Porcupine
Porcupine
The porcupine (Erethizon dorsatum) is second in size only to the beaver
among rodents of Alaska and has the northernmost range of all the world's
porcupines. There are few fossil remains of the porcupine and its immediate
ancestors, but evidence indicates that they have only been a part of
the North American fauna since three million years ago when they immigrated
north from South America. The porcupine is found throughout all of Alaska
except the Alaska Peninsula and Kodiak, Nunivak, and St. Lawrence islands.
General description:
This stout, short-legged mammal is 25 to 31 inches (73-78 cm) long and
is covered with hair and quills of varying length, except on the foot
pads and nose. 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 hair and a thick layer of body fat keep
the porcupine warm during the winter. The tail is club-like and the
upper surface is heavily covered with quills. The quilled pelage of
the porcupine makes it unique among mammals in Alaska. The 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.
The average weight of an adult male porcupine ranges from 15 to 18 pounds
(7-8.5 kg), but some individuals can weigh up to 25 pounds (11.4 kg).
Adult females weigh about 2 pounds (0.9 kg) less than the males.
The porcupine has excellent senses of smell, hearing, and taste, but
its eyesight is poor. Porcupines make a wide variety of sounds ranging
from whimpers to screams, depending upon the circumstance.
Life history: Breeding takes place in the fall months from September
to 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. Males use their incisor teeth and quills when fighting,
and usually it is the largest and heaviest male which wins dominance.
The breeding male then splashes the female with urine. If she is not
ready to mate, she shakes off the urine and leaves. If she is ready,
she stays and the male mounts in the traditional posture with the female
in front and the male in the rear. She will curl her tail over her back,
covering most of the quills. Males reach sexual maturity at 24 months
and females at 12 months.
After a gestation period of about 210 days, only a single young is born.
The gestation period is extremely long for a rodent, twice the time
for a beaver. At birth the young weighs between 1 and 2 pounds (0.5-1.0
kg) and is about 10 inches (25 cm) long. Its eyes are open and its body
covered with long grayish-black hairs and quills. Within a matter of
hours the quills dry and serve as protection. The young porcupine is
then capable of following its mother, although the young will not be
able to climb large trees for several weeks. The young are able to eat
some vegetation after a few weeks, but the female continues nursing
the young for 3.5 months. During the summer the young stay close to
their mothers, learning about den sites and food trees, but toward the
end of summer they start to spend more time apart. By October, when
the female mates again, the young are fully weaned and wander off to
face the winter alone.
Female porcupines are territorial and will exclude other females, but
males will overlap their home ranges. Females have approximately the
same size territories, but male home ranges vary according to age and
dominance with the largest males having the largest ranges.
During the winter, porcupines roost in their dens during the day and
during periods of cold weather. They use earth or rock caves, hollow
logs and trees, or even the thicker vegetation in a tree for dens. In
areas without snowfall, dens are not used so much. Porcupines stay active
throughout the winter. They feed during the night and during warmer
weather.
Porcupines are mainly nocturnal, although they can occasionally be seen
during the day. Since they roost and feed in trees, one would imagine
that they are accomplished tree climbers, but when observed they are
slow and awkward. Thirty percent of the animals examined in one study
showed evidence of healed fractures indicating that they had fallen
out of trees. When climbing, the porcupine uses the stiff bristles on
the undersurface of the tail as support. The animal has long, curved
front claws which also aid in climbing.
Food:
The inner bark (phloem and cambium layers) of spruce and hemlock are
the major winter foods for porcupine living in Alaska. In the spring
and summer, buds and young green leaves of birch, aspen, and willow
are eaten until the tannin levels build too high for the porcupine to
tolerate. Because they are vegetarians and most vegetable matter is
very low in sodium, porcupines need additional sodium in the blood to
balance cell potassium levels. As a result, porcupines seek out salt
sources such as natural licks, glue which bonds plywood together, human
perspiration on tools, road salt, and some paints. Porcupines also feed
on shed antlers and the bones of dead animals to obtain sodium.
Predation and defense:
Most carnivores would not pass up a meal of porcupine. However, an encounter
between a young inexperienced predator and a porcupine can be a very
painful experience. Some unfortunate carnivores have starved to death
because a mouthful of quills has prevented them from eating. In an effort
to remove the quills, the predator can cause the barbed quills to work
into the deep tissues. However, the quills are coated with a natural
antibiotic and rarely cause infection.
Predators have different means of killing and eating porcupines. The
fisher circles around the porcupine until it can bite its nose. After
repeated bites to the nose, the fisher then flips the porcupine over
to attack the quill-free belly. The porcupine is then eaten leaving
an empty quill-covered skin. This method may also be practiced by lynx,
wolves, coyotes, and wolverines which have been recorded eating porcupines
in Alaska.
When the porcupine is relaxed, the hair and quills lie flat and point
backwards. When threatened, the porcupine draws up the skin of the back
to expose quills facing all directions, and it then presents its formidable
bristling back. The porcupine tries to keep its back facing the attacker
and strikes back and forth with its tail. Although a porcupine cannot
throw its quills, the quills are readily dislodged when the tail is
shaken. This may give the impression that quills are being thrown. Recently
acquired quills can be easily pulled out of animals with a pair of pliers.
If a large number of quills are present or the have been allowed to
work in, the animal will have to be anesthetized in order to remove
them.
Conservation and management:
The porcupine can be easily approached and killed with a club because
of its plodding gait. This trait has saved the lives of hungry Natives,
trappers, and miners in times past. For this reason, although the hunting
season is open all year with no bag limit, many people do not kill porcupines
without cause. Some people find the meat too strong, but in some areas
of the state, porcupines with their heavy layer of fat are considered
a delicacy.
Quills sewn onto deerskin used to be the trading wampum of the Northeastern
Indian tribes. Quills are still used for decoration by the Athabaskans
of Interior Alaska. Natives used to kill porcupines just for their quills,
but today the Natives corner the animal and then tap the back of the
animal with a styrofoam paddle to collect all the quills they need.
The quills are dyed with locally obtainable vegetable materials and
then sewn into skin clothing, earrings, and artistic items.
Porcupines can be injurious to commercial forests and reforestation
projects by feeding on the terminal buds or eating the bark all the
way around the trees. When such problems occur, site specific control
may be necessary, although within most of Alaska porcupines are not
numerous enough to do much damage.
