Porcupines use a combination of acoustic, chemical, visual, and tactile communication. Females communicate their readiness to mate by vaginal secretions, urine marking, and high pitched vocalizations. When threatened, a porcupine will chatter its teeth and produce a chemical odor, intended to warn off any predator. Males compete using fierce vocalizations. Visually, the porcupine communicates the presents of its weaponry by displaying the white on black markings on its back and tail. Tactile communication occurs when physical aggression erupts, as well as between mates, and between mothers and their young.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones ; scent marks
Perception Channels: visual ; tactile ; acoustic ; chemical
This species is not a special conservation concern.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Porcupines have two areas of conflict with humans. Their salt cravings often lead them to chew on housing structures, automobiles, and anything made of plywood or with salt residue (usually from road de-icing salt). They also have a negative impact on the timber industry. Trees that have been fed on by porcupines tend to have stunted growth and twisted evil looking crowns, usually making the tree unsuitable for use as lumber.
Negative Impacts: crop pest; household pest
Porcupines were once revered by Native American cultures throughout the continent as a food source, a source of quills for decoration, and legendary status. Today, however, they are mostly considered a pest. Bounties, large poisoning efforts and unregulated killing have only recently been discontinued. Some would argue that porcupines’ inherent value is the ease and accessibility of the species to research and study.
Positive Impacts: research and education
Porcupines of the Rocky Mountains prefer habitats on rocky, south facing slopes. This brings them into contact with wood ticks that share the same habitat. Wood ticks, Dermacentor andersoni, are the host of Colorado Tick Fever virus; however porcupines do little to spread this virus. This is because only adult ticks attach to porcupines, and adult ticks do not spread the virus. In one study, 18 porcupines yielded a total of 448 ticks.
Porcupines can generate stress on their environment, although their overall detrimental effect is usually largely over-emphasized (usually focused on their intrepid salt excursions). One example of porcupines adding a stress to their environment is in Texas, where they feed largely upon the bark of pinyon pines. It has been suggested that because of porcupine foraging, these trees have been made more vulnerable to the infestation of bark beetles.
Several factors have led to stresses on porcupine populations. In the Great Basin, near extinction of a population of porcupines was discovered to be a direct result of increased mountain lion predation. Increased predation may have been a result of low mule deer populations in the area. Increased predation on porcupines can also be a consequence of predator shifting when snowshoe hare numbers decline. Increased stress from natural predators signifies the fragile dynamics between porcupines and their environment. Historical studies have indicated a very cyclical fluctuation in populations of porcupines.
In northern Michigan, Fishers Martes pennanti were reintroduced to limit the porcupine population growth and nearly eliminated the species from the area. Limited den sites (standing hollow snags), brought about by logging practices, increased porcupine exposure to fishers. In the northeast, where hemlock plays a major role in porcupine winter foraging, pests such as the hemlock wooly adelgid, Adelges tsugae, along with increased hemlock logging may pose problems for future porcupine habitat.
Porcupines are generalist herbivores. Diets vary throughout the year in response to minute changes in plant chemistry. Feeding rates also change seasonally. Throughout the spring and summer months, when high protein foods are readily available, feeding rates are reduced. However, in the autumn, feeding rates increase, probably in preparation for the winter scarcity of high quality forage.
Although typically a generalist, research has shown some selectivity between plants with higher nutrient content. However the amount of selectivity does not approach that shown by other specialized herbivores.
Selectivity varies between populations, with porcupines in some habitats showing more selectivity. Porcupines in the Rocky Mountains feed exclusively on ponderosa pine phloem, probably because this species dominates the ecosystem. Porcupines in eastern deciduous forests, however, feed on a number of different species of trees. In Massachussettes, porcupines were found rarely to feed on bark, whereas in Texas they forage largely on bark.
The crucial nutritional resource for porcupines is nitrogen. Winter sources of nitrogen include bark, twigs, and evergreen needles. These are relatively poor sources of nitrogen, so porcupines move continuously towards starvation, constantly loosing weight throughout the winter.
Porcupines are able to forage on low nitrogen, high fiber foods because of their unique ability to retain nitrogen from their food. This is done by reducing fecal nitrogen losses. The ability of porcupines to digest very high fiber foods better than some hindgut fermenters and ruminants may be due to the extended time food matter stays in the digestive system.
Dietary patterns of porcupines have been extensively studied in eastern deciduous forests. In the spring, they focus their feeding energy on the buds of sugar maple trees, a rich source of protein. As soon as the leaves flush out, the sugar maple is abandoned because leaves contain high amounts of tannins (chemicals toxic to porcupines). Porcupines move on to the cambium of basswood, aspen, and sapling beech trees. Understory beech trees contain much less tannin than adult trees, a trait a porcupine can easily ascertain. Aspen catkins are utilized for their high level of protein. Also ashes are fed upon heavily, because they are relatively easy to climb (compared to the smooth bark of beeches), and because they have relatively low tannin levels. Fall feeding abruptly changes when oak acorns and beech nuts become available. Porcupines feed on these nutrient packed meals before they have fallen to the ground. However, after the nuts have fallen, porcupines are out-competed by deer and squirrels. Mast years in nut producing trees have a direct effect on these herbivores. Winter foraging is focused on the phloem of hemlock, sugar maple, primarily within the canopy of these stands.
Other foods utilized by porcupines include raspberry stems, grasses, flowering herbs, and a large amount of apples. Herbivory has an effect on the sodium metabolism of porcupines, which results in a lust for salt. Porcupines will chew on the wooden handles of human tools, other human-made wood structures, and areas of collected roadside salt runoff.
Porcupine feeding happens primarily at night. This is related to changes in plant and leaf chemistry at night. Porcupines take advantage of the added nutrients available during the night-time metabolic processes of plants.
Plant Foods: leaves; roots and tubers; wood, bark, or stems; seeds, grains, and nuts; fruit; flowers
Primary Diet: herbivore (Granivore , Lignivore)
North American porcupines, Erethizon dorsatum, have the northern most range of all porcupines. They inhabit much of North America between the Arctic Ocean and northern Mexico. Porcupines are found throughout most of Alaska and Canada, in the northern part of the Great Lakes region, all throughout the west and northeast regions of the United States. Populations have been studied extensively in the eastern deciduous forests of New York and Massachusetts, the Great Basin Desert, and the woodlands of Texas.
Biogeographic Regions: nearctic (Native )
Erethizon dorsatum uses a broad variety of habitats. With an extensive range, porcupines can be found in varied climates, and at varied elevations. Porcupines live in open tundra, deciduous forests, and desert chaparral. Porcupine habitat varies geographically. In the Pacific Northwest, these animals are primarily ground dwelling. In New York, porcupines are mainly tree dwellers. In Massachusetts, they spend 13% of their time on the ground. The time porcupines spend on the ground is related to the amount of ground cover that exists for foraging and protection from predators. In places of deer overpopulation, ground cover can be scarce, thus keeping porcupines in the trees. Density of predators also determines time spent on the ground, because most porcupine predators are non-arboreal species. Porcupines will spend winter in dens, usually rock dens where available. When ground dens are not available, porcupines choose trees to rest in. Different trees are chosen for resting than for feeding. In eastern habitats, hemlocks are usually chosen over other conifers for both resting and feeding. These trees have superior thermal protection, sight protection (hemlocks have thick foliage), are stronger, and have higher nutritional value.
Southern populations of porcupines exhibit no seasonal use of trees. In southwestern Texas, porcupine populations both rest and feed in papershell pinyon pines (Pinus remota), as well as in oaks and other hardwood species. Porcupines in the Rocky Mountains feed primarily on ponderosa pines, and rest in dens on the ground. Similarly, porcupines in the Great Basin have been observed to use dens in rock outcroppings and juniper trees for cover during the winter. They travel between dens and small riparian areas to forage on tree bark, making them susceptible to predators.
Habitat Regions: temperate ; polar ; terrestrial
Terrestrial Biomes: tundra ; taiga ; desert or dune ; savanna or grassland ; chaparral ; forest ; scrub forest ; mountains
Porcupines are relatively long-lived animals that can live up to 18 years in the wild. Porcupine longevity is probably limited by the life of their grinding teeth. Porcupines over 12 years show diminished feeding and are usually smaller in size.
Range lifespan
Status: wild: 18 (high) years.
Average lifespan
Status: wild: 6 years.
Average lifespan
Status: wild: 17.0 years.
Average lifespan
Status: wild: 18.0 years.
Erethizon dorsatum is the second largest rodent in North America, outsized only by beavers. Individuals range in length from 600 to 900 mm, and weigh between 5 and 14 kg.
It is distinguished by its stout, slow, lumbering form and by its spiny coat. On the whole, porcupines appear dark brown to black, with dorsal guard hairs and spines that contain bands of yellow. Spines called quills extend from head to tail on the dorsal surface. The middle of the tail and lower back are marked by a black line. Quills on the black area are fringed with white. Because porcupines are nocturnal, the white on black markings stand out, alerting their mostly color blind nocturnal predators of the danger they present. This pattern is visible after porcupines are three months old.
Porcupine quills have microscopic barbs on the tip. They are usually around 75 mm long and 2 mm wide. Each animal has approximately 30,000 quills. If a quill becomes lodged in the tissues of a would-be attacker, the barbs act to pull the quill further into the tissues with the normal muscle movements of the attacker, moving up to several millimeters in a day. Predators have been known to die as a result of quill penetration and infection.
Skull characteristics include a lack of canine teeth and a dental pattern of 1/1, 0/0, 1/1, 3/3. The prominent diastema allows the lips to be drawn in while gnawing. Like other hystricomorphs, porcupines have unique chewing muscles. Efficient chewing movements are made possible by an arm of the masseter muscle, which passes through the infraorbital foramen.
Like the porcupines found in Central and South America, North American porcupines have arboreal adaptations including long claws (four in front with a vestigial thumb, and five in back). These claws, along with rather unique palms, allow for unproblematic navigation in trees. Porcupines can easily climb large trunks and surprisingly minute branches. The palms and soles of porcupines are naked with a pebbly surface. This texture increases the surface area and thus the friction while in contact with a branch. Associated with this adaptation, porcupines have a keenly developed sense of touch. This further aids them in their nocturnal navigation. It also allows porcupines to secure themselves in trees with their hind feet while manipulating food with their front appendages. Finally, the quills of porcupines prevent downward sliding while animals are grasping trees with their hind feet. The quills on the tail are used to stab the tree, further increasing fiction and stabilizing the animal in the tree.
A characteristic unique to E. dorsatum, compared to its Central and South American relatives, is adaptation to cold. No other hystricomorphs can withstand such high variance in temperature as North American porcupines can tolerate.
North American porcupines are sexually dimorphic, with males being larger than females. The size dimorphism is explained proximately by the faster growth rates and longer periods of growth which males experience relative to females. Because males with larger size have higher reproductive success than do smaller males, sexual selection promotes increased male size in this species.
Range mass: 5.000 to 14.000 kg.
Range length: 600 to 900 mm.
Sexual Dimorphism: male larger
Other Physical Features: endothermic ; bilateral symmetry
Average basal metabolic rate: 13.675 W.
Porcupines possess a very unique defense system. A porcupine’s first line of defense is escaping from danger by climbing up a tree. However, if such an escape is not possible, the porcupine has many options. Porcupines are the only mammal in North America to use quills to deter predators. Around 30,000 quills are present on the dorsal side of a porcupine. Because loosing quills is very expensive to a porcupine, these animals have developed several warning signs to precede their use of their ultimate weapon.
First are the aposematic colorations on the animal. The white-tipped quills on a black band on the tail and back stand out, and warn possible assailants of danger. Second, porcupines emit an auditory warning: a quiet clattering of the teeth. If both visual and accoustic warnings fail, a porcupine will erect its quills, and simultaneously release a nasty scent. Quills are only used if the threat has not been deterred by these other means.
Porcupines use their quills in two ways, defensively (as a shield made of barbs) and offensively (when they are driven into the predator). Upon contact, the porcupine needs to quickly separate from the quills, and thus separate from the enemy, so they have evolved unique quill-release systems. Erect quills release easier from the porcupine after the quill has been pushed into the would-be assailant's body. The force is supplied by the contact with the would-be predator. Relaxed quills show no difference in release energy required.
Quills have a design that promotes their movement deeper into a predator once they have been embedded. The quills are not hollow, but are filled with a spongy matrix, which makes them very rigid and light.
Quills present some dangers to porcupines. Falling out of trees is quite common for porcupines, and self-impalement is definitely a hazard. Also, the force needed to remove the quills from the porcupine, after they are embedded in the assailant, may be larger than the weight of the porcupine, so separating may be problematic.
Even with this elaborate defense mechanism, porcupines are preyed upon by a couple of co-adapted predators. Several predators exist that at least have been known to kill a porcupine. The list includes lynx, bobcats, coyotes, wolves, wolverines, and great horned owls. Important predators include mountain lions and fishers Fishers will attack from the front repeatedly, avoiding the tail quills, until they are able to flip a porcupine on its back and attack the unprotected ventral surface. Mountain lions supposedly make no attempt to avoid the quills of porcupines; instead they attack at will and deal with the consequences. Predators tend to hunt and kill porcupines mostly in open habitats.
Known Predators:
Anti-predator Adaptations: aposematic
The mating system of E. dorsatum is considered female defense polygyny. Males defend a pre-estrous female from 1 to 4 days prior to copulation. Porcupines breed only once a year. Female porcupines advertise their 8 to 12 hour estrous period well ahead of time through vaginal secretions, urine marking, and high pitched vocalizations. In doing this, females attract many males who compete with each other to determine dominance. A dominant male breeds with a number of different females, but only when the females are willing. This ensures that the "best" male fathers a female's offspring.
Females maintain a territory, and defend it against other females; however male territories typically overlap those of several females. The territories of dominant males rarely overlap. Females all maintain similar sized territories, but male territory size varies with age and dominance status. Juvenile males settle as permanent residents in their natal area. They have smaller territories than do adults, but expand their territory size as they mature. Females disperse from their natal area before reaching maturity.
Male/female pairs sometimes share winter dens, although this den sharing is not exclusive to mated pairs. Den sharing is not necessarily considered part of the mating system of porcupines.
Mating System: polygynous
Females advertise their readiness to mate by vaginal secretions, urine marking, and high pitched vocalizations, well before the time of ovulation. This means that several males converging on an advertising female will have to compete for, and then defend, the female. Mating will only happen after a female has chosen a male and is receptive to him.
Males compete with each other using loud vocalizations, violent biting, and each uses his quills as weapons. Although the competition happens in trees, mating exclusively happens on the ground. The pair will mate for several hours until a vaginal plug is formed, which then stops the copulation, and prevents further copulation with other males. This plug is formed by enzymatic action in the semen.
Male porcupines display a strange courtship ritual, which involves dousing of the female with his urine. The urine showers are continued until the female is receptive to both the shower and the male. According to Roze (1989), "Everything suggests the urine is fired by ejaculation, not released by normal bladder pressure. Porcupines with everyday full bladders don't squirt their urine, don't have erections, and don't aim at females."
Breeding occurs in October and November. Gestation in this species is 210 days, after which a female gives birth to a single offspring. Newborns weigh between 400 and 530 g. Young are nursed for about 127 days. They become independent of their mothers at approximately 5 months of age, but are not sexual mature until the age of 25 months for females, and 29 months for males.
Breeding interval: North American porcupines breed only once a year.
Breeding season: Mating occurs in the months of October and November.
Range number of offspring: 1 to 2.
Average number of offspring: 1.
Range gestation period: 205 to 217 days.
Average gestation period: 210.25 days.
Range weaning age: 127 (low) days.
Range time to independence: 5 (low) months.
Range age at sexual or reproductive maturity (female): 25 (low) months.
Range age at sexual or reproductive maturity (male): 29 (low) months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; induced ovulation ; fertilization ; viviparous
Average birth mass: 500 g.
Average number of offspring: 1.
Parental care is provided by the mother. Mainy, a mother provides her baby with food. For the first six weeks of a porcupine's life, its mother is always close by. They meet only at night. During the day the baby is hidden on the ground, while the mother sleeps in the trees. After six weeks, the baby porcupine follows the mother to feeding trees and waits for her at the bottom. Over the next couple months, resting positions and foraging distances show increasing separation between the young porcupine and its mother. The mother continues to travel to the position of the baby every night, following landmarks and not scent trails back to the infant. By mid-October the baby completely loses contact with the mother and is left to survive its first winter alone. The father spends no energy in the rearing of or caring for the offspring. Males have little to no contact with their offspring.
Parental Investment: no parental involvement; precocial ; female parental care ; pre-fertilization (Protecting: Male, Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
