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Posts tagged “Erethizon dorsatum

Porcupine Quills

2-25-19 porcupine IMG_6292Porcupines 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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Porcupine Trails

1-12-18 mystery photo 049A2042Porcupines 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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Porcupine Preyed Upon By Coyotes

2-15-16 dead porcupine  086Coyote 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.

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Porcupines Marking Dens

3-25-15 porcupine den IMG_9681Often, 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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Porcupine Cecum

3-6-15 porcupine2 IMG_5163Your 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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Porcupine Feet Designed for Climbing

porcupine foot IMG_2659Porcupines 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)

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Porcupines Entering Winter Dens

porcupine IMG_2597During 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.)

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Opportunistic White-tailed Deer

white-tailed deer and nip twigs 008One of the most obvious signs associated with porcupines is the presence of “nip twigs” on the ground – severed tips of Eastern Hemlock branches dropped from above after porcupines have eaten the buds off of them. It usually doesn’t take long for White-tailed Deer in the area to detect this easily-accessible source of food. Tender tips that would be out of reach without the assistance of porcupines are quickly consumed by White-tailed Deer. Look for deer tracks and scat beneath trees in which porcupines are feeding. (Note wide porcupine path on left leading to den tree. All other trails were made by deer.)

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Porcupine Feeding Technique

12-18-13  porcupine incisor marks IMG_0150In the winter, the bulk of a porcupine’s diet is the inner bark, or cambium, of trees. The porcupine removes the outer bark (unless the tree is young or has thin outer bark and then it eats the outer bark as well) in order to reach the cambium layer, which lies directly beneath the outer bark. At this point the exposed surface is very smooth, more finely finished than the work of a beaver. Then the porcupine removes the cambium in small, triangular patches, each patch composed of five or six scrapes converging at one point, like sticks in a tepee. The point where the scrapes meet is where the upper incisors are placed and held fixed against the tree. The lower incisors scrape, making a fresh path with each scrape, as the lower jaw swivels in a narrow arc.

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Porcupines Giving Birth

4-18-13 porcupine IMG_9203It’s not easy being a female porcupine. You mate in the fall and are either pregnant (7 months) or lactating (4 months) for the next 11 months before you have one month’s break and begin this cycle all over again. This time of year porcupines are giving birth to one young that is covered in fur and quills and weighs about a pound. The young porcupette is born headfirst in a sac, in order to protect the mother from quill damage. Its quills are soft at birth, but harden within an hour. (Thanks to Kay and Peter Shumway for photo op.)


Porcupines Tapping Out

porcupine tap IMG_3494At least one porcupine got a jump on humans this sugaring season. A porcupine eats outer tree bark in order to access the phloem (layer of inner bark cells that transport nutrients) and cambium (produces phloem and xylem cells) layers of a tree, its primary winter diet. In eating these layers, the porcupine unintentionally cuts into the xylem, or sapwood, where water and dissolved minerals (sap) are transported between the roots and crown of the tree. Unintentionally, porcupines tap the trees whose phloem and cambium they eat. In this case, the weather had warmed up enough to cause pressure in the tree, which in turn caused the sugar maple’s sap to flow just as a hungry porcupine happened along. Soon thereafter, the temperature dropped, causing the sap to freeze, forming icicles. While they looked good enough to sample, one whiff of them told me that sap was not their sole ingredient! (They were located beneath the porcupine’s den in a hollow tree, from which urine flows freely.)


Porcupine Housekeeping

1-31-13 porcupine in ledge den IMG_2389A recent exploration of some rocky ledges, a favorite winter denning site of porcupines, revealed a virtual maze of trails leading to roughly a dozen crevices where porcupines sought shelter. A look inside these crevices confirmed that porcupines leave something to be desired when it comes to keeping house. Unlike many other animals that keep their dens pristine (e.g. beavers only defecate in water, never in their lodge), porcupines don’t feel the necessity to roust themselves when nature calls. As a result, the floor of their den consists of years of accumulated scat (and urine). In some cases, the pile of scat in these ledge dens was so high that it made you wonder how a porcupine could even fit into the crevice, and indeed, in some cases, porcupines do have to dig their way out of their den. When it became aware of my presence, the pictured porcupine assumed its characteristic defense posture, exposing its quill-filled back and upper tail surface to the intruder. It needn’t have worried, as the opening was barely wide enough to get the camera into, much less the photographer!


Porcupine Trail

porcupine trail IMG_0059It’s fairly obvious when there are active porcupines in the woods, as they leave all kinds of signs. The females, who often spend the day in a hollow tree or rock den, come out at night to eat (males often spend several days up in a tree), and leave very pronounced 6” – 9” trails back and forth to their feeding trees. Along this trail, in addition to an occasional quill, there are often pellets of scat as well as urine, which both your eyes and your nose can detect. Porcupines discard the tips of hemlock branches when they’re through eating the tender buds and leaves up in the canopy, and consequently the ground under a feeding tree is often littered with “nip twigs.”


Fisher Scat

Contrary to their name, fishers seldom eat fish.  While they prey on a wide range of animals and even plants, their preference is for small mammals (80% of their diet), snowshoe hares and porcupines.  Because fishers are well equipped to kill porcupines, and because there is little competition for them, porcupines are an important prey of fishers –up to 35% of fisher diet samples contain the remains of porcupines, as this photograph of fisher scat attests to.  There is no mistaking the bumpy porcupine foot pads (and quills)!


Porcupine Foot Pads

Given the amount of time porcupines spend in trees, it’s not surprising to see that their feet are well adapted for climbing.  Long, curved nails that grip the bark, as well as “pebbly” foot pads designed to prevent slipping allow this prickly rodent to climb just about anywhere it wants to.  (Hind foot pictured.)


Porcupines and Hollow Tree Dens

Porcupines leave plenty of signs where they have eaten the inner bark, or cambium layer, of a tree. Bark is missing on the trunk of the tree, leaving fresh, yellow wood exposed, which often bears incisor marks.  An observation I have made over the years is that porcupines often de-bark around or near their hollow tree dens.  Typically, if a tree den is used year after year, they gnaw off bark each year, sometimes eating the old, scarred portion which, due to previous chewing, lacks cambium cells. This has led me to wonder whether fresh de-barking in the vicinity of their tree den entrance might have more, or as much, to do with a  porcupine’s staking out a claim on that tree than with its sustenance.  I have never come across any research that even mentions this phenomenon, and would welcome feedback from anyone who has.



Porcupine Sign

Typically, male porcupines spend days at a time up in eastern hemlocks, eating the tender buds and leaves of branches, while females tend to spend the day in a den, and head for nearby food at night.  In the photograph, a porcupine den tree is on the left, with scat from the den having fallen on the snow below. The trail you see was made by the porcupine, as she went from her den tree to a nearby feeding tree.  Usually a den is chosen within a short distance of food, as was this one.  If you look closely at the uppermost quarter of the photograph, you will see a sign that indicates recent porcupine activity – nipped hemlock branches in the snow, that have been discarded by a porcupine, who’s feeding in the branches up above them.  It’s much safer to remain on a large limb and pull the desired tip of a branch in to you than it is to attempt to climb out on a thin branch.  Once the porcupine nips the tip of the branch off and eats the tender buds and leaves, it drops the branch to the ground below.


Porcupine Sign

Two inches of snow is enough for even the casual observer to be able to find signs of wildlife in the forest.  This hollow tree occasionally serves as a den for a female porcupine in which she rests during the day before heading out at night to feed on nearby hemlock leaves and buds. Porcupines make no effort to leave their den when they urinate or defecate, so eventually it builds up on the floor of the den and spills out onto the ground. You can see porcupine scat sprinkled over the snow (having fallen from the den entrance above) and if you look closely you’ll see several icicles near the lighter patch of wood on the tree trunk.  One whiff confirmed that they were none other than frozen porcupine urine.