Posts tagged “Erethizon dorsatum”

Porcupines possess roughly 30,000 quills — hollow, modified hairs which are made from the same material (keratin) as feathers,claws, scales, hairs and fingernails.  They cannot “shoot” their quills anymore than we can shoot our hair, but their subcutaneous muscles can cause the quills to become erect as well as loosen them so that when touched, the quills are easily released.  Each quill possesses between 700 and 800 barbs along the four millimeters or so nearest its tip.  It is these barbs that help a quill remain embedded in the tissue of a predator. 

Researchers have found that barbed quills penetrate deeper into muscle than quills without barbs, and require half the penetration force.  They have been found to be four times harder to pull out than barbless quills.  It has been suggested that the barbs ease the quill’s penetration by concentrating force along the edges of the barbs, similar to how the serrations on a knife blade make cutting meat easier. 

Fortunately for porcupines, their quills are covered with a natural antibiotic which protects a porcupine from infection should it be impaled by one of its own quills or one from another porcupine. ( Photo: porcupine with quills from another porcupine embedded in nose)

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Porcupines are forced to exert a lot of effort if they are in need of food and the snow is deep.  Unlike many rodents that are light enough to travel on top of the snow, Porcupines must plow their way through it.  Their weight, short legs, and bare footpads make traveling in snow challenging, to say the least. 

If the snow is deep, the winter ranges of Porcupines are considerably smaller (18 acres in one research study) than their summer ranges (160 acres in same study).  Because of the energy needed to travel through the snow, Porcupines usually feed just a short distance from their winter dens, more often than not within 200 feet.  Their feeding trails from rocky or hollow tree dens to their woody food sources (often Eastern Hemlock-note bits of branches on snow in photo, American Beech and Sugar Maple), are very distinctive.  They are used every night when Porcupines leave their dens to feed and again several hours later when they return.  These trails become well marked with urine, and less frequently with scat and quills. ( Photo insert: Porcupine rock den entrance)

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Coyote tracks from several directions coalesced in a spot where the frozen skin of a porcupine lay.  There was not one morsel of flesh, and next to no bone, left inside the skin, which had partially been turned inside out.  Inspection of the porcupine’s head confirmed the likelihood that coyotes were responsible, as fishers, notable porcupine predators, kill their prey by repeatedly attacking a porcupine’s head, and the head of this porcupine was unscathed (see insert).  The only other possible predators would be a bobcat or a great horned owl, and there were no signs of either present.  While it is possible that the porcupine died a natural death and opportunistic coyotes took advantage of an easy meal, it appeared to be in good condition, and thus it is equally or more likely that coyotes succeeded in gaining access to the porcupine’s vulnerable, quill-less belly, and successfully attacked and ate it. 

Often, at this time of year, porcupines stake out their den trees (if they’re not inhabiting rocky ledges) by eating patches of inner bark, or cambium, with the exposed fresh inner wood announcing their occupancy.  Typically, if a tree den is used year after year, they gnaw off a portion of bark each year, sometimes eating the old, scarred portion which, due to previous chewing, lacks cambium cells, indicating that this behavior is not for the purpose of obtaining nutrients. ( photo: porcupine chewing near hollow tree den entrance)

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Your guesses were outstanding – especially “Pinocchio scat” and “petrified baby hippopotamus”– and a couple of readers even nailed it: part of the intestines of a porcupine. ( Many of you suggested it might be a black bear’s fecal plug – not a bad guess – though any bear that had to pass something this large when it woke up might decide to hibernate year round.) 

Mystery Photo Explanation: A fisher killed and ate a porcupine, choosing not to eat (and leaving behind) a portion of the porcupine’s digestive tract called a cecum – a sac located between the large and small intestine where the cellulose in leaves and bark that a porcupine eats are broken down. 

During the warmer seasons of the year, porcupines feed on sugar maple buds, leaves of basswood, aspen and beech saplings, grasses and other herbaceous plants, apples, acorns and beech nuts.  In winter, their diet consists mostly of leaves (mainly eastern hemlock in the Northeast), which contain low levels of nutrients and high levels of dietary fiber.  Certain mammals and birds possess specific bacteria that secrete enzymes capable of digesting the cellulose in fiber (beavers, hares, rabbits and ruffed grouse come to mind) through the process of fermentation.  Because these enzymes work slowly, the digestive tract of a porcupine is very long (26% of a porcupine’s total weight) and the fiber passes through it slowly. 

A majority of the bacterial activity in a porcupine’s digestive system takes place in the cecum, which is about the same size as a porcupine’s stomach.  Here fermentation turns finely ground woody material into molecules small enough to be absorbed by the porcupine’s body. ( A process referred to as “hind gut fermentation.”)  Research shows that 16% of a porcupine’s energy requirements are supplied by the porcupine’s cecal fermentation. 

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Porcupines spend a lot of their life climbing on and clinging to trees due to their woody diet.  In addition to strong, curved nails that fit into bark crevices, the soles of their feet have a pebbly surface with very little fur.  The bumpy texture increases the surface area and the friction when a porcupine’s feet are in contact with a branch, helping the porcupine hold onto the tree trunk and branches.  Even so, examination of porcupine skeletons confirms that many have fractures that have healed, indicating that a significant number of porcupines, while their bodies are adapted for climbing, still experience falls during their lifetime. ( Photos: porcupine footpad; insert – porcupine footpad in fisher scat)

During the summer, porcupines are almost always found out in the open.  At the end of October/beginning of November porcupines den up for the winter in the Northeast, with up to a dozen porcupines sharing the same den.  While some adult males will spend days at a time in a conifer, most porcupines seek out rocky crevices in which to spend the day, with a smaller number finding shelter in hollow trees.  Porcupines are hardy creatures – while dens do protect porcupines from heat loss, they contain no insulation, the entrances are open and the porcupines don’t huddle together for warmth.  In addition, porcupines emerge from their dens to feed at night, when outside temperatures are lowest. ( And yes, that is porcupine scat that is stuck in/on the porcupine’s quills.)