North American Porcupine

North American Porcupine

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Description

The North American porcupine is second in size to the beaver among rodents in North America and has the northernmost range of all the world’s porcupines.  This stout, short-legged mammal is covered with hair and quills of varying length, except on the foot pads and nose and belly.  The tips of the long guard hairs are lighter and give the coat hues of yellow or white.  The hair on the belly is sparse and varies from black to brown.  The tail is extremely muscular and adapted to aid in climbing and defense.  The upper surface of the tail is heavily covered with quills, while the underside if covered in bristle hairs which aid in climbing.  The guard hair and a thick layer of fat keep the porcupine warm during the winter.

Lifestyle

In the Pacific Northwest, porcupines are primarily ground dwelling.  In eastern North America, they are mainly tree dwelling.  The amount of time they spend on the ground is directly related to the amount of ground cover that exists for foraging and predator protection.  Porcupines move slow, so they have a unique defense system against predators to make up for their lack of speed.  First, they climb trees to escape danger.  If this is not possible, they rely on their quills for protection along with chattering teeth and making whining sounds.  By tensing their muscles, porcupines can stand their quills up in a criss-crossed pattern which provides a solid layer of protection for all areas except for their bellies and faces (quills are very small on the face and absent on the belly).  Quills are modified hairs which have microscopic barbs on the tips and are filled with a spongy matrix.  Quills from different parts of the body vary in length, flexibility, color, shaft diameter and barb length.  Each adult has approximately 30,000 quills.   If a quill becomes lodged in the tissues of an attacker, the barbs pull the quill further into the tissues as the animal moves.  Predators have been known to die as a result of quill penetration and infection.  Porcupines have excellent senses of smell, hearing and taste, but poor eyesight.  They do not hibernate in winter, but will spend time in rock dens or covered areas to get out of severe weather.  Trees make good resting spots as well.  Trees are also the main food resource for porcupines during winter months in Alaska, when all leafy plants are dormant.  They have adaptations for life in and near trees such as long claws and textured foot pads to help with grip and climbing.  Porcupines climb large trees easily and may be found on small branches.  They also have a sensitive sense of touch, even able to detect items touched by the tips of their quills.  This helps in climbing trees and holding their position against tree trunks and branches, often using quills to support their weight as they lean.

Food Habits

The inner bark (phloem and cambium layers) of spruce, birch and hemlock along with spruce needles are the major winter food for porcupines in Alaska.  In spring and summer, buds and young leaves of birch, aspen, cottonwood and willow are eaten until the tannin levels build too high for porcupines to tolerate.  Because they are vegetarians and most vegetable matter is very low in sodium, they need additional sodium in their blood to balance cell potassium levels.  As a result, they seek out salt sources such as natural licks, glue which bonds plywood together, human perspiration on tools, road salt and some paints.  They feed on shed antlers and bones of dead animals for sodium and calcium.

Lifecycle

Breeding takes place from late September to early November.  Males seeking receptive females expand their home ranges up to five times the normal size.  If more than one male shows interest in the same female, they will fight for the opportunity to mate with the female.  After a gestation period of about 210 days, a single young is born.  At birth, they weigh between one and two pounds.  The eyes are open and they are covered with long grayish-black hairs and quills.  Within a matter of hours, the quills dry and serve as protection.  By October, when the female mates again, the young are fully weaned and wander off to face the winter alone.

Population Status, Threats & Conservation

Porcupine populations are stable in Alaska, and usually spread out enough to avoid lasting damage to trees by their bark eating habits.  They are eaten as a delicacy by Alaska Natives in many areas of the state, and their quills can by dyed and used in jewelry and decorations. 

Sources:
Weber, C. and P. Myers. 2004. "Erethizon dorsatum" (On-line), Animal Diversity Web
Alaska Department of Fish and Game, Porcupine notebook
San Diego Zoo, Porcupine fact page