Think of the North American porcupine (Erethizon dorsatum) as a really fat, irritable, slow-moving squirrel. (The irritable part isn’t absolutely certain, but that’s the gist of the genus name, Erithizon.) Like squirrels, porcupines are rodents at home in the trees, with an affinity also for subterranean excavations. But while tree squirrels have evolved to eat and hoard nuts, porcupines are attuned to the leaves, twigs, and bark of trees. On our mountain, they seem fondest of conifers (hemlock, white pine, and Norway spruce), chestnut oaks, elms, and fruit trees, roughly in that order, but we’ve seen them in other trees as well. In warmer months, they may graze on herbaceous plants — there’s little that’s consistent about porcupines. Though generally nocturnal, you can find them out in the middle of a sunny day, too. I suspect they don’t always sleep too well. I hear them moving around under the floor at all hours.
For creatures that spend so much of their time in trees, porcupines have remarkably poor vision, relying instead primarily on their sense of smell and hearing. They certainly don’t look like they belong in the trees, especially when they climb out on a thin branch that bends under their weight. Watching this one today made me think of a trained bear on a unicycle — it just didn’t look natural. But their claws and the rough soles of their feet, together with their tails, seem more than adequate to any arboreal challenge.
I’ve often half-jokingly referred to them as my totem animal, but I don’t think I’m quite as strange as a porcupine — at least, not yet. Porcupines are legendary for their taste for salt, and have been known to eat tool handles, boots, snowshoes, or automobile tires encrusted with road salt. They also sometimes take a shine to radiator hoses and brake linings, and the glues in plywood are like porcupine crack.
Porcupines are fond of the dark insides of things, be they hollow trees, logs, or rock shelters, and will on occasion share sufficiently large shelters with other porcupines, each keeping a studious distance from the others. Though they’re quiet much of the time, they can make a lot of different noises when irritated or aroused. Mating season — late summer and early fall — brings out their full repertoire of coughs, grunts, whines, wails, and moans. Love-struck male porcupines are also said to perform elaborate dances, culminating in a spray of urine over the head of the female.
That may sound a little bizarre, but let’s face it: we’re talking about creatures who are fiercely solitary for most of their existence, and who spend way more time communing with the wind in the treetops than with others of their own kind. Oh, and there’s the matter of the 30,000 hollow barbed quills covering their bodies. That should be enough to make almost anyone a little strange, one would think.
Believe it or not, though, a coat of easily removable quills is a practical enough defensive strategy to have evolved twice. New World and Old World porcupines, like New World and Old World vultures, are not closely related, and resemble each other because of convergent evolution. It would be nice to say that similar ecological niches summoned them into existence — which was the case with vultures — but in fact it is only the New World porcupines that have a close affinity with trees. Many South American species actually have prehensile tails.
Porcupines have two main enemies here in Pennsylvania: people, and the large weasels known as fishers, which are quick enough to dart in, flip them over, and attack their unprotected bellies before they can react. We’ve found a number of dead porcupines around the mountain since the return of the formerly extirpated, reintroduced fishers some five years ago, though it’s possible that bobcats have also killed a few. Fishers are just as solitary as porcupines, and have huge territories, so the death of a fisher two weeks ago on a small road a half-mile from the base of the mountain was probably very good news for our porcupine population — and bad news for the trees that, for whatever reason, have the misfortune of attracting porcupines year after year.
The poor eastern hemlock (Tsuga canadensis) in the above video is one such tree. It’s one of the few hemlocks in the upper half of the hollow, and as such gets more than its fair share of attention from the conifer-loving porcupines. It’s undergone such radical pruning over the last couple of decades, I’m amazed it’s still alive, but hemlocks can take a long time to decide to cash in their chips. They’re not, however, the sort of tree to sprout a bunch of new branches in response to pruning, so this particular tree has simply become more and more skeletal, with vestigial tufts of needle-bearing twigs at the ends of most of its branches. Judging from the appetite of the porcupine I watched feasting on it today, this winter might well be its last. Porcupines can consume up to a pound of cellulose a day. This is said, by the way, to make them smell like old sawdust, though I admit I’ve never gotten quite close enough to one of them to see if that’s true.
Don’t forget to submit tree-related posts to the February 1 edition of the Festival of the Trees by January 30. Here’s the call for submissions. Ash laments that he has yet to receive any bark rubbings.