So I started out yesterday not with the intention of posting about the new Frontenac Bird Studies MAPS program, but rather to write about this guy, who we startled as we were hiking through the bush. We were far enough off the trails, and the trails are infrequently hiked to begin with, that there’s a good chance that this particular individual almost never saw people, and was probably quite alarmed when we came over the hill. He scurried over to the nearest tree and quickly started hauling himself up the trunk.
It is, of course, a porcupine. More specifically, it’s a North American Porcupine, Erethizon dorsatum. There are 27 species of porcupines, found in both the “old” and “new” worlds. In the Americas, there are 16 species, most of which are found in South America. The only one to occur north of Mexico is this one, which is mainly a northern species. It also happens to be the largest of them all, growing up to 40 lbs (18 kg), an adaptation to the colder climate. Most are smaller, since they live in warmer regions – for example, the prehensile-tailed porcupines of South America are only about a foot long and weigh less than a kilogram (around 2 lbs).
Our “neighbour” at the north of the lake told us to be on the lookout for them, as this is “porcupine weekend”, so I wasn’t entirely surprised to find it. It was, in fact, the second one we’d seen – we’d already startled one shortly after we’d started out from the car. That one disappeared after cresting a hill, and must have either gone into a den or behind some rocks or something. Porcupines spend the winter in dens, often in the ground. They do not hibernate, but do spend a lot of the cold months sleeping. As they start to get more active in the spring, you start to see more evidence of them.
In particular, you’ll likely start noticing piles of their poop on the forest floor. The first time Dan and I found one we had no idea what it was. In the same way that you find little piles of rabbit or deer droppings, these were a pile of pellets, but pale brownish, the colour of sawdust, and shaped like macaroni. The sawdust colour isn’t all that surprising, as that is essentially the bulk of a porcupine’s diet. In the winter they mostly chew on the outer bark layer, denuding the trunks of trees but leaving the tree itself intact. However, they do also eat twigs and buds, particularly in the spring when there is tender new growth.
Those tender buds can get them into trouble. According to Wikipedia (which references a printed book called “The North American Porcupine”), porcupines occasionally fall out of trees in their attempts to get at these delectably tender new buds. This would be dangerous enough for the average animal, but is even more so for the porcs because they may fall on and stab themselves with their own quills. This is common enough, in fact, that porcupines have evolved to have an antibiotic coating on the quills which helps to prevent infection and speed healing.
This is also good news for Fido, should his curiosity get the better of him. The danger for Fido is more in quill tips breaking off under the skin, since these can potentially get infected. Like a fishing hook, the quills have microscopic backwards-pointing barbs that prevent the quill from easily being pulled out. However, if the tip does break off, it should eventually work its way out of the skin on its own, like a splinter might. A single porcupine might sport up to 30,000 quills, ranging in length from half an inch to four inches (1.2 to 10 cm), so it won’t miss a few dozen should it need to shed them in defense.
The quills are really just modified hairs, made of the same materials that form our fingernails. And like our hairs, they are controlled by tiny muscles in the skin attached to connective tissue around their bases. When these muscles are pulled tight, the quills stand on end, just like the hairs on your arm do when you’re cold. Porcupines have more control over these muscles than we do of ours, however.
Contrary to popular myth, porcupines can’t throw their quills, but they do release very easily. When the porcupine is relaxed and the quills flat, there is a fair bit of give in the connective tissue and muscles, but when tightened, the connective tissue tears easily. When a predator (or curious dog) applies pressure to the quill when it is standing upright, it pushes the quill backwards into the skin slightly, just enough to tear the connective tissue, which releases the quill from the skin. Studies have shown that it requires 40% less force to pull a quill out when the muscles are tight than when they are relaxed, a mechanism that helps prevent the porcupine from stabbing itself in climbing accidents.
Porcupines are rodents, and the North American Porcupine is the third largest rodent, behind capybaras and beavers. They have the same big rodent teeth that beavers do, and they put them to good use. Trees are their natural diet, of course, but of human wood products, they are partial to plywood, because of the salts added to it during the curing process. They’ll also target road salt used in the winter, both at the side of the road and where it accumulates on soft parts of vehicles.
And, of course, the answer to the question I know you’ve all been asking – how do porcupines mate? Well, let’s just say there’s not a lot of cuddling going on. The female, when she is receptive to a suitor, will curl her broad tail over her back. The underside is barbless, and if the male porcupine, who stands on his hind legs during the act, touches anything of the female it’s only the underside of her tail. On a related note, baby porcupines do have quills when born, but they’re soft, like your fingernails when you climb out of the shower. Within a few hours they have hardened enough to be effective protection.