Every rodent has its thorns

Posted: Wednesday, June 17, 2009

Just the other day while bushwhacking through blueberries and wind-thrown trees, I startled a baby porcupine. It was really small; head and body together maybe reached seven inches, and it was very dark, without the yellowish guard hairs that adults have. Young and small, yes, but it had all the normal defensive reactions of turning its back and flaring its quills. In fact, little porcupines are able to do this almost immediately after they're born, even before their thousands of quills are fully hardened.

We don't seem to have a special name for baby porcupines - cats have kittens, dogs have pups, bears have cubs, and so on - but one well-known wildlife biologist has suggested we call them 'porcupettes'. I'm not sure that this label will stick, however...

Female porcupines have only one offspring a year. The young ones weigh one to two pounds at birth and can walk and climb right away. They drink their mother's milk for a few months but starting to eating green vegetation when only a few weeks old. Little porcupines stay with mom for four or five months, but by fall they are on their own.

Females mature at age one, but males take longer (about two years). Mating occurs in fall and the gestation period is about seven months - quite long for an animal of this size, usually weighing 15 to 20 pounds. Females are receptive for less than one day and usually mate only once each fall. After copulation, a plug prevents further mating for a while.

Most of the porcupines I see are rather quiet creatures, but the literature says quiet is not the rule during courtship. Males cruise around looking for receptive females and may fight and screech at each other if two of them covet the same mate. A courting male 'sings' to a female; the song is variously described as high-pitched, low-pitched, or like a meow. An unwilling female squalls and moves away, but a willing female lets the male approach and perhaps rub noses; they may wrestle and box for a while. The male gives her a shower or two of urine. Copulation is very quick and takes place in the common mammalian way, with the male behind the female. She curves her tail over her back, covering her quills.

Porcupines are the second largest rodent in North America after beavers. Their closest relatives are all in South America. Our porcupine arrived on this continent after the Central American land bridge between North and South Americas was formed about 3.5 million years ago.

When I walk through the woods around here, I often see hemlock trees with bark nibbled off at the base of the trunk. In contrast, spruce trees seem to be most vulnerable in the upper parts. Out my front window I can see a sorry-looking spruce, whose raddled top has no small upper branches except the erect leader, and no needles on the next lower tiers of branches. A porcupine spent several hours in this tree feasting. Some people fuss because porcupines can damage trees, but porcupines do less damage to forest trees than people do.

I recently watched a porcupine share a cottonwood tree with a black bear near the visitor center at the glacier. The bear occupied the tree top, pulling in branches to eat the male catkins. About fifteen feet below the bear was a phlegmatic porcupine, calmly doing the same. By the time the bear descended, the porcupine was out on a long limb, still eating and unfazed by the passing bear.

The most effective predator of porcupines is reported to be the fisher, which repeatedly bites the nose and face until the victim is so debilitated that the fisher can flip it over and get at the unprotected belly. Bobcats, wolverines, and large owls also capture some. However, another major cause of death is said to be falling out of trees. Despite their arboreal habits, porcupines are clumsy climbers. I suspect, but cannot prove, that some of them starve to death in winter.

• Mary F. Willson is a retired professor of ecology.



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