Cooperative Extension ServiceCollege of Agriculture

B-1073May 1999

Table Of Contents

Introduction .................................................................................................................................... 1

Species Description .......................................................................................................................... 1

Distribution ..................................................................................................................................... 3

Habitat Characteristics ..................................................................................................................... 3

Den Types .................................................................................................................................. 3

Food Habits ..................................................................................................................................... 4

Spring ........................................................................................................................................ 4

Ground Feeding ................................................................................................................... 4

Salt Demand ........................................................................................................................ 4

Summer ..................................................................................................................................... 5

Fall ............................................................................................................................................ 5Winter ....................................................................................................................................... 5

General Biology ............................................................................................................................... 6

Defense Reaction ....................................................................................................................... 6

Reproduction ............................................................................................................................. 7

Social Structure .......................................................................................................................... 8

Life Span.................................................................................................................................... 9Winter Adaptations ................................................................................................................... 9

Digestive System ...................................................................................................................... 10

Damage Problems and Economic Impacts ..................................................................................... 10

Tree Damage ............................................................................................................................ 10

Damage from Salt Demand ..................................................................................................... 12

Legal Status .................................................................................................................................... 12

Damage Prevention and Management Techniques ......................................................................... 12

Non-Lethal Techniques ............................................................................................................ 12

Ecological Methods ............................................................................................................ 12

Exclusion ........................................................................................................................... 12

Repellants .......................................................................................................................... 13

Biological Options ............................................................................................................. 13

Live Trapping ..................................................................................................................... 13

Lethal Techniques .................................................................................................................... 14

Shooting ............................................................................................................................ 14

Poisoning ........................................................................................................................... 14

Trapping ............................................................................................................................ 14

Summary ....................................................................................................................................... 14

Acknowledgements ........................................................................................................................ 16

1

Introduction

The porcupine (Erethizon dorsatum) is acommon resident throughout Wyoming andthe western United States. It is found in a widerange of habitats, including coniferous forests,cottonwood stands along prairie river bottoms,deserts, and alpine tundra. The name “porcu-pine” comes from the Latin porcus, meaningswine, and the French epine, derived from theLatin spina, meaning thorn. It literally means“the irritable back.”

Species Description

Porcupines are large rodents of theErethizontidae family. Unlike other large NorthAmerican rodents, their bodies are modified forclimbing and maneuvering in trees and feedingon bark, fruit, and leaves. Most members of theErethizontidae family are tropical animals.However, Erethizon dorsatum has adapted tosurvive in extreme cold conditions, up to thetree line in far northern areas.

Best known for their pilage of quills, adultporcupines have approximately 30,000 largequills covering the dorsal and tail regions. Moreslender and elongated quills blanket theshoulders and sides of the body. Quills arehidden under long, white-tipped guard hairsuntil animals are agitated or in a warningposture. Guard hairs shed rain, sleet, and snowand convey tactile information from theimmediate environment. These hairs are black,brown, or chestnut in color, 6 to10 inches long,and give porcupines a fluffy appearance. Albinoporcupines have been observed but are exceed-ingly rare.

Porcupines have several adaptations for climb-ing trees to reach food. Both front and hindfeet have extremely long claws protruding fromthe toes that can be inserted into tree barkcrevices to aid in climbing. The four claws onthe front feet and five claws on the hind feet areused as a comb during self-grooming. They arelong enough to extend through the quill layer

to the skin. Front claws are used to manipulatefoods, such as fruits and small branches, and topull tree branches into feeding range.

Front and hind footpads resemble rubber witha pebble-like texture from structures calledtuberosities, which are used to increase frictionagainst the tree trunk. Footpads are used solelyfor climbing small tree trunks or branches thatare too narrow in diameter for claws. Footpadsize increases with body size, and males gener-ally have larger footpads than females.

The tail is used for climbing trees. Stiff,backward-pointing bristles on the tail under-side are pressed against tree bark while climb-ing. This provides an anchor against the barkand prevents downward sliding. By moving thetail up and down prior to each claw-hold andfeeling the path below, the tail is used as aquick guide stick for crawling down a tree. Asporcupines climb up and down trees, theirbellies and underarms continually rub againstthe trunk, resulting in an absence of quills inthese areas.

A tree-climbing adaptation of the porcupine isthe absence of an external male penis and theaddition of a membrane covering the femalevagina. In males, the penis is retracted into acloaca-like structure by muscles attached to atiny bone (the baculum) inside the penis. Infemales, a membrane covers the vaginal open-ing for protection against bark scrapings anddebris while climbing. These characteristicsmake it difficult to distinguish males fromfemales by casual observation.

Porcupines are the second largest member ofthe rodent family in North America, next tothe beaver. In the Catskill Mountains of NewYork, male porcupines averaged 13.4 poundswhile females averaged 11.2 pounds. In shrubdesert areas porcupines are generally larger,with one study reporting an average weight of25.3 pounds for adult males. Porcupines thatevolved with smaller deciduous trees andbranches are generally smaller in size due to

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difficulties associated with feeding among smallbranches. Weight varies by season since porcu-pines store a considerable amount of body fatat the beginning of winter and lose all stored fatby spring. The average length of a mature adultvaries from 25½ to 36½ inches. Weightvariation from young to mature adults variesfrom 7¾ to 39 pounds. Tail lengths, which arecritical for defense from predators, range from5¾ to 11¾ inches.

Distribution

Porcupines are found throughout Canada andthe western United States (Figure 1). InWyoming, their distribution covers all regionsof the state. Originally from South America,porcupines are an ecologically adaptablespecies, spreading as far north as Alaska. They

are found in deciduous forests, low deserts suchas the Mojave in California, high desert regionsof the Great Plains, and coniferous foreststhroughout the western states.

Porcupine presence is detected by identifyingpellets or scats beneath feeding or resting trees.Another distinguishing feature of porcupinepresence is discarded “niptwigs” on the groundunderneath a feeding tree. Niptwigs areterminal twigs stripped of leaf blades anddiscarded by feeding porcupines. Niptwigsoften are eaten by deer and other mammals.

Habitat Characteristics

Den TypesPorcupines use dens for temporary shelter fromrain, snow, and insects or for protection duringwinter. The two types of dens, pre-winter and

Figure 1. Distribution of the porcupine (Erethizon dorsatum) in North America (Dodge 1982).

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winter, are different in structure and location.Pre-winter dens are usually near favoriteroosting or feeding areas and consist primarilyof hollow trees. Winter dens are generally rockcrevices in steep-sloped areas and located awayfrom their preferred roosting or feeding sites. Astring of below freezing temperature daysstimulates porcupines to enter a permanentden. Where rock crevices are used for dens,porcupines commonly come out to feed atnight.

Although porcupines prefer rock crevices forwinter dens, if these are not available, caves,live hollow trees, hollow logs, human outbuild-ings, and thickly branched crowns of evergreensare suitable substitutes. Den use by porcupinesis not mandatory, and some animals remainoutside all year. This is especially true in areaswhere evergreens are abundant and no suitablerock crevices are available. Hemlock, Douglasfir, white spruce, yellow pine, and white fir arefavorite trees for winter survival. In addition toproviding shelter, these conifer trees alsoprovide a convenient food source.

Porcupines do not use bedding or nesting materialin the den but, instead, prefer a dry floor devoid ofleaves and debris. Large accumulations of fecesoccur since dens are used year after year. In moist,temperate climates, feces are decomposed by mites;however, in dry, arid climates, accumulated fecesform into an extremely hard concrete-like mass.

Two factors influence springtime exit from aden: a series of days where temperatures areabove freezing and decreased snow pack. Inareas of deep, fluffy snow where travel isdifficult, porcupines leave den sites only whensnow pack diminishes.

Porcupines are nocturnal animals and active allyear. However, much time is spent resting intrees called “rest trees.” Use of a den or rest treeis evident by the presence of broken quills,recent scats, and the pungent odor of urine.Rest trees are a critical component of theirhabitat, even during adverse winter weather

conditions. These trees may be deciduous orconifer species but a common characteristic is adense crown that provides cover and protectionfrom predators (Figure 2).

Food Habits

Spring

Ground Feeding

During spring and early summer, porcupinesgorge on a variety of ground vegetation, addingvaluable weight in preparation for the nextwinter (Figure 3). There is geographicalvariation in feeding behavior. In deciduousforests, porcupines do not need ground vegeta-tion to compliment their diet, although somehighly preferred foods, such as raspberry leaves,are consumed in excess when available. In highdesert shrub areas, porcupines forage almostexclusively during the night to avoid thedaytime heat.

Spring feeding on ground forage is controlledby snow cover. When there is no snow cover,porcupines feed exclusively on whatever groundvegetation is available and edible. Dietary itemsinclude grasses, flowers, dandelions, floweringherbs, and various other vegetation. Porcupinesin western Douglas fir-juniper forests feed onground vegetation in spring and return to a diet

Figure 2. A typical “rest tree” for porcupines consistsof a dense crown that provides cover and protectionfrom predators.

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of tree bark and evergreen needles after herba-ceous forage dries out. Southwest porcupineswill eat shrubs such as gooseberry, plums,chokecherry, buffaloberry, elder, black haw,raspberry canes, and buckbrush. Herbaceousplants in their diets include geranium, lupine,cinquefoil, wyethia, and lousewart. Porcupinesin Wyoming commonly eat agoseris flowerheads, American bistort, alpine bluebells, alpinebuttercup, mountain clover, and dwarf willows.

Porcupines gain weight rapidly in the spring,feeding on nitrogen-rich forage. High nitrogenintake and changing climate trigger winter furmolting. The molting process is completed in amatter of days, leaving only the guard hairs,quills, and tail bristles. This rich spring diet hasother consequences—a loss of sodium andsubsequent desire for salt.

Salt Demand

Porcupines find salt in salt-enriched soils,plants, road salt, wood, and various otheritems. These animals have been reported eatingmud in salty-soil areas and wading in ponds toconsume various plants, such as yellow waterlily and aquatic liverwort, which have high saltconcentrations. Rock salt, left over from saltingwinter roads to improve travel, is anothersource of sodium. Plywood, human-handledwood posts and timbers, fresh animal bones,old shoes and boots, paint, and the outer barkof trees contain sources of salt as well. Anyobject impregnated with urine also attractsporcupines because of the salt content.

SummerPorcupines alter their feeding behavior inresponse to seasonal plant species changes andfood resource availability. During summer,ground vegetation (skunk cabbage, clover,lupines) comprises up to 85 percent of theporcupine diet. The remaining 15 percent istree-gathered material, primarily bark. Theseherbaceous animals feed primarily on inner treebark, twigs, and leaves with a preference for

Ponderosa pine, aspen, willow, and cotton-woods. Porcupines prefer trees with a thin,smooth bark as opposed to a thicker bark.Hence, young trees with thin palatable barksare often targets for foraging porcupines.

FallDuring fall, porcupines substantially increasetheir intake of tree-gathered materials for forageto approximately 72 percent. Ground vegeta-tion becomes less prevalent due to decliningnutrient content and lower availability becauseof snow cover.

Porcupines in deciduous forests commonlyremain within a small home-range area year-long due to abundant food sources. However,in western mountainous regions, such asWyoming, porcupines have much larger home-range areas and wander extensively to fulfillnutritional requirements. Mountains, foothills,and desert or sagebrush areas provide variedforages at different times of the year. Porcu-pines foraging during the fall travel throughareas that provide adequate feeding opportuni-ties while enroute to their winter habitat. Theseare usually areas of rocky terrain interspersedwith adequate trees for foraging.

In desert or sagebrush habitat, porcupines maytravel toward foothills or riparian zones alongrivers where trees are abundant. Porcupines inhigh mountain meadows may travel fromalpine areas down into spruce-fir forests.

Porcupines use many tree species for food;however, differential abundance of thesevarious species influences their dietary choices.Porcupines prefer acorns, beechnuts, piñonnuts, chokecherries, mushrooms, corn, mistle-toe, and other types of fruits and nuts whenavailable. Their preference for mistletoe isconsidered beneficial to forest health.

WinterIn winter, porcupines feed exclusively on treematerials such as tree bark, twigs, buds, and

5

evergreen needles. Specific tree species used forwinter food vary between vegetative commu-nity types. One study in Minnesota docu-mented different food habits between twoporcupine populations only four miles apart(e.g., the first population used mainly whitepine, elm, and linden in its diet while the otherused these three tree species for only 23 percentof its diet. Red oak, quaking aspen, and whitepine were the primary species used by thesecond population). Generally, porcupines arenot finicky eaters, using whatever species aremost abundant in their area, provided they arepalatable. Major winter foods of North Ameri-can porcupines are listed in Table 1.

Porcupines cannot travel easily through snow.Therefore, winter activity and feeding can be asmuch as 90 percent less than spring andsummer activity. Winter home-range areas areconsiderably smaller than summer home-rangeareas. However, when snow is crusted over,porcupines can feed freely and travel withoutmuch difficulty. When topography and winterweather conditions favor porcupine movement,they may not display any difference betweensummer and winter foraging habits. Thedistribution of den sites, their proximity towinter forage, and the amount and type ofsnow pack determine the extent of porcupinemovement.

General Biology

Defense ReactionPrior to engaging in a fight, porcupines willwarn their attackers by displaying their quills,omitting threatening vocalizations, and produc-ing an offensive odor. Porcupines use theirquills as a last resort for defense.

Conspicuous black and white markings arevisible to most potential predators from a backview. This contrast is due to the whitequillshafts against the darker fur and is easilyseen in the dark. Although western porcupineshave light brown fur, the contrast is still evident

(Figure 4).

Young porcupines do not have this black andwhite coloration, but rather depend on con-cealment as a protection against predators. Asthey mature, the warning coloration of an adultdevelops. By three months old, porcupines havewell-defined warning coloration.

Teeth clattering also warns potential predators.Porcupines deliberately shiver their bodies andsimultaneously close their jaws, causing theincisors and cheek teeth to vibrate against oneanother. Teeth clattering may only last for 30seconds, but it can be repeated many times.Porcupines only do this if an encounter isimminent.

Another warning is smell. A powerful odor isemitted from an area of skin above the base ofthe tail called the “rosette.” Only short, dark-colored quills cover the rosette without fur orguard hairs.

If all three warnings are ignored, porcupinesuse their quills when attacked. Quills aremodified guard hairs, thicker than normalguard hairs and filled with a spongy matrix thatmakes them light and stiff. Quill tips have tinyfish-hook barbs that make removal difficult.

Figure 3. Porcupines depend on open coniferous forestareas with adequate understory ground vegetation forspring and summer foraging.

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Upper back and neck quills are the longest,about four inches, and lie flat toward the tailwhen unaroused. When provoked, these quillsstiffen up randomly in all directions, providinga defense against any approach to the porcu-pine. When a charging predator makes contact,quills are embedded barbed-end first by thepredator’s momentum.

The upper tail surface has short black quillsthat are much more dangerous than the longerback and neck quills. With a tail slap, thesequills become internal projectiles, embeddeddeeply into the skin of an attacking animal.There are documented cases where a quill hasperforated a man’s intestine and caused death.Infections seldom occur from embedded quills,however, since they have antibiotic properties.

ReproductionMating occurs in the fall (September toNovember) with a gestation period of approxi-mately seven months. Reproduction is con-ducted by the conventional method of most

mammals, while the female’s quills are relaxed.A single offspring is born in May or June. Thequills, developed at birth, are not injurious tothe mother because of protection from theplacental sac and the predominate moisturecontent of new quills. However, quills dry andharden within hours.

Newborn porcupines are fully developed atbirth, usually weighing about one pound. Theygrow rapidly, doubling their weight in abouttwo weeks. Although young porcupines canflick their tails within an hour after birth, theirbest defense is hiding. Young porcupines areessentially odorless, making it difficult forpredators to locate them. In addition, defeca-tion is stimulated by the mother during thisearly period, and the droppings are eaten toeliminate any fecal odor, which may attractpredators. When old enough to climb, youngporcupines spend more time in trees as evi-denced by the accumulation of tiny droppingsunder trees.

Porcupines normally give birth to only one

Table 1. Major winter foods of porcupines in North America (Roze 1989).

seicepSdooF noitacoL ytirohtuA

radecetihw,securpS

hceeb,kcolmeh,radecetihW

elpamragus,hceeb,kcolmeH

ecurpsder,kcolmeH

elpamragus,hceeB

enipkcaJ

elpamragus,kcolmeH

hcribwolley,elpamraguS

noñip,rifsalguoD,enipwolleY

ollitocO

enipasorednoP

eniprebmil,rifsalguoD

enipwolleY

securpS

kciwsnurBweN

eniaM

sttesuhcassaM

)skcadnoridA(kroYweN

)sllikstaC(kroYweN

oiratnO

nagihciM

nisnosiW

anozirA

tresedanozirA

ohadI

atreblA

nogerO

aksalA

8791,htrowliDdnareepS

4491,sitruC

7691,egdoD

9491,oripahS

4891,ezoR

2591,dlanoDcaM

3791,rednarB

2691,.lategnitferK

5391,rolyaT

7591,sdlonyeR

3591,nosliWdnasitruC

9791,redraH

8291,nosleirbaG

6291,eiruM

7

offspring each year. The female nurses theyoung from a pair of nipples located under thearmpits and another pair on the abdomen. Thefemale sits upright on her haunches and tail,allowing the newborn access to her quill-freeabdomen. Nursing lasts approximately 127days, following the 210-day gestation period.Therefore, females spend 337 days of the yeareither being pregnant or lactating. Porcupinesmust nurse their young for a long time becauseof the inherently poor nutritional quality of aleaf and bark diet.

Adult females do not wander far from theoffspring during the first six weeks after birth.Young porcupines can climb small sapling-sizetrees, but these smaller trees are often difficultfor adults to climb. Therefore, mother andinfant meet only at night on the ground.Generally, though, adult females sleep in aresting tree during the day, with the babyhidden on the ground in hollow bases of trees,rock crevices, under fallen tree trunks, and inslash piles.

As young porcupines mature, the separationdistance between mothers and their offspringincreases during the day due to greater traveldistances. At night, however, mothers alwaysreturn to the young from distances as far awayas a half mile. While accompanying theirmothers, young porcupines learn locations offood trees, dens, shelters, and hiding places.Weaning occurs at the end of the mating seasonin late fall. Male offspring may remain withinthe mother’s home range in the fall, but femalesgenerally leave. Young porcupines spend theirfirst winter alone and reach sexual maturityduring the third year after birth. Males com-monly mate with more than one female toensure species perpetuity. This is importantsince reproductive rates are low.

Social StructurePorcupines are solitary animals throughoutmost of the year, except during the fall breeding

season. During the breeding season, males areattracted to females by scent. At this time,males will fight with each other over femalesand territory. Encounters between males at saltsources have been described as “agonistic,”accompanied by high vocalization. In captivity,males will commonly kill each other.

Although there is not a lot of information onporcupine social behavior, there is evidence ofsome social interaction. Related males com-monly have overlapping ranges and developloosely tied associations with each other.Encounters between males acquainted witheach other are tolerated, but meetings betweenmales from different associations result infights.

Adult females are even more intolerant witheach other, mainly because they share limitedresources in a smaller home-range area com-pared to males. Even mother-daughter encoun-ters cause fights after the daughter matures.Unlike males who expand territorial areas asthey mature, females maintain small and highlydefensible territories. Home-range areas ofmales may overlap as many as five female home

Figure 4. Displaying their quills is one warning thatporcupines use to fend off potential predators. Con-spicuous black and white markings from a back vieware due to the contrasting white quills against theirdarker fur.

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ranges. Increased competition for breeding in asmaller female home-range induces adult malesto disperse and colonize other territories. Thissituation occurs approximately every four years.Also, yearly differences in food supply maycause porcupines of either sex to disperse at anytime.

Life SpanPorcupines have generally low mortality rates,with an average life span of seven to eight years.Common causes of mortality are disease, winterstress, injury, and human predation. Scabies,caused by the mite Sarcoptes scabiei, causes highmortality among porcupines; other parasitesinclude lice, ticks, tapeworms, and nematodes.In severe winters, porcupines die from pro-longed sub-zero temperatures and heavy snowpack, which limits access to food material. Insome cases, porcupines injure themselves fallingout of trees.

Porcupines have few natural predators, al-though fishers are probably the most efficientat killing porcupines. Fishers can overturn aporcupine easily, exposing the unquilled ventralside to a fatal attack. However, fishers are oftenfatally injured during this encounter. Othernatural predators include mountain lions,bobcats, horned owls, coyotes, fox, black bear,and marten.

Winter AdaptationsPorcupines have developed two primaryadaptations to survive extreme winter tempera-tures: a thick fur undercoat and changes inmetabolic rates to maintain body temperature.A thick, dense fur undercoat develops in thefall as temperatures start dropping. By earlywinter, this fur is so dense that all quills, exceptthe short rosette quills on the base of the tail,are hidden. During early summer, the fur iscompletely molted to start the cycle of furdevelopment again. Although they don’tprovide much warmth, the four other types of

hair are: quills, bristles (found on the tailundersurface), vibrissae (whiskers), and guardhairs.

Another mechanism used to survive extremewinter temperatures is adjusting metabolic rate.Normal basal metabolism, in conjunction witha dense fur undercoat, is adequate to maintainbody temperature in outside temperaturesdown to -4 degrees Celsius. However, asoutside temperatures drop below -4 degreesCelsius, porcupines increase their metabolicrates to compensate.

Digestive SystemPorcupines feeding on leaves and bark consumea high percentage of dietary fiber, most ofwhich is not easily digested by mammaliandigestive enzymes. Some examples of complexfiber molecules are celluloses, lignin, andpectin. However, bacteria that can digestcelluloses and hemicelluloses are found in theporcupine’s caecum, a large sack located at thejunction of the small and large intestines. Sincedigestion of dietary fiber takes a long time withthese bacteria, the large intestine is extremelylong, resulting in a slow passage time. Thispermits maximum absorption of the fermentedproducts of the caecum.

Cellulose digestion provides another benefit—additional protein metabolism. A by-product ofprotein metabolism is urea, which is normallyexcreted in the urine. However, the bacteria inthe caecum also break down urea, improvingwater absorption and reducing kidney func-tion. This function allows porcupines to extractmaximum water amounts from consumedfoods. This is especially significant for porcu-pines residing in desert areas or when porcu-pines remain in a feeding or resting tree forprolonged periods.

Foods consumed by porcupines must bereduced to dust-like consistency for efficientbreakdown by digestive bacteria. Porcupineshave 20 teeth to accomplish this task: 4

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incisors, 4 premolars, and 12 molars. Incisorteeth continually grow and require constantwear to maintain proper length. The premolarsand molars are collectively called the “cheekteeth,” and are located far back in the jawsbehind a large empty space called the “di-astema.” The lips are collapsed over the di-astema space while chewing, allowing porcu-pines to cut food materials with their incisorswhile keeping their inner mouths closed. Cheekteeth move in a front to back motion whilechewing—not sideways as in humans. Theseteeth have fixed growth roots and can be worndown to the gum line in older animals. Porcu-pines over 12 years old are typically lighter inweight due to restricted food consumption as aresult of worn cheek teeth.

Damage Problems andEconomic Impacts

Economic losses from porcupines feeding onforest plantations, ornamental trees, and fruitorchards and damage to human articles con-taining salts (i.e., leather products, wood-handled implements, and fence posts) can beconsiderable. Porcupines usually are toleratedexcept where high-value ornamental plantings,commercial timber, nursery stock, or orchardtrees are damaged by girdling, basal gnawing,or branch clipping. Often, tree diametergrowth is restricted or young saplings are killedfrom porcupine feeding.

Tree DamageMost porcupine feeding on mature trees occursin the crown where preference for leaves,terminal twigs, and young bark prevails (Figure5). This type of feeding activity does not killthe tree, but it causes lateral branching invarious directions where terminal branches areremoved. Successive years of pruning terminalbranches result in short growth form withseveral twisted, odd-shaped limbs. Trees that

develop an “eerie” growth form due to porcu-pine impact are commonly called “witch trees.”Trees most susceptible to mortality are youngsaplings where porcupine feeding on theground results in basal girdling.

Porcupine feeding activities can influence thestructure and plant species composition of theforest, especially near their winter dens. Sinceporcupines feed close to winter dens andoccupy the same dens each year, trees in theseareas sustain heavy impact year after year.Although in some situations, this impact mayresult in long-term ecological diversification offorest vegetation. In this scenario, trees pre-ferred for feeding are suppressed, allowingunpreferred tree species to compete for existingsoil and water resources. Eventually, this resultsin a more diverse plant community structure.In addition, feeding in the canopy of maturetrees reduces canopy cover, permits more lightpenetration to the forest floor, and stimulatesmore herbaceous understory plant production.A more diverse understory plant communitycan provide better habitat conditions forwildlife species such as ruffed grouse, snowshoehare, white-tailed deer, moose, morningwarbler, yellowthroat, and a variety of othersongbirds and small mammals.

Porcupines also provide another benefit toforest birds by providing shelter and nest sitesin hollow tree trunks. Porcupine feedingactivities may expose the tree’s heartwood areawhere sap and soft inner plant tissue attractinsects used by birds as a food source.

In 1957, Weyerhaeuser, Inc., completed a studyclaiming that a single porcupine could destroyapproximately $6,000 worth of timber duringits lifetime. Researchers claimed the majority ofdamage was due to girdling of Ponderosa pineseedlings, with lesser damage to lodgepole pine,white fir, Douglas fir, and spruce. Timbercompanies frequently cite porcupines forextensive damage to commercial plantations

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but rarely describe the location and size of thedamaged area, methods used to estimatedamage losses, and considerations of otherpotential forest animals as perpetrators of treedamage. Before blaming porcupines, otherpotential causes of damage (such as deer,rabbits, drought, fungi, insects, excessive soiltemperatures, and competition from invasiveplants) should be considered.

Other economic losses from porcupines includedamage to ornamental trees planted aroundsummer cabins, vacation homes, and ruralhomesteads. In some areas, damage to fruit andnut orchard plantations by porcupines can beextensive. There also have been reports ofporcupines damaging corn, small grains, andalfalfa fields.

Damage from Salt DemandAlthough porcupine damage to woodenstructures and human articles containing salt isgenerally minimal, there are situations wherethis type of economic loss can be high, espe-cially in areas of high porcupine density atcertain times of the year. Any item containingsalt can attract porcupines. Examples areleather goods, saddle blankets, old shoes, freshanimal bones, wood-handle garden implements(rakes, shovels, hoes, etc.), and fence postshandled by perspiring workers. Plywood has ahigh salt content and is often targeted byporcupines.

Legal Status

In Wyoming, the porcupine is classified as a“predatory animal” and can be taken without alicense in any manner and at any time of theyear. Many other states have adopted protectivemeasures for porcupines because of theirvulnerability to human harvesting.

Damage Prevention andManagement Techniques

Non-Lethal Techniques

Ecological Methods

Generally, any forest management techniquethat perpetuates closed canopy tree standsreduces porcupine populations. In closedcanopy tree stands there is limited understoryherbaceous vegetation, resulting in reducedfood for porcupines. These conditions restrictporcupine numbers by reducing reproductivepotential, encourage development of largerhome-range areas, and increase winter mortal-ity from stress-related causes due to nutritionaldeficiencies.

Recent theories suggest practices that opencanopy cover, such as prescribed burning andtimber harvest, result in more favorable habitatconditions and attract natural porcupinepredators. Increased predator densities maysuppress porcupine populations as well.Therefore, opinions are mixed regarding thesuccess of ecological methods to controlporcupine populations.

Exclusion

Fencing is a preventive measure with limitedapplication due to the high cost of materials.However, fencing can be cost-effective wherepotential economic losses may be great such asin research areas, commercial tree plantations,and fruit or nut orchards.

Electric fences work best when the smooth hotwire is placed 1½ inches above an 18-inch highpoultry wire fence. For non-electric fences, use12- to 14-gauge woven wire at least 24 inchestall. To discourage climbing, place an overhang-ing wire strip around the top of the fence,facing outward, at a 65 degree angle to thefence top.

To protect mature trees, place a 30 inch wideband of aluminum flashing around the treetrunk to prevent bark chewing at ground level.For small trees, a wire basket that completely

11

encloses the tree works well.

Repellents

Repellents, such as thiram, can be used todiscourage porcupine chewing, although theymust be renewed frequently for maximumeffectiveness. Repellents can be sprayed orpainted on plants targeted by porcupines.

Exterior plywood can be coated with commonwood preservatives to deter chewing, but this isnot 100 percent effective. A better solution isto provide an alternative salt source, sincechewing on plywood is done mainly to satisfy asalt craving. A short picket fence made fromsalt-impregnated wood sticks offers a good “saltlick” for porcupines.

Biological Options

One researcher in the Southwest suggested thatporcupines inflict more damage to trees whenlivestock overgrazing removes preferred sum-mer forage. Assuming this relationship exists,light livestock grazing may be used as a tool tostimulate more herbaceous forage production(used by porcupines as a food source), thereforerelieving porcupine damage to trees in the area.

Enhancing natural predator numbers is anotherbiological control option to consider. Overtime, unrestricted trapping and excessive killingof natural predators, such as the fisher, coyote,and mountain lion, may have promoted higherporcupine numbers. Recently, fishers have beenreleased in California, Idaho, Oregon, Mon-tana, Michigan, Wisconsin, New York, andVermont to re-establish original numbers.These releases were not conducted to controlporcupine populations specifically; however,Michigan researchers report that fishers appearto be impacting porcupine numbers.

Live Trapping

Live trapping porcupines is easy and effectivefor individual animals damaging gardens, small

orchards, or ornamental trees. Commercialcage traps or homemade box traps baited withsalt-soaked materials work well in damageareas. Once trapped, animals should be relo-cated at least 25 miles away in suitable habitatto prevent their return.

Porcupines also can be caught by inverting agarbage can over them, sliding the lid under thecan, and turning the can upright. A coneconstructed of wire fencing material andinverted over the animal works as well. A pieceof plywood can be slid under the wire conebefore inverting the cone. With any live-trapping method, avoid the tail area and usethick rubber gloves to handle the animal.

Lethal TechniquesNon-lethal techniques to control problemporcupines are always the preferred approach.But, in some cases of extensive damage orwhere non-lethal techniques are ineffective onindividual problem animals, lethal controltechniques must be considered.

Shooting

Figure 5. Damage to trees from porcupines commonlyoccurs in the crown where feeding preferences forleaves, terminal twigs, and young bark occurs. (Photocourtesy of Lyle Crosby, retiree, USDA APHIS, AnimalDamage Control, Casper, Wyoming.)

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An effective method of directly controllingporcupine numbers is shooting. Huntingduring late-spring and summer is an effectivetime for harvesting animals feeding on herba-ceous ground vegetation, irrigated crops, andorchard trees. Hunting during the fall and earlywinter may also reduce colonization; however,this usually has less impact on porcupinepopulations than summer shooting.

Poisoning

There are no legally registered toxicants to usein controlling porcupines.

Trapping

Where it is legal, trapping is an effectivetechnique for removing a small number ofanimals, but it is not practical in areas of highporcupine densities. Steel leghold traps, size 2or 3, can be set using salt baits and placed nearthe entrance of active dens or along well-usedtrails. Coyote urine scent posts set near densand in areas of damage activity also are effec-tive. However, non-target animals often aretrapped so leghold sets must be checked dailyto release these animals. Trapped porcupinescan be shot or killed by a sharp blow to thehead. Baits are usually salt-soaked materialssuch as wood blocks, sponges, or clothes.

Summary

Porcupines are interesting animals and play animportant role in ecosystem function. They areone of few animals easily caught by unarmedhumans for use as an emergency food source.Their quills have been used for centuries invarious decorations, while their fur is a valuablecommodity for tying fishing flies. They alsoprovide countless photo opportunities.

Since porcupine activity varies seasonally,specific damage management practices must beadjusted several times each year to provide

optimum damage control. Before implement-ing a damage control technique, assess thepresence of porcupines by looking for brokenquills, fecal piles underneath feeding andresting trees, or characteristic damage signs toarea trees. Select the most efficient, cost-effective damage control technique that iscompatible with the porcupine’s seasonalactivity pattern.

Before implementing extensive control prac-tices, carefully evaluate the degree of damageactually inflicted by porcupines. Total eradica-tion of porcupines from an ecosystem is neithera practical option nor ecologically wise.

Summary of Damage Preventionand Control Methods

Ecological Methods• Implement forest management practices

that perpetuate closed canopy cover toreduce understory forage production (toreduce food supply, encourage larger homeranges and increase stress-related wintermortality).

• Manipulate habitat to attract more naturalpredators.

Exclusion• Fence small areas or areas of potentially

high economic losses with electric or non-electric fencing.

• Place aluminum flashing around maturetree trunks; enclose small trees with wirebaskets.

Repellants• None are specifically registered, although

thiram may repel porcupines.

• Some wood preservatives applied to treesmay provide partial damage relief.

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Biological Options• Light livestock grazing to stimulate herba-

ceous forage used by porcupines as foodsources may reduce damage to area trees.

Shooting• Shooting is most effective during late-

spring and summer activity periods.

Poisoning• There are no legally registered toxicants to

control porcupines at this time.

Trapping• Use steel leghold traps (size 2 or 3) baited

with salt-soaked materials and placed nearactive dens or well-used trails.

• Live trap with commercial cage traps orhomemade box traps baited with salt-soaked materials, then relocate animals atleast 25 miles away.

Other Methods• The best alternative approach to mitigate

damage is to provide alternative salt sourcessuch as salt-impregnated wood.

Acknowledgements

Information presented in this bulletin wasextracted primarily from the following refer-ences:

Brander, R.B. 1973. “Life-history notes on theporcupine in a hardwood-hemlock forestin upper Michigan.” Michigan Academyof Science 5:425-433.

Brockman, S. 1992. “Homeowners guide forresolving wildlife conflicts.” HabitatExtension Bulletin No. 45, Wyoming

Game and Fish Department, Cheyenne,WY.

Costello, D.F. 1966. The world of the porcupine.J.B. Lippincott Company, Philadelphiaand New York.

Curtis, J.D. and E.L. Kozicky. 1944. “Observa-tions on the eastern porcupine.” Journal ofMammology 25:137-146.

Curtis, J.D. and A.K. Wilson. 1953. “ Porcu-pine feeding on ponderosa pine in centralIdaho.” Journal of Forestry 51:339-341.

Dodge, W.E. 1967. “The biology and lifehistory of the porcupine (Erethizondorsatum) in western Massachusetts.”Doctoral dissertation, University ofMassachusetts, Amherst.

Dodge, W.E. 1982. “Porcupine.” In: WildMammals of North America: Biology,Management, and Economics, eds., J.A.Chapman and G.A. Feldhamer, JohnHopkins University Press, Baltimore andLondon, pp. 355-366.

Harder, L.D. 1979. “Winter feeding byporcupines in montane forests of south-western Alberta.” Canadian Field Naturalist93:405-410.

Horn, E.E. 1925. “Studies relative to economiccontrol of porcupines.” USDA ForestService, Southwest Forest and RangeExperiment Station, Flagstaff, AZ. Unpub-lished report, 25 p.

Knopf, A.A. 1989. Audubon society’s field guideto north American mammals. (6th ed.). 520p.

Krefting, L.W., J.H. Stoeckeler, B.J. Bradle,and W.D. Fitzwater. 1962. “Porcupine-timber relationships in the lake states.”Journal of Forestry 60:325-330.

Lawrence, W.H. 1957. Porcupine control: Aresearch analysis. Weyerhaeuser TimberCompany, Centralia, WA.

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MacDonald, D.R. 1952. “Some observationson porcupine attacks on jack pine.” In: TheAnnual Ring, University of Toronto,Canada, pp.17-78.

Murie, O.J. 1926. “The porcupine in northernAlaska.” Journal of Mammology 7:109-113.

Reynolds, H.G. 1957. “Porcupine behavior inthe desert-shrub type of Arizona.” Journalof Mammology 33:418-419.

Roze, U. 1989. The north American porcupine.Smithsonian Institute Press, Washington,D.C.

Roze, U. 1984. “Winter foraging by individualporcupines.” Canadian Journal of Zoology62:2425-2428.

Schemnitz, S.D. 1994. “Porcupines: Damageprevention and control methods.” In:Prevention and Control of Wildlife Damage.Cooperative Extension Service, Universityof Nebraska, Lincoln, pp. B-81 - B-92.

Speer, R.J. and T.G. Dilworth. 1978. “Porcu-pine winter foods and utilization in centralNew Brunswick.” Canadian FieldNaturalist 92:271-274.

Taylor, W.P. 1935. “Ecology and wildlifehistory of the porcupine (Erethizonepixanthum) as related to the forestsof Arizona and southwestern UnitedStates.” Biological Science Bulletin, Univer-sity of Arizona, Tucson, 3:1-177.

Tenneson, C. and L.W. Oring. 1985. “Winterfood preferences of porcupines.” Journal ofWildlife Management 49:28-33.

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