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Porcupines

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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Porcupine Tracks

2-5-16 w's porcupine IMG_3938Alas, yesterday’s Mystery Photo ‘twas not made by a squirrel loaded down with a bag of nuts, a guess hazarded by one reader, but, as most of you knew, it was created by a Porcupine, or Quill Pig (Erethizon dorsatum). A bit pigeon-toed, Porcupines walk with their feet pointed slightly inward, with their feet flat on the ground. Their pebbly soles rarely leave a distinctive pattern, and their toe pads are not usually evident, but under the right conditions, their nails do make an impression. Usually a Porcupine’s quill-laden tail is raised slightly as it moves, but occasionally it drags along the surface of the snow as the Porcupine walks, producing a broad band composed of very fine lines that weaves between the Porcupine’s tracks, as in yesterday’s photo.

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Porcupines Staying Warm Inside & Outside of Dens

If you’ve ever set eyes on a porcupine den, be it in a hollow tree or rocky ledge, you know that protection from the elements, especially cold temperatures, appears limited. While there is slightly better thermal protection in a rock den as opposed to a hollow tree, neither has any insulation, other than the ever-accumulating bed of scat on the floor of the den, and the entrance is wide open. Even so, porcupines save an average of 16% of their metabolic energy by occupying their dens instead of open terrain, due primarily to the shelter from wind that it provides. In addition, porcupines have two layers of fur which insulate them so efficiently that the outside of their bodies are approximately the same temperature as their surroundings, minimizing heat loss.

Porcupines do venture out of their dens and spend between seven and twelve hours a day outside, without the protection of wooden or rock walls. How can they survive this environment? When outside the den (usually when feeding at night), they are often in conifer stands, and a coniferous habitat provides the same energy savings as a den. Eastern hemlock, which is a preferred winter food, has needles layered so thickly that porcupines don’t lose a great deal of heat to the open sky. The trunks and foliage of hemlocks also re-radiate at night some of the energy they absorb in the day.

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Porcupine Artistry

1-5-16 porcupine incisor marks  634The patterns that a porcupine’s incisors leave when a porcupine has been removing bark down to the cambium can be a work of art. The way in which a porcupine makes these patterns is as intriguing as the patterns themselves. “The porcupine removes the bark in small triangular patches, each patch composed of five or six scrapes converging on an apex, like sticks in a teepee. The apex represents the position of the upper incisors, held fixed against the bark. The lower incisors scrape, moving over a fresh path as the lower jaw swivels in a narrow arc.” (Uldus Rose, The North American Porcupine) Fortunately, porcupine incisors, like those of all rodents, grow continually. Even though each incisor loses 100% of its length to wear in a year’s chewing, its length always remains the same. Juvenile porcupines leave a much less “organized” set of incisor marks (overlapping, randomly placed) than adults.

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Bountiful Apple Crop A Double-edged Sword When It Comes To Porcupines

11-5-15 apples and porcupines 011The outstanding apple crop this year bodes well for the fecundity of the white-tailed deer, mouse, black bear, raccoon, wild turkey and porcupine populations this coming year. There are other more subtle ramifications of this year’s bountiful soft mast production, however, one of which is an increase in porcupine salt-seeking behavior.

Porcupines are avid consumers of apples. Typically, the supply of apples is depleted by the end of August, when porcupines move on to beechnuts and acorns. However, this year the apple crop was so plentiful that many apple trees still bear fruit and will provide sustenance for wildlife well into the winter. High in carbohydrates, apples help porcupines gain the extra weight necessary to help them survive through the winter months.

That said, apples have a relatively low pH and are acidic, some varieties more than others. Porcupines prefer the less acidic apples, but even these contain several hundred times more organic acid than other food, such as poplar or basswood leaves, that porcupines consume in the summer. High acid intake impairs sodium resorption in mammalian kidneys, causing porcupines to lose sodium in their urine. Consequently, as a result of a high proportion of apples in their diet, porcupines seek extra sodium. While they find salt in aquatic plants, insects, animal bones and outer bark, porcupines are also drawn to plywood, car tires, outhouses, sweat-soaked tool handles and other human-related sources of sodium. This would be a good year to make sure your hammers, hoes, rakes and shovels are well out of the reach of quill pigs. (Insert shows porcupine incisor grooves in flesh of apple. Porcupines often leave cores, avoiding eating the cyanide-rich apple seeds.)

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Porcupines Foraging

10-1-15  porcupine in leaves IMG_2537There are a few weeks in September and October when acorns (and beechnuts) are mature enough to eat, but haven’t yet fallen to the ground. Porcupines take advantage of this nutritious supply of food that is not yet accessible to small rodents, deer and turkeys, and climb oak trees to consume acorns. Because an average porcupine weighs between 12 and 35 pounds, it is unable to climb all the way out to the end of a branch, where acorns are located, so it nips off the tips of fruit-bearing branches and then scoops out the acorn, leaving the cap still attached to the branch (diagnostic porcupine sign). When all the acorns on a branch have been eaten, the branch is discarded. You can often find many of these branch tips, or “nip twigs,” in the canopy of large oaks on a good mast year, but inevitably some fall to the ground. The end of the twig is usually cut at a 45° angle, and often you can see the lines made by the porcupine’s incisors. (Beechnuts are also harvested in this manner, as are the cones and terminal buds of eastern hemlock in winter.) Red squirrels also nip twigs in order to reach fruit, but typically do so when they harvest the cones and terminal buds of conifers. (Thanks to Ethel & Michael Weinberger for photo opportunity)

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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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