Common Name: North American Porcupine
Also referred to as: Common Porcupine, Canadian Porcupine
Genus species: Erethizon dorsatum
Recognized subspecies: E.d. dorsatum, E.d. myops, E.d. nigrescens, E.d. bruneri, E.d. epixanthum, E.d. couesi, E.d. picinum
- The Porcupine is the second largest North American rodent next to the Beaver (Castor canadensis).
- Sexes similar in colouration and appearance; however, males may be significantly larger.
- Weight: Varies according to habitat. Males: 6 – 11.8 kg, females: 5.1 – 8.7 kg. Weights of up to 14 kg have been reported.
- Body Length: 60-90 cm (longer body lengths in males)
- Tail Length: 14.5 – 25 cm (longer tail lengths in males)
- North American Porcupines are easily recognized by their quills, which are distributed from head to tail on the dorsal portions of the body. These specialized hairs are an adaptation that decreases predatory encounters for this slow moving animal. Loosely embedded in the dermis, quills are easily dislodged and penetrate the flesh of a potential predator. Microscopic barbs on the tips of the quills serve to pull the quills deeper into tissue. Quill penetration can cause infection and in severe cases, the eventual death of an attacker. Adult quill sizes range from 2 – 10 cm. Larger Porcupines may have as much as 30,000 quills distributed throughout the body. Quills are not only used in defence, but also to warn potential predators of danger. When approached, Porcupines can erect their quills, creating the illusion of a much larger animal.
- Although large bodied, the North American Porcupine has short limbs with plantigrade foot structure. As such, Porcupines move slowly when walking, but are accomplished climbers. Long claws (4 on the forelimbs, 5 on the hindlimbs) increase traction while climbing and also assist in grasping food items.
- Porcupines across the majority of their distribution are dark in colouration, with whitish highlights produced by the white tips on the quills. In portions of their western range, Porcupines may have a yellowish appearance due to the yellow-gold colouration of the guard hairs.
- The dental formula is: I (1/1), C (0/0), PM (1/1), M (3/3) = 20 teeth.
- The continuously growing incisors are large and stained orange on the anterior surface. Alternate placement of enamel (anterior) and dentine (posterior) results in differential wear, creating a consistently sharp edge to the incisors.
- The large diastema between the incisors and the cheek teeth allow the lips to be closed posterior to the incisors. This permits gnawing while conserving body heat and moisture.
North American Distribution
Movements and Migratory Habits
Diet and Foraging Strategy
North American Distribution:
- Distribution of the North American Porcupine is widespread, including all of Canada south of the Arctic tree line (with the exception of Newfoundland), most of the western, northwestern and northeastern United States, and a portion of northeastern Mexico. Absent from a large portion of the Great Plains, coastal regions and southeastern United States; however, fossil evidence suggests these areas may once have been occupied by Porcupines.
- North American Porcupines are considered to be habitat generalists at the landscape level; however, selection patterns do appear at the home range levels.
- Extensively distributed across North America, Porcupines can be found in varied climates. Although primarily arboreal, Porcupines can also inhabit open landscapes such as desert shrub, tundra, and grassland habitats. The majority of their range, however, coincides with boreal forest regions.
- In forested regions, stands of deciduous trees, particularly those dominated by trembling aspen (Populus tremuloides) are selected as habitats. Strict coniferous stands and regions impacted by human activities are low in the selection hierarchy. Habitat use may shift, however, depending upon the density of Porcupines in the area, availability and age of tree species, predator density, and climatic conditions.
- In semi-arid regions, Porcupines select riparian habitats if available.
- Porcupines will often use existing cavities (rock piles, tree stumps, hollow trees, culverts) as dens. Den use may be extensive in the winter, but it also occurs in the summer months. Dens not only provide thermal functions, but also assist in predator and biting insect avoidance. Previous studies have noted individual variation in the use of dens. Some Porcupines occupy dens for large portions of a 24 hour period, whereas others may never use dens.
- Across their geographic range, Porcupine population densities vary substantially. Densities are habitat related; however, even in high quality habitats, population densities may drop significantly due to the presence of specialized predators, such as the Fisher (Martes pennanti).
- Porcupines maintain territories of varying sizes, with females upholding strong territorial boundaries, whereas the territories of males may overlap those of females and other males. Minimum annual female territory size is approximately 23 ha. Males tend to maintain larger territories (as large as 75 ha). It has been observed that male territory size positively correlates with mating success. Territory size may broaden or contract dependent upon habitat conditions and population density.
Movements and Migratory Habits:
- North American Porcupines are not generally migratory; however, they may undertake short distance movements between winter and summer habitats.
- Porcupines move further in summer and tend to restrict their movements in winter. Distances moved on an annual basis vary, dependent upon whether or not summer and winter habitat requirements are proximally interspersed.
- In forested regions, Porcupines spend the majority of their time in the trees foraging and resting. In regions lacking tree cover, Porcupines may be ground dwellers. The degree of ground dwelling is influenced by many factors. Nutritional needs, amount of ground cover, predator densities, and the availability of dens all factor in the determination of time spent on the ground. During bouts of terrestrial movement, human trails and roads are seldom used; however, they may function as corridors between habitat patches while foraging at night.
- Researchers have noted that Porcupines, although predominantly nocturnal, may increase diurnal activities at certain times of the year. Similar to den usage, diurnal activity is strongly linked to available ground cover, food sources, nutritional needs and predator densities.
- With the exception of the breeding season and portions of the winter, Porcupines are primarily solitary. Dens may be shared, dependent upon den availability (den sharing is inversely proportional to den availability). A solitary lifestyle is not common in strict herbivores that usually find safety in numbers (i.e., herds). The effective antipredator adaptations exhibited by Porcupines do not necessitate a social existence.
- Porcupines do not undertake hibernation. During the winter months, activity levels are limited to nightly foraging excursions. Stored energy reserves are heavily relied upon at this time.
- Recent evidence suggests that natal dispersal in this species may be female-biased, which may be motivated by inbreeding avoidance.
- Home ranges of Porcupines across their distribution are highly variable in size. Home range size is reported to relate to habitat quality; however, home range sizes for males may be larger in order to increase mating opportunities. Across both sexes, home range size may range from 15-85 ha, although smaller and larger home ranges have been reported.
Diet and Foraging Strategy:
- The Porcupine is considered a generalist herbivore at the species level, exhibiting selective herbivory at the individual level.
- Porcupines are mostly arboricolous–folivorous in the summer time, feeding on aquatic and terrestrial herbs, shrubs, fruits, leaves, and buds. Porcupines do not feed on tree species randomly; selection for certain species is evident. At the tree level, trembling aspen is selected over other deciduous tree species. Monotypic stands of preferred trees are chosen over heterogeneous stands. If fruit producing trees are available, these may be selected over aspen.
- Later in the season, in preparation for winter, they concentrate on hard and soft mast, such as acorns, seeds, fruit, and nuts if they are available.
- It has been reported that Porcupines may become less selective during the winter, with the diet consisting of twigs, buds, inner bark of trees (cambium), and evergreen leaves.
- Porcupines experience severe nutritional stress in the winter, as protein rich food sources are scarce. Weight losses of 17-31% in the winter have been reported. In late winter, Porcupines may leave the safety of trees to feed on protein rich grasses and riparian vegetation.
- Normal weights are restored by late summer. Mass gains of up to 40% of the spring weight have been noted.
- In habitats lacking sodium sources, Porcupines may exhibit a strong salt drive. Natural sources of sodium include aquatic vegetation and carrion. If these are not available, anthropogenic sources will be sought, such as residual road salt, treated or painted wood, rubber items, wooden furniture, axe handles and automobile tubing. The drive for salt seems to peak in April to May and again in August to September.
- Females become sexually mature as yearlings, although breeding usually does not occur until the second year of life.
- North American Porcupines are polygynous. Females are seasonally polyestrous with estrus cycles reoccurring every 25-30 days if fertilization does not occur. Upon copulation/fertilization, a mucous plug forms in the vagina and females become nonreceptive.
- Agonistic encounters between males are common during the breeding season when multiple males discover receptive females.
- Males may spray urine at females, presumably to accelerate estrus.
- Porcupines generally mate in the late fall or early winter. Gestation is nearly 7 months. Parturition usually takes place in April through May. They give birth to a single litter of one pup; instances of twins have been reported.
- Average weight of the young at birth is 450 gm. The pups are precocial; they are born fully quilled and open eyed, and are able to climb shortly after birth. Weaning may not occur until the fall; however, pups are able to survive on a diet of vegetation by 2 weeks of age.
- Provincial Status: Secure
- Federal Status: Not at risk
- Although porcupines exhibit well developed antipredator morphology, they are still subject to predation. Quills have been found embedded in Coyotes (Canis latrans), foxes (Vulpes spp.), wolves (Canis lupus), Cougars (Puma concolor), Bobcats (Lynx rufus), Lynx (Lynx canadensis), and bears (Ursidae spp.), in addition to Great Horned Owls (Bubo virginianus).
- Predators kill a porcupine by attacking unprotected portions of the body, such as the face or ventral region. Foraging animals seem to accept an increased risk of predation, whereas sleeping or resting animals avoid high risk by using tall trees or dens. Risk acceptance, therefore, seems to be linked with nutrient/energy requirements. Fishers are a primary predator of Porcupines. There is some evidence to suggest that trapping of Fishers may be responsible for population expansions and high densities in certain habitats.
North American Porcupine photo © 2006 Dan Bannister. Retrieved from www.istockphoto.com/stock-photo-2512875-porcupine.php on 22/09/09. Used with permission.
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