Prying Into the Life of a Prickly Beast
They're surprising scientists with their intelligence and ability to "talk" to each other, so why do porcupines keep falling out of trees?
- Richard and Joyce Wolkomir
- Dec 01, 1993
There's nothing worse than worrying you might cause a porcupine to fall out of a tree," says researcher Molly Hale matter-of-factly as she positions a rock atop a picnic cooler to keep a drugged porcupine inside.
It's no idle worry. In a two-year study of porcupine ecology in a western Massachusetts forest, Hale and fellow University of Massachusetts researcher Sara Griesemer have seen ample evidence that, for a species that makes its living climbing trees, porcupines are, well, arboreally challenged. "The first porky we studied fell from a tree, cracked its skull and died," recalls Hale.
The large, prickly rodents have ample opportunity for missteps. They sometimes spend several days in the crotch of a tasty tree, and they don't hesitate to amble out to the skinny tips of branches to nibble the tender buds and leaves. Although evolution equipped porcupines for their treetop life with tail bristles that provide stability, claws to grip the bark and paws with nonslip nubbles, these attributes clearly aren't enough. Hale and Griesemer recall one porcupine they recently found dead with a leaf in its mouth, evidence it had tumbled during its last supper. Not all falls are fatal, though. "I saw one fall 30 feet out of a tree," recalls Griesemer. "He shook his feet and walked away." Hale and Griesemer have found many porcupines with injured legs and other problems that suggest falls.
Clumsy porkies are just one of the discoveries Hale and Griesemer have made as they study how porcupines find food and shelter in the forest around the vast Quabbin Reservoir. Working under the guidance. of University of Massachusetts biologist Todd Fuller, Griesemer concentrates on habitat-what porcupines eat, where they den, the trees on which the animals feed. Hale focuses on population dynamics, keeping track of mortality and survival rates, to deter-mine what factors-from human activity to the distribution of tree species-influence porcupine numbers.
Such ecological studies of porcupines have been few and far between. For the most part, biologists have worked out the physiology of captive porcupines, and have studied how the creatures damage timber and gnaw almost anything touched by perspiration to satisfy a craving for salt: Porkies have even been known to lick road salt off tires.
Scientists also know that porcupines spend most winter days in dens, venturing out of their rock piles and tree hollows only after nightfall to eat. In spring and summer, the 15-pound rodents have a taste for ground vegetation and the leaves of hardwoods, but in winter their appetites turn to bark, which has given them a reputation as tree killers.
Most of the ecological data date to the early 1960s, when University of Massachusetts biologist Wendell Dodge found that porcupines, contrary to their bad press, are not a costly tree pest in the eastern United States, since they keep to hilly, rock-strewn places that can't be logged anyway. Dodge also helped piece together porcupines' lackadaisical reproduction: Females, sexually mature at three years, bear a litter of one, once a year, for the duration of their 15-year lifespan. Dodge attributes the low fecundity to low mortality: A creature filled with quills has few enemies and need not reproduce like a rabbit to maintain its population size.
On this summer day, the two researchers tramp through the forest, Hale waving a radio antenna and Griesemer peering at the treetops. Their mission: tracking radio-collared porcupines. To slip on the collar, they must first trap their quarry. Griesemer and Hale set out scores of cage-type live traps, baited with Red Delicious apples. The day before, they had set a trap under a red oak and camouflaged it under fallen leaves. Two porcupines had been feeding high in the oak, one with a radio collar due for a battery change. But it climbed down at night and ignored the trap. Porcupines are smarter than they look, the researchers decided: "Once you've trapped a porcupine, you can never get it into a trap again," Hale sighs.
This morning, the other porcupine remains sprawled on a branch 50 feet up. Griesemer tries talking to it.
"Mmmmmmmmmmhh," she says.
The porcupine peers down.
"They make that `mmmmmmhh' sound during courtship," she explains. "Sometimes when I mimic them, we'll have a conversation. But I'm not sure what we're talking about."
If this porcupine comes down from the tree, Hale will grab it by the tail. "You have to be assertive!" she says, showing how she grabs one by the tail and yanks it into the air. And you have to avoid the quills. "They flail!" says Hale. When catching porcupines, the researchers wear thick gloves. "You do get quilled through the gloves sometimes, but it's not so bad," Hale says stoically.
Porcupine grabbing must be done before the animal has climbed too high. "It can swing down and hit you in the face," says Hale.
Next, says Hale, "I gently push a needle into its rump." Finding the right spot is hard because there are 30,000 quills (some as long as 4 inches) that obscure their features. The researchers lay the sleeping animal on a tarp and fit it with a radio collar and ear tags. They weigh it, take its temperature and draw blood for genetic studies.
While the porcupine sobers up, they put it in a plastic picnic cooler, which does not snag the quills. A rock on top keeps the animal from climbing out and waddling groggily toward trees. Since porcupines are less than adept at staying aloft even while cold sober (in one study of porcupine skeletons in museums, 35 percent had healed fractures consistent with falling), a drugged one hasn't a prayer.
At least the animals have evolved protection against one hazard of falling: self impalement. Biologist Uldis Roze of Queens College, studying porcupines in the Catskill Mountains in 1983, made that discovery when he got quilled in the upper arm as he tried to capture a 17-pound male in a beech tree. In three days the inch-long quill worked its way down his arm and out his forearm. Yet it caused no infection. Chemical analysis revealed that grease coating the quills contains antibiotics, which may have evolved to protect porcupines against their own quills.
Hale and Griesemer continue through the woods, eyes on selected treetops. Summers, the porcupines prefer basswoods. In autumn, red oaks are favorites. In winter, the creatures switch to hemlocks, with occasional snacks of white pine. Knowing the porcupine's seasonal tree preferences helps the researchers spot them. Another clue is fallen acorns: squirrels split open acorns and other creatures bore tiny holes, but porcupines leave the cap attached to the twig, the rest of the acorn eaten away.
The two researchers decide to check dens. They climb a slope jumbled with boulders, where they have marked dens. None is occupied, reinforcing their finding that the Quabbin porcupines do not enter their dens until November. Porcupines are not particularly social, but when dens are scarce they share. Grudgingly.
"We once found two porkies in one den and they were talking the whole time," says Griesemer. "I think they were arguing over whose log it was."
Usually, two porcupines together are either a mating pair or a mother and "porcupette." The young are born in May. Their quills quickly harden, ready for action. "The babies are incredibly cute, but they back up to you and they do swat those tiny tails back and forth," says Griesemer.
As Hale and Griesemer walk, they pick up "niptwigs," tree branches broken off by porcupines and dropped to the ground after they've nibbled on the leaves. The dropped twigs may augment the diets of ground dwellers. Porcupines also drop apples that mice and chipmunks then eat. And the porcupines partially defoliate trees, letting in more sunlight. As the study proceeds, the researchers expect to accumulate data on how porcupine activities affect the life of the forest.
Now the radio antenna leads them to another of their research subjects. Number 146 is in a white oak, sprawled on a high limb with all four legs dangling. "She's looking at us with her little beady eyes," says Hale.
Number 146 gazes down, looking serene. "I studied philosophy when I was an undergraduate," Griesemer says. "I like porcupines because they always look like they're thinking."