Winter Porkies

Deep winter and at last a good tracking snow had fallen. While I may puzzle over some tracks, there is no mistaking those of porcupines. They plow through the snow on their naked, flat, pigeon-toed feet like miniature bulldozers, and when the tracks freeze, deer, opossums and foxes use them as winter highways.

When we first moved to our central Pennsylvania mountaintop in 1971, seeing a porcupine was a rare occurrence, but over the last couple decades porcupine numbers on our square mile of property have proliferated. During several days in early January last winter I found abundant tracks and numerous porcupines along the trails and in a variety of trees. Tracks wandered into and out of our three-acre deer exclosure, in and around our Norway spruce grove, and along the Far Field Road. Porcupines sat high in trees beside our hollow road, on top of Sapsucker Ridge, down in Roseberry Hollow and near the top of a Norway spruce tree. The latter was snoozing as its quills whitened in the falling snow.

Without leaves on the trees I could see many debarked crown branches. On Dogwood Knoll I found tiny pieces of bark at the base of a large chestnut oak tree, a sign that a porcupine had been eating the inner bark of one of the favorite trees of some of our porcupines. They also like red oak and sugar maple. Because they prefer small branches near the tops of these trees, we rarely lose a hardwood tree to their winter gnawing.

But our Norway spruce grove is porcupine central in the winter. Like white spruce further north, Norway spruce is a favorite winter food for porcupines. In addition, it provides excellent protection from winter weather. Porcupines like hemlocks too, especially for protection, and they eat the needles and twigs but not the bark because it is too strong in tannins. Our hollow hemlocks used to be popular with porcupines in the deep winter, but as the hemlocks have thinned and, in some cases, died from the ravages of the hemlock wooly adelgids, porcupines, ever adaptable, have switched to other trees, most notably our Norway spruces.

Porcupine tracks led into the grove from Sapsucker Ridge and the Far Field Road. By late January numerous spruce trees bore fresh tooth marks from gnawing porcupines. Porcupines move slowly in the woods, just as I do, so they are easy for me to track. Unlike colder, northern places, where they are out mostly at night, here they are out and about both night and day. No doubt our porcupines were especially hungry last winter because the acorns, one of their favorite autumn foods, had failed for three years.

One day I surprised a porcupine sitting on the snow-covered Far Field Road. When I approached it, it stood up and slowly climbed a large sugar maple tree. Fifteen days later, in early February, I followed what may have been the same porcupine from the base of the spruce grove to the Far Field Road. The trail ended at the entrance to a hollow, fallen log below the road where a porcupine turned its back to me.

According to Uldis Roze, who has spent 24 years studying porcupines in the Catskill Mountains of New York state, porcupine fur has excellent insulating properties, which allows them to use hollow logs, trees, and rock crevices as winter dens. Usually they turn their backs to the den openings, sit with their bodies propped up by their tails, and hold their front paws against their chests. They turn their hind paws sideways so their naked foot pads don’t touch the ground. When resting in high trees, they roll up into balls and can withstand extremely cold temperatures. No wonder they are able to live as far north as northern Alaska, Quebec, and Labrador, in fact, at or beyond the tundra line.

By mid-February, the so-called “polar vortex” was not only dropping our thermometer to as low as ten degrees below zero on some days, but it began to snow in earnest. And again I found the same porcupine tucked into the hollow log along the Far Field Road, its back white with snow.

With 18 inches of snow on the ground, I broke out my snowshoes and headed up to the spruce grove. As I broke trail around the grove, I saw fresh porcupine tracks and then spotted a porcupine at the base of a spruce tree. It started up the tree when it realized I had seen it, but it didn’t climb more than a few feet before it went around to the back of the trunk as if once out of sight, I would forget it was there. Then I noticed a circle from its body at the base of the tree as well as a pile of cylindrical, gray and/or brown, inch to an inch-and-a-half-long porcupine scat (droppings). It must have been there for some time.

I also broke trail along the Far Field Road and encountered the porcupine in the same hollow log after a night of stripping bark from the lower spruce grove trees, just as the one I saw earlier specialized in the upper part of the grove.

Every time I passed the Far Field Road hollow log for most of February, the porcupine was either in the log or plodding its way back to it. And then tragedy struck. On February 27 I found a dead porcupine behind the spruce grove, still clinging to the thin branch of a black locust tree. Apparently, it had fallen from the large spruce it was gnawing and had broken the locust branch off on its way to the ground. Probably it had died sometime after it had hit the icy snow since there were puddles of urine around it.

Roze says, in his book The North American Porcupine, that porcupines risk injury and death from falling out of trees because they are relatively heavy and prefer to feed far out on branches that are often brittle. I know I’ve watched them foraging on hardwood tree branches, expecting them to fall any moment as they crawl farther and farther out on a limb that bends with their weight. Sometimes porcupines do fall, but they are usually badly hurt. For instance, one of Roze’s study animals had a series of injuries that he called “consistent with falling belly-first out of a tree.”

According to Roze, another researcher, Wendell Dodge in western Massachusetts, who autopsied 200 porcupines back in 1961, found healed leg, hip, and rib fractures, broken teeth, injured eyes and ears, hernias, and soft-tissue injuries. One even had a four-inch-long pine branch in its abdomen.

A week later, in early March, I checked on the dead porcupine and found a live one sitting next to it on the ground under the large spruce tree almost as if it was holding a late wake for it. Eventually it shuffled over to the spruce trunk, deftly climbed its mostly bark-stripped trunk, and moved far out on the limb.

I followed other porcupine tracks from the upper section of the grove over to the neighbor’s clearcut on Sapsucker Ridge. There I saw a small but old chestnut oak and a bent, larger one, both of which had debarked branches. Beneath them were bark pieces and scat littering the ground. I continued following the tracks for 20 feet to the remains of a hollow tree log left by the loggers. At its entrance was a huge pile of porcupine scat. I knelt down on the snow and peered inside the log. A porcupine was tucked into it.

Both log dens were 200 feet or so from the spruce grove. While porcupines wander much greater distances during the summer, their temporary winter dens, which they use for an average of 23 days, are usually within 300 feet of their food trees. The spruce grove porcupines followed that pattern.

The same porcupine appeared three days later at the base of the large spruce where the other porcupine had died and reluctantly climbed the tree when I spoke to it. It looked as if that beautiful tree had been completely girdled high up. So too had at least four other large spruces. But according to Gary Gillmore, a state forester, Norway spruces throw out new limbs if they have been topped.

By March 10 I was seeing as many as four porcupines feeding in our hollow hemlock trees, leaving nipped twigs and scat on our road. Although this was still winter food, probably they had left dens upslope early and were using hemlock habitat for shelter, meager though it was.

Near the end of March, I found only two porcupines in hardwood trees and they were eating buds. The rest seemed to have disappeared once spring arrived. But I had enjoyed my porcupine winter and the chance to learn a little about how they survive the cold months.

All photos taken on the mountain by Dave Bonta, except where indicated.