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On the second Tuesday of every month at 7:45 a.m. and 5:45 p.m., we hear from our contributors in the field. Susan Knight and Gretchen Gerrish both work for the University of Wisconsin-Madison’s Center for Limnology at Trout Lake Station. Scott Bowe is the Director of Kemp Natural Resources Station.

Who Knew Porcupines Climb Trees?


I spent most of my life not knowing that porcupines could climb trees. While I am a little embarrassed to admit this fact, I am also not sure I spent a ton of time in my younger years thinking about it. Now that I know, I have become obsessed with staring toward the tops of trees trying to find a bound-up ball of quills, nested in the highest branches.

Early spring, before the trees fully leaf out, is an ideal time for spotting tree-dwelling porcupines who often move into the upper canopy of trees to eat and rest during the daytime. They commonly venture to the outermost or highest branch tips to break off newly budding twigs to eat. Trembling aspen and young hemlock bark are favorite foods for porcupines, but they will consume bark from a wide range of tree types and supplement their diet with fruits and ground dwelling plants and shrubs. While slow moving and lumbering on the ground, porcupines are adept climbers, alternately using their front and back claws to grasp the wood as they pull themselves upward.

More than 15 species of porcupines exist throughout the Americas and all are tree climbers. Most species have prehensile tails that can wrap around branches to assist in climbing and stabilization. Only one species, the North American porcupine, Erethizon dorsatum, can be found in the US and it does not have a prehensile tail. The North American porcupine is distributed throughout most of Canada and the northern forested regions of the US. Its range extends throughout the Rocky Mountains and all the way into western Texas and northern Mexico. Even though they can survive in warmer climates, porcupines are rarely found in central and southern US states.

The term porcupine is an Olde French term that translates as ‘thorny pig’ and applies to all the species of porcupines in the Americas and to 11 species of porcupines in southern Europe, Asia and Africa. Even though we call them all porcupines, the porcupines in the Americas are more closely related to guinea pigs and agouti than they are to the Eurasia/Africa porcupine species. Scientists who study the family tree of rodents, which includes rats, squirrels, guinea pigs, porcupines, beavers etc., clearly show that quills and the rounded porcupine body shape evolved two different times in separate ancestral rodent groups on different continents to give rise to the current distribution and diversity of ‘thorny pigs’ throughout the world.

While well known for their defensive quills, porcupines have numerous unique adaptations that allow them to succeed in our forests. When threatened, in addition to presenting their quills and whipping their tails, porcupines emit a strong odor that deters predators. Porcupines do not shoot out quills at predators, instead the quills stick into predators and are pulled out of the porcupine as the predator retreats. Small little hooks called barbs can be found on the ends of porcupine quills and these barbs act to imbed the quills deeper over time. Quills are hardened tubules of keratin, similar in composition to our own hair and fingernails. Like hair, the quills can fall out and new ones will grow back.

Some predators will brave such rigorous and painful defenses. Owls, coyotes, wolves, mountain lions, and bobcats are known to occasionally take down porcupines, but the most common predator is the fisher. Fishers are large weasel relatives that, like porcupines, are nimble tree climbers. They will attack porcupines in trees and get them to fall or descend to the ground where the fishers’ quick movements and slender body gives them the advantage. They circle the porcupine and continuously attack face to face, avoiding the quills until they can go in for the kill. This successful predation style makes fishers one of the only predators capable of controlling porcupine populations.

Heavy logging and intensive fur trapping in the 1920’s led to a substantial decline in the number of fishers in the Upper Pennisula of Michigan, and regions of northern Wisconsin around the 1920’s. With fisher almost extinct regionally, porcupine numbers soared and by the 1940’s porcupines were considered a pest in need of removal. For example, from 1954-1959, US Forest Service personnel eliminated 6,259 porcupines from the Ottawa forest. To control porcupine populations, fishers were reintroduced to areas during the late 1950’s and early 1960’s. Research supports that the regional reintroduction of fishers and reintroductions throughout the US and Canada have successfully reduced porcupine populations. The long-term work to rebalance fisher and porcupine numbers continues and this goal is set within the ever developing and changing forest landscape.

In the meantime, I will continue stumbling along forest trails staring upward instead of watching the ground, in pursuit of an illusive tree-climbing porcupine. If I get lucky this spring, maybe I can spot a mom and her tiny porcupette hiding in the branches.

Gretchen Gerrish works for UW-Madison's Trout Lake Station through the Center for Limnology. She studies how evolutionary and ecological processes interact to allow natural systems to deal with change over time.
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