Laura Erickson's For the Birds

Porcupines

Last week I drove home from Iron River, Michigan, during a time when porcupines seemed to be on the move. Well, almost all of the ones I was encountering were no longer on the move—I found seven dead ones along the roadside, 5 on the Michigan side and 2 in Wisconsin. And the night before, when I was riding in a car with a careful driver, we slowed down as we approached a live porcupine. It turned its back on us, ready to swat us with its tail. And we did what it expected or hoped we would—went around it. These splendid rodents are born with an instinct to trust their quills no matter what. The barbs on the quill tips ensure that they’ll be difficult to get out, providing a very effective learning tool for predators who think catching one of these large, slow-moving and tasty rodents might be easy. But these quills are utterly worthless against people driving carelessly or too fast.

Some of the mammals that we think of as vegetarians do take some animal protein, too. White-tailed Deer, for instance, eat eggs and nestlings of ground-nesting birds. Porcupines may occasionally step on or dislodge a nest as they work their way to the outer branches of a tree, but as far as their diet goes, porcupines really are strict vegans—in spring they feed on leaves, twigs, and green plants such as skunk cabbage, lupines, and clover; in winter, they chew through the rough outer bark of various trees, including pines, fir, cedar, and hemlock, to get at the cambium. Like Ruffed Grouse, porcupines have bacteria in their digestive tract containing enzymes that help digest cellulose.

Porcupines tend to visit the same trees over and over again—you can recognize them by their cropped and stunted upper branches and bare wood. And beneath porcupine feeding trees you may find a litter of “niptwigs,” terminal branches of trees that have been cut off and their leaves or buds eaten. Although they tend to favor freshly growing wood in spring and early summer, when I was in Port Wing, Wisconsin several years ago, I followed some very loud scraping noises to an abandoned outhouse where a porcupine was chewing away.

Because porcupines don’t eat birds or food items that birds eat, except for the aspen buds they share with Ruffed Grouse, and don’t have a lot of interactions with birds, we don’t usually think of porcupines when we think of birds. But their arboreal habits give porcupines a view of the world quite similar to perching birds, and when they’re waddling from one tree to another, they have pretty much the same view as ducks, and even as thrushes. And like birds, porcupines spend the summer raising babies and gaining weight.

As the self-proclaimed Dr. Ruth of Ornithology, I’m often asked about bird mating behaviors, and some people also ask me how porcupines mate. There’s of course the easy answer—very carefully. In reality, mating is pretty much the same as it is in other mammals. When the female is sufficiently aroused, she relaxes her quills before raising her tail over her back. Mating takes place in fall, and the single baby is born in May or June, after the exceptionally long gestation period of nearly seven months. Babies are born with well formed quills, but fortunately for the mother, they’re born headfirst and the short quills are soft until after birth, when they harden within half an hour. The little baby grows and grows, quickly learning the lessons it must learn to spend its life in the treetops with the birds, or waddling on the ground from tree to tree, a gentle spirit that has few enemies except automobile drivers.