North American Porcupine
The North American Porcupine (Erethizon dorsatum,) is the largest species of porcupine and the only one that can be found in the United States and Canada. Within their range, they are the second largest species of rodent, aside from the beaver. Although not an aggressive animal, porcupines are equipped with a coat of sharp defensive quills that makes them easily identifiable. This species faces no risk and enjoys an extensive geographic range.
The North American Porcupine is easily identifiable by their stout lumbering bodies and spiny coats. NAP’s reach a mature length of 33” to 46” (the tail comprises approximately 1/3 of that length.) Adults weigh between 12 to 35 lbs. (males tend to be the larger sex.)1 NAP’s have small ears, small heads, and large front teeth that aid in consuming wood. There is a prominent diastema between the front teeth that allows them to draw in their lips while gnawing. Their skulls exhibit a lack of canines. Like other hystricomorphs, they have unique chewing muscles.
The name porcupine is derived from the Latin for “quill pig.” Their coats are comprised of three types of hair: a soft, dense woolly undercoat, long, course, brownish-yellow to black guard hairs, and quills. There are 24 species of porcupines that have coats made of more than 30,000 quills that act as sharp defense mechanisms. These tubular quills are filled with a spongy matrix (making them rigid but light,)2 and cover a porcupine’s head, back, sides and tail. The longest quills are found on the rear and may be up to 12” long, while the shortest quills are on the cheeks.3 The quills located within a central black line on their lower backs and tails are accented with white. This contrast appears on porcupines by three months old and acts as a preliminary warning to approaching predators (many being color blind.)4 Porcupines are non-aggressive mammals that only attack if they are unable to escape a threat. Typically, their quills lay flat but in defense, these quills become erect to fend-off predators. If an attack occurs, the porcupine lashes out at the predator, and the quills detach from the porcupine’s body (despite popular belief, porcupines cannot throw their quills.) The quills have sharp tips and barbs that embed into the predator’s body. The predator’s body heat causes the barbs to expand and muscle movements push the quills further into the predator’s skin. Embedded quills may cause infection or death.5 Growing new quills is possible but difficult for porcupines. To avoid losing quills, porcupines exhibit several warning behaviors to fend off predators before an attack ensues. These include visual cues (contrasting warning colors and erected quills,) acoustic clues (teeth chattering,) and chemical clues (porcupine’s emit a strong chemical odor when threatened.)
Porcupines are well suited for climbing and spend much of their time in trees. Different trees are chosen for feeding and resting. Their feet feature specific adaptations that allow them to grip surfaces and brace themselves high off the ground. They have four long claws on their front feet in addition to a vestigial thumb, and five long claws on the back feet. The palms and soles of their feet are hairless and have pebbly surfaces that create friction with surfaces. Porcupines often secure themselves when climbing with their hind feet and grasp food with their front feet. The quills are also useful climbing implements. Quills located on the tail are thrust into the tree to help stabilize the porcupine and prevent downward sliding. Porcupines are known to spend the majority of time in trees; however, this behavior is directly related to the amount of ground cover available and the types of predators within a habitat. If appropriate ground cover exists, a porcupine will tend to forage and take cover on the ground more often. NAP’s are also good swimmers, aided by their lightweight quills that help keep them afloat.
They are solitary animals but are known to den and forage with other porcupines during the winter, most likely for protection from predators. These groups do not tend to reflect mating preferences. They build their dens in hollow trees, rock piles or caves. These dens are not used for hibernation, rather sporadically throughout the winter during severe weather.
Both males and females establish and defend territories. Males establish territories that overlap those of several females, but never that of another dominant male. Females’ territories tend to be consistent in size but the size of a male’s territory reflects his age and dominance. Juvenile males settle and establish their initial territories within their birth territories. As males mature, their territories increase in size. Juvenile females part from their birth territories and establish new territories before they reach maturity.6
Porcupines use several methods of communication with other members of their species and with predators. They are vocal animals, creating sounds that include moans, grunts, coughs, wails, whines, shrieks and tooth chattering (used to warn predators.)7 NAP’s also emit chemical signals and display the white/black markings on their quills when confronted by a threat. Their padded palms and soles provide them with a keen sense of touch.
Porcupines in the wild may live up to 18 years. It has been observed that a porcupine’s life expectancy is proportionate to the health and longevity of their grinding teeth. By 12 years of age, these teeth begin to show wear, resulting in a diminished diet and, therefore, a diminished body mass.
NAP’s have adapted to many types of climates due to their extensive range that includes a variety of elevations and geographic locations. They may be found living in coniferous or deciduous forests, savannahs, grasslands, mountains, or open tundra. Their behaviors are impacted by their habitat. In the Pacific Northwest, porcupines tend to be more ground dwelling, while populations in New York are primarily arboreal.
Within their habitats, porcupines have many predators, despite their weaponry. These include bobcats, coyotes, wolves, lynx, mountain lions, fishers, wolverines, and birds of prey. These predators have adapted to the porcupine’s weaponry, attacking from the front and flipping the porcupine over exposing its vulnerable stomach.
The NAP has the most northern geographic range of all porcupine species. Their range includes most of North America, spanning from the Arctic Ocean to northern parts of Mexico.
Porcupines have herbivorous diets that vary seasonally. During the spring and summer, their feeding rates decrease due to the increased availability of and their preference for high protein foods. Their diets include leaves, clover, twigs, bark, grasses, flowering herbs, and fruit (especially apples.) The herbivorous nature of their diets affects their sodium metabolism, causing porcupines to crave salt. As a result, they are driven to chew on wooden implements, structures, vehicles, and other items with residual salt. They are generally nocturnal foragers.
They breed once a year, between late summer and early fall. Females secrete chemicals, make high-pitched vocalizations, and mark with urine to alert males of their 8 to 12 hour estrous period that occurs prior to ovulation. Sexually mature males fight to establish sexual dominance, using loud vocalizations, biting, and erect quills. The dominant, and often largest, male establishes a breeding territory (which he may use for up to three seasons,) and wins breeding rights (and must defend the pre-estrous female for 1 to 4 days until copulation.) The dominant male performs a peculiar mating dance, which includes spraying the female’s head with urine. This display will continue until the female becomes receptive to the dance and mating. A male may mate with several consenting females.
Copulation takes place on the ground and may last for several hours. Mating ends when a vaginal plug is formed by an enzymatic action that occurs in the semen. The plug prevents other males from mating with the female.
After a gestational period of 210 days, the female gives birth to a single baby. The newborn has soft quills (which harden an hour after birth,) and weighs between .9 to 1.2 lbs.
The mother nurses her young for approximately 130 days, although young porcupines can eat solid food within a few days of birth. For the first 6 weeks, the baby remains close to its mother. The female sleeps and feeds in trees during the day (leaving her baby hidden on the ground nearby,) and returns to her baby at night.
By six weeks old, the baby begins following its mother to feeding trees, remaining at the base while she feeds. Over the next few months, the distance between the mother and her offspring increases during foraging trips and by 5 months old, the juvenile is independent (left by its mother to survive alone during the upcoming winter.)
Female reach sexual maturity by 25 months old. Males do not reach sexual maturity until 29 months old.
Notes of Interest
While quills are obviously dangerous for predators, they pose some risk to porcupines as well. Porcupines can fall out of trees, resulting in self-impalement. Additionally, the force it takes to impale a predator with quills might exceed the weight of the porcupine, resulting in a difficult or impossible separation of quills from the porcupine.
Native Americans once revered the porcupine for its meat and quills (which were used as decoration and to establish status.)
NAP’s are considered a pest by the timber industry. Their tendency to feed on bark and twigs leaves trees stunted or deformed and unsuitable to be turned into lumber.8
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