and Movement: The semi-arboreal porcupine does not hibernate. During the winter it travels from the den to a nearby tree to feed, sometimes visiting the same tree for days or weeks, and reaching it following a well-worn trail over the snow. To reach its food, a porcupine climbs trunks and large branches, and propped in place with its tail, hind feet grasping the bark, uses the forefeet to gather twigs and foliage, or to clasp the trunk while gnawing bark. Pieces of bark, twigs, droppings, and in the case of conifers, needles, litter the snow beneath a tree in which a porcupine forages. It descends by backing down trunks Falling out of trees, (relatively common in porcupines) often results in bone fractures which heal quickly.

Porcupines are mainly active at night. They can swim but rarely enter water, and then only to gather aquatic plants which they carry to shore to eat The typical gait on land is an awkward waddle, but porcupines can run short distances. Intruders elicit quill-raising and tail-thrashing. A porcupine defends itself by trusting the vulnerable head into a root crevice, or beneath a log or rock, but when approached in the open, constantly shifts its position to orient the back and tail toward a potential source of danger.

Reproduction: Porcupines court and mate in November and December. After a 205-217 day gestation period, females bear a single youth, rarely two, in a den lined with branches and roots. At birth, the precocious young weighs about 454 g (1 lb), the eyes are open, incisors and some molars fully erupted, and the quills soft but hardening within an hour. Although weaning does not usually occur until 3 months of age, a young porcupine can survive on vegetation at 14 days. By 6 months of age, it is independent. Porcupines begin breeding at 15-18 months. The potential life span is 10 years.

Predators: Many animals occasionally kill porcupines, especially young ones. These include the coyote, red fox, black bear, bobcat, mink, marten, long-tailed weasel, ermine, and great horned owl. The fisher is the only habitual predator of the porcupine, and may suppress populations of this rodent. Predators sometimes succumb to quills.

Social Behavior:

  • Social system - Porcupines are solitary during much of their lives. Exceptions occur during the winter when as many as 12 may den communally, and during courtship. Several males may approach and compete for the same estrous female, the competition resulting in wounds from biting and quill impaction. Pair bonds are brief or absent. Winter home ranges are 2.4-4.8 ha (6-12 acre); summer ranges are larger, usually 10-14 ha (25-35 acre). Porcupines are not territorial, although an individual may drive others from a tree in which it is feeding during the winter. Home ranges may overlap, but densities vary considerably within suitable habitat, averaging one porcupine per 10-20 ha (25-50 acre). 
  • Communication - Porcupines are near sighted, but have acute hearing and a keen sense of smell. The vocal repertoire is extensive, and includes tooth-chattering, low-pitched grunts, screeches, snarls, and high-pitched cat like shrieks. Scent marking is prevalent, e.g. males seek and urinate on urine deposits made by estrous females. During courtship bouts, a male sprays a receptive female with bursts of urine before mating with her.

Additional References

Roze, U.  1984. Winter foraging by individual porcupines. Canadian Journal of Zoology, 62:2425-2428.

Shapiro, F. 1949. Ecological and life history notes on the porcupine in the Adirondacks. Journal of Mammalogy, 30:247-257.

Woods, C. A. 1973. Erethizon dorsatum. Mammalian Species, 29, 6pp.

Order: Rodentia