Rodent Complete

7/29/2019 Rodent Complete

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RODENTS

B-1 Beavers James E. Miller and Greg K. Yarrow

B-13 Chipmunks David E. Williams and Robert M. Corrigan

B-17 Gophers, Pocket Ronald M. Case and Bruce A. Jasch

B-31 Mice, House Robert M. Timm

B-47 Mice, White-footed and Deer Robert M. Timm and Walter E. Howard

B-53 Mountain Beavers Dan L. Campbell

B-61 Muskrats James E. Miller

B-71 Nutria Dwight J. LeBlanc

B-81 Porcupines Sanford D. Schemnitz

B-85 Prairie Dogs Scott E. Hygnstrom and Dallas R. Virchow

B-97 Rats, Cotton Donald W. Hawthorne

B-101 Rats, Kangaroo Volney W. Howard, Jr.

B-105 Rats, Norway Robert M. Timm

B-121 Rats, Polynesian Mark E. Tobin

B-125 Rats, Roof Rex E. Marsh

B-133 Woodrats Terrell P. Salmon and W. Paul Gorenzel

B-137 Rodent-proof Construction Rex O. Baker, Robert M. Timm, and Gerald R. Bodman

B-151 Squirrels, Beldings, California, and Rock Ground Rex E. Marsh

B-159 Squirrels, Franklin, Richardson, Columbian, Leonard R. AskhamWashington, and Townsend Ground

B-165 Squirrels, Thirteen-lined Ground Edward C. Cleary and Scott R. Craven

B-171 Squirrels, Tree Jeffrey J. Jackson

B-177 Voles John M. OBrien

B-183 Woodchucks Rene M. Bollengier, Jr.
http://ro_b1.pdf/http://ro_b13.pdf/http://ro_b17.pdf/http://ro_b31.pdf/http://ro_b47.pdf/http://ro_b53.pdf/http://ro_b61.pdf/http://ro_b71.pdf/http://ro_b81.pdf/http://ro_b85.pdf/http://ro_b85.pdf/http://ro_b97.pdf/http://ro_b101.pdf/http://ro_b105.pdf/http://ro_b121.pdf/http://ro_b125.pdf/http://ro_b133.pdf/http://ro_b137.pdf/http://ro_b151.pdf/http://ro_b151.pdf/http://ro_b151.pdf/http://ro_b151.pdf/http://ro_b151.pdf/http://ro_b159.pdf/http://ro_b159.pdf/http://ro_b159.pdf/http://ro_b159.pdf/http://ro_b159.pdf/http://ro_b165.pdf/http://ro_b165.pdf/http://ro_b171.pdf/http://ro_b171.pdf/http://ro_b177.pdf/http://ro_b183.pdf/http://ro_b183.pdf/http://ro_b177.pdf/http://ro_b171.pdf/http://ro_b165.pdf/http://ro_b159.pdf/http://ro_b151.pdf/http://ro_b137.pdf/http://ro_b133.pdf/http://ro_b125.pdf/http://ro_b121.pdf/http://ro_b105.pdf/http://ro_b101.pdf/http://ro_b97.pdf/http://ro_b85.pdf/http://ro_b81.pdf/http://ro_b71.pdf/http://ro_b61.pdf/http://ro_b53.pdf/http://ro_b47.pdf/http://ro_b31.pdf/http://ro_b17.pdf/http://ro_b13.pdf/http://ro_b1.pdf/


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BEAVERSJames E. Miller

Program Leader, Fish and WildlifeUSDA Extension ServiceNatural Resources and Rural

Development UnitWashington, DC 20250

Greg K. Yarrow

Extension Wildlife Specialist

Department of Aquaculture, Fisheries,and WildlifeClemson UniversityClemson, South Carolina 29634-0362

Fig. 1. Beaver, Castor canadensis

Damage Prevention andControl Methods

Exclusion

Fence small critical areas such asculverts, drains, or other structures.

Install barriers around important treesin urban settings.

Cultural Methods and HabitatModification

Eliminate foods, trees, and woodyvegetation where feasible.

Continually destroy dams andmaterials used to build dams.

Install a Clemson beaver pond leveler,three-log drain, or other structuraldevice to maintain a lower pondlevel and avoid further pondexpansion.

Frightening

Shooting of individuals or dynamitingor other continued destruction oflodges, bank dens, and dams,where legal, will occasionally move

young colonies out of an area.

Repellents

None are registered; however, there issome evidence that repellents maybe useful.

Toxicants

None are registered.

Trapping

No. 330 Conibear traps.

Leghold traps No. 3 or larger(including coil-spring types withequivalent jaw spread and impact).

Basket/suitcase type traps areprimarily used for live trapping.

Snares can be useful, particularly indive sets and slides where legal.

ShootingRarely effective (where legal) for

complete control efforts and can bedangerous to humans.

Other Methods

Other methods rarely solve a beaverdamage problem and may increaserisks to humans and nontargetspecies.

PREVENTION AND CONTROL OF WILDLIFE DAMAGE 1994

Cooperative Extension DivisionInstitute of Agriculture and Natural ResourcesUniversity of Nebraska - Lincoln

United States Department of AgricultureAnimal and Plant Health Inspection ServiceAnimal Damage Control

Great Plains Agricultural CouncilWildlife Committee


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B-2

Hind foot

Marks of webs not always distinct

Walking

3" to 6"

Tail mark

Fig. 2. Beaver tracks

Front foot

6"

Fig. 3. A beaver uses its tail as a prop in order tosit upright.

Details of beaver cuttings.

Fig. 4. Range of the beaver in North America.

Identification

The beaver (Castor canadensis, Fig. 1) isthe largest North American rodent.Most adults weigh from 35 to 50pounds (15.8 to 22.5 kg), with someoccasionally reaching 70 to 85 pounds(31.5 to 38.3 kg). Individuals have beenknown to reach over 100 pounds (45

kg). The beaver is a stocky rodentadapted for aquatic environments.Many of the beavers features enable itto remain submerged for long periodsof time. It has a valvular nose and ears,and lips that close behind the fourlarge incisor teeth. Each of the four feethave five digits, with the hind feetwebbed between digits and a splitsecond claw on each hind foot. Thefront feet are small in comparison tothe hind feet (Fig. 2). The underfur is

dense and generally gray in color,whereas the guard hair is long, coarseand ranging in color from yellowishbrown to black, with reddish brownthe most common coloration. Theprominent tail is flattened dorso-ventrally, scaled, and almost hairless.It is used as a prop while the beaver issitting upright (Fig. 3) and for a rudderwhen swimming. Beavers also usetheir tail to warn others of danger byabruptly slapping the surface of thewater.The beavers large front (incisor)

teeth, bright orange on the front, growcontinuously throughout its life. Theseincisors are beveled so that they arecontinuously sharpened as the beavergnaws and chews while feeding,girdling, and cutting trees. The onlyway to externally distinguish the sex ofa beaver, unless the female is lactating,is to feel for the presence of a baculum(a bone in the penis) in males and itsabsence in females.


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Range

Beavers are found throughout NorthAmerica, except for the arctic tundra,most of peninsular Florida, and thesouthwestern desert areas (Fig. 4).The species may be locally abundantwherever aquatic habitats are found.

HabitatBeaver habitat is almost anywherethere is a year-round source of water,such as streams, lakes, farm ponds,swamps, wetland areas, roadsideditches, drainage ditches, canals, minepits, oxbows, railroad rights-of-way,drains from sewage disposal ponds,and below natural springs or artesianwells. Beavers build dams to modifythe environment more to their liking.Dam building is often stimulated by

running water. The length or height ofa dam generally depends upon what isnecessary to slow the flow of waterand create a pond. In areas of flat to-pography, the dam may not be over 36inches (0.9 m) high but as much as 1/4miles (0.4 km) long. In hilly or moun-tainous country, the dam may be 10feet (3 m) high and only 50 feet (15 m)long. Beavers are adaptable and willuse whatever materials are available toconstruct dams fencing materials,bridge planking, crossties, rocks, wire,and other metal, wood, and fiber

materials. Therefore, about the onlyavailable aquatic habitat beavers avoidare those systems lacking acceptablefoods, lodge or denning sites, or a suit-able dam site. Some of the surround-ing timber is cut down or girdled bybeavers to form dams. Subsequentflooding of growing timber causes it todie, and aquatic vegetation soon be-

gins growing. Other pioneer species(for example, willow, sweetgum, andbuttonbush) soon grow around theedges of the flooded area, adding tothe available food supply. The beaverthus helps create its own habitat.

Food Habits

Beavers prefer certain trees andwoody species, such as aspen, cotton-wood, willow, sweetgum, blackgum,black cherry, tulip poplar, and pine,

depending on availability. However,they can and will eat the leaves, twigs,and bark of most species of woodyplants that grow near the water, aswell as a wide variety of herbaceousand aquatic plants. Beavers oftentravel 100 yards (90 m) or more from apond or stream to get to corn fields,soybean fields, and other growingcrops, where they cut the plants off atground level and drag them back tothe water. They eat parts of theseplants and often use the remainder asconstruction material in the dam.

General Biology,Reproduction, andBehavior

Beavers are active for approximately12 hours each night except on thecoldest of winter nights. The phrasebusy as a beaver is appropriate. It is

not uncommon, however, to seebeavers during daylight hours, par-ticularly in larger reservoirs.

Beavers are generally monogamous;copulation may take place either in thewater or in the lodge or bank den.

After a gestation period of about 128days, the female beaver generally givesbirth to 3 or 4 kittens between Marchand June, and nurses them for 6weeks to 3 months. The kittens areborn fully furred with their eyes par-

tially opened and incisors eruptedthrough the gums. They generallybecome sexually mature by the age of1 1/2 years.

Beaver communicate by vocalizations,posture, tail slapping, and scent postsor mud mounds placed around thebank and dam. The beavers castorglands secrete a substance that isdeposited on mud mounds to markterritorial boundaries. These scentposts are found more frequently at

certain seasons, but are found year-round in active ponds.

Fig. 5. Cross section of a beaver lodge.


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Beavers have a relatively long lifespan, with individuals known to havelived to 21 years. Most, however, donot live beyond 10 years. The beaver isunparalleled at dam building and canbuild dams on fast-moving streams aswell as slow-moving ones. They alsobuild lodges and bank dens, depend-ing on the available habitat. All lodges

and bank dens have at least two en-trances and may have four or more.The lodge or bank den is used prima-rily for raising young, sleeping, andfood storage during severe weather(Fig. 5).

The size and species of trees the beavercuts is highly variable from a 1-inch(2.5-cm) diameter at breast height(DBH) softwood to a 6-foot (1.8-m)DBH hardwood. In some areas bea-vers usually cut down trees up toabout 10 inches (25 cm) DBH andmerely girdle or partially cut largerones, although they often cut downmuch larger trees. Some beavers seemto like to girdle large pines and sweet-gums. They like the gum or storax thatseeps out of the girdled area of sweet-gum and other species.

An important factor about beavers istheir territoriality. A colony generallyconsists of four to eight related bea-vers, who resist additions or outsidersto the colony or the pond. Young bea-

vers are commonly displaced from thecolony shortly after they become sexu-ally mature, at about 2 years old. Theyoften move to another area to begin anew pond and colony. However, somebecome solitary hermits inhabiting oldabandoned ponds or farm ponds ifavailable.

Beavers have only a few natural preda-tors aside from humans, includingcoyotes, bobcats, river otters, andmink, who prey on young kittens. In

other areas, bears, mountain lions,wolves, and wolverines may prey onbeavers. Beavers are hosts for severalectoparasites and internal parasites in-cluding nematodes, trematodes, andcoccidians. Giardia lamblia is a patho-genic intestinal parasite transmitted bybeavers, which has caused humanhealth problems in water supply sys-

Fig. 6. Pine plantation in Arkansas killed in flooding caused by beavers.

tems. The Centers for Disease Controlhave recorded at least 41 outbreaks ofwaterborne Giardiasis, affecting morethan 15,000 people. For more informa-tion about Giardiasis, see vonOettingen (1982).

Damage and DamageIdentification

The habitat modification by beavers,caused primarily by dam building, isoften beneficial to fish, furbearers,reptiles, amphibians, waterfowl, andshorebirds. However, when this modi-fication comes in conflict with humanobjectives, the impact of damage mayfar outweigh the benefits.

Most of the damage caused by beaversis a result of dam building, bank bur-rowing, tree cutting, or flooding. Somesoutheastern states where beaver dam-

age is extensive have estimated thecost at $3 million to $5 million dollarsannually for timber loss; crop losses;roads, dwellings, and flooded prop-erty; and other damage. In somestates, tracts of bottomland hardwoodtimber up to several thousand acres(ha) in size may be lost because of bea-ver. Some unusual cases observed

include state highways floodedbecause of beaver ponds, reservoirdams destroyed by bank den burrowscollapsing, and train derailmentscaused by continued flooding and bur-rowing. Housing developments havebeen threatened by beaver dam flood-ing, and thousands of acres (ha) ofcropland and young pine plantationshave been flooded by beaver dams(Fig. 6). Road ditches, drain pipes, andculverts have been stopped up sobadly that they had to be dynamitedout and replaced. Some bridges havebeen destroyed because of beaverdam-building activity. In addition,beavers threaten human health bycontaminating water supplies withGiardia.

Identifying beaver damage generally isnot difficult. Signs include dams;dammed-up culverts, bridges, or drainpipes resulting in flooded lands, tim-

ber, roads, and crops; cut-down orgirdled trees and crops; lodges andburrows in ponds, reservoir levees,and dams. In large watersheds, it maybe difficult to locate bank dens. How-ever, the limbs, cuttings, and debrisaround such areas as well as damsalong tributaries usually help pinpointthe area.


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Legal Status

The legal status of beavers varies fromstate to state. In some states the beaveris protected except during furbearerseasons; in others it is classified as apest and may be taken year-roundwhen causing damage. Because of itsfur value, dam building, and resulting

water conservation, it is generally notconsidered a pest until economiclosses become extensive. Fur prices forbeaver in some states, particularly inthe Southeast, make it hardly worththe skinning and stretching. In somenorthern states, trapping is prohibitednear lodges or bank dens to protectand perpetuate beaver colonies. Furprices for beaver pelts are usuallymuch higher in these areas.


Exclusion

It is almost impossible as well as cost-prohibitive to exclude beavers fromponds, lakes, or impoundments. If theprimary reason for fencing is toexclude beavers, fencing of large areasis not practical. Fencing of culverts,drain pipes, or other structures cansometimes prevent damage, but fenc-

ing can also promote damage, since itprovides beavers with constructionmaterial for dams. Protect valuabletrees adjacent to waterways by encir-cling them with hardware cloth,woven wire, or other metal barriers.Construction of concrete spillways orother permanent structures mayreduce the impact of beavers.

Cultural Methods

Because beavers usually alter ormodify their aquatic habitat so exten-sively over a period of time, mostpractices generally thought of as cul-tural have little impact on beavers.Where feasible, eliminate food, trees,and woody vegetation that is adjacentto beaver habitat. Continual destruc-tion of dams and removal of damconstruction materials daily will(depending on availability of construc-tion materials) sometimes cause a

colony or individual beavers to moveto another site. They might, however,be even more troublesome at the newlocation.

The use of a three-log drain or a struc-tural device such as wire mesh cul-verts (Roblee 1983) or T-culvert guards(Roblee 1987) will occasionally causebeavers to move to other areas. They

all prevent beavers from controllingwater levels. However, once beavershave become abundant in a watershedor in a large contiguous area, periodicreinvasions of suitable habitat can beexpected to occur. Three-log drainshave had varying degrees of success incontrolling water levels in beaver im-poundments, especially if the beavercan detect the sound of falling water orcurrent flow. All of these devices willstimulate the beavers to quickly plugthe source of water drainage.

A new device for controlling beaverimpoundments and keeping blockedculverts open is the Clemson beaverpond leveler. It has proven effective inallowing continual water flow in previ-ously blocked culverts/drains andfacilitating the manipulation of waterlevels in beaver ponds for moist-soilmanagement for waterfowl (Woodand Woodward 1992) and other envi-ronmental or aesthetic purposes. Thedevice (Fig. 7) consists of a perforated

PVC pipe that is encased in heavy-gauge hog wire. This part is placedupstream of the dam or blocked cul-vert, in the main run or deepest part ofthe stream. It is connected to nonper-forated sections of PVC pipe which arerun through the dam or culvert to awater control structure downstream. Itis effective because the beavers cannotdetect the sound of falling or flowingwater as the pond or culvert drains;therefore, they do not try to plug thepipe. The Clemson beaver pond lev-eler works best in relatively flat terrainwhere large volumes of water fromwatersheds in steep terrain are not aproblem.

Repellents

There are no chemical repellents regis-tered for beavers. Past research effortshave tried to determine the effective-

ness of potential repellent materials;however, none were found to be effec-tive, environmentally safe, or practical.One study in Georgia (Hicks 1978)indicated that a deer repellent hadsome potential benefit. Other studieshave used a combination of dam blow-ing and repellent soaked (Thiram 80and/or paradichlorobenzene) rags to

discourage beavers with varyingdegrees of success (Dyer and Rowell1985).

Additional research is needed onrepellents for beaver damage preven-tion.

Toxicants

None are registered. Research effortshave been conducted, however, to findeffective, environmentally safe andpractical toxicants. Currently there are

none that meet these criteria.

Fumigants

None are registered.

Trapping

The use of traps in most situationswhere beavers are causing damage isthe most effective, practical, and envi-ronmentally safe method of control.The effectiveness of any type of trapfor beaver control is dependent on the

trappers knowledge of beaver habits,food preferences, ability to read beaversigns, use of the proper trap, and trapplacement. A good trapper with adozen traps can generally trap all thebeavers in a given pond (behind onedam) in a week of trap nights. Obvi-ously in a large watershed with severalcolonies, more trapping effort will berequired. Most anyone with trappingexperience and some outdoor savvycan become an effective beaver trapperin a short time. In an area where bea-

vers are common and have not beenexposed to trapping, anyone experi-enced in trapping can expect good suc-cess. Additional expertise andimproved techniques will be gainedthrough experience.

A variety of trapping methods andtypes of traps are effective for beavers,depending on the situation. Fish andwildlife agency regulations vary from


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B-6

Elbow and stand pipe are optional.Needed only to manage water level ifmaintaining pond is an objective.

1" re-bar6' long

8" diameter 40 PVC pipe

T - joint tilted with a drain plugmay replace elbow.

Pond side

20'

Table 1. List of materials for the Clemson Beaver Pond Leveler.

Quantity Item

1 .......... .......... ........... ... 10' section, 10" diameter PVC pipe (Schedule 40)1 .......... .......... ........... ... PVC cap for 10" diameter PVC pipe (Schedule 40)1 .......... .......... ........... ... 10" x 8" PVC pipe reducer coupling (Schedule 40)4 .......... .......... ........... ... 86" sections, 3/4" diameter plastic roll pipe (water pipe), 160 psi grade4 .......... .......... ........... ... 3/4" metal couplings for roll pipe

16 .......... .......... ........... ... 1/4" x 2" galvanized eyebolts16 .......... .......... ........... ... 1/4" galvanized nuts16 .......... .......... ........... ... 1/4" galvanized washers16 .......... .......... ........... ... 16" sections, 8 gauge galvanized wire (medium hardness)2 .......... .......... ........... ... 96" sections, 2" x 4" 1/2 gauge galvanized welded wire

2 lbs ........... ........... .......... .. Crab trap clamps (fasteners)

The above materials are required to assemble the intake device. The carrying pipe (flow pipe) may consist of 20 to 40 feet of8-inch diameter PVC, Schedule 40 with coupling sleeves and elbows appropriate to the desired configuration.

Fig. 7. Clemson beaver pond leveler.

state to state. Some types of traps andtrapping methods, although effectiveand legal in some states, may beprohibited by law in other states.Individual state regulations must bereviewed annually before beginning atrapping program

In some states where beavers havebecome serious economic pests, specialregulations and exemptions have beenpassed to allow for increased controlefforts. For example, some states allowtrapping and snaring of beavers andother control measures throughout the

year. Others, however, prohibit trap-ping except during established furtrapping seasons. Some states allowexemptions for removal of beaversonly on lands owned or controlled bypersons who are suffering losses. Insome states a special permit isrequired from the state fish and wild-life agency.

Of the variety of traps commonlyallowed for use in beaver control, theConibear type, No. 330, is one of themost effective (Fig. 8). Not all trapperswill agree that this type of trap is the

most effective; however, it is the typemost commonly used by professionaltrappers and others who are princi-pally trapping beavers. This trap killsbeavers almost instantly. When prop-erly set, the trap also prevents anyescape by a beaver, regardless of itssize. Designed primarily for water use,it is equally effective in deep and shal-low water. Only one trap per site isgenerally necessary, thus reducing theneed for extra traps. The trap exertstremendous pressure and impactwhen tripped. Appropriate care mustbe exercised when setting and placing

Intakedevice

Beaverdam


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the trap. Care should also be takenwhen using the Conibear type trapsin urban and rural areas where pets(especially dogs) roam free. Use trapsets where the trap is placed com-pletely underwater.

Some additional equipment will beuseful: an axe, hatchet, or large cuttingtool; hip boots or waders; wire; andwire cutters. With the Conibear-typetrap, some individuals use a device or

tool called setting tongs. Others usea piece of 3/8- or 1/2-inch (9- or 13-mm) nylon rope. Most individualswho are experienced with these trapsuse only their hands. Regardless of thetechniques used to set the trap, careshould be exercised.

Earlier models of the Conibear typeof trap came with round, heavy steelcoils which were dangerous to handleunless properly used in setting the

trap. They are not necessary to safelyset the trap. However, the two safetyhooks, one on each spring, must becarefully handled as each spring isdepressed, as well as during trapplacement. On newer models an addi-tional safety catch (not attached to thesprings) is included for extra precau-tion against inadvertent spring release.

The last step before leaving a set trap isto lift the safety hook attached to eachspring and slide the safety hook backfrom the trap toward the spring eye,making sure to keep hands and feetsafely away from the center of the trap.If the extra (unattached) safety catch isused, it should be removed before thesafety hooks that are attached to thesprings to keep it from getting in theway of the movement of the safetyhooks.

Conibear-type traps are best set whileon solid ground with dry hands. Oncethe springs are depressed and thesafety hooks in place, the trap or trapscan be carried into the water forproper placement. Stakes are neededto anchor the trap down. In most bea-ver ponds and around beaver dams,plenty of suitable stakes can be found.At least two strong stakes, preferablystraight and without forks or snags,should be chosen to place througheach spring eye (Fig. 8). Additional

stakes may be useful to put betweenthe spring arms and help hold the trapin place. Do not place stakes on theoutside of spring arms. Aside fromserving to hold the trap in place, thesestakes also help to guide the beaverinto the trap. Where needed, they arealso useful in holding a dive stick at orjust beneath the water surface (Fig. 9).If necessary, the chain and circleattached to one spring eye can beattached to another stake. In deepwater sets, a chain with an attached

wire should be tied to something at orabove the surface so the trapper canretrieve the trap. Otherwise the trapmay be lost.

Trap Sets. There are many sets that canbe made with a Conibear-type trap(for example, dam sets, slide sets,lodge sets, bank den sets, run/trailsets, under log/dive sets, pole sets,under ice sets, deep water sets, drain

Fig. 8. Basic method of setting and staking aConibear 330 trap. Additional stakes arenormally used (see Fig. 9).

Dive stick

Fig. 9. Conibear trap in dive set.

Run

Levee

EntranceFig. 10. Runs or underwater entrances to lodgesare good places to set beaver traps.


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B-8

pipe sets), depending on the trapperscapability and ingenuity. In many bea-ver ponds, however, most beavers canbe trapped using dam sets, lodge orbank den sets, sets in runs/trails,dive sets or sets in slides entering thewater from places where beavers arefeeding. Beavers swim both at the sur-face or along the bottom of ponds, de-

pending on the habitat and waterdepth. Beavers also establish runs ortrails which they habitually use in trav-eling from lodge or den to the dam orto feeding areas, much like cow trailsin a pasture.

Place traps directly across these runs,staked to the bottom (Fig. 10).

Use a good stake or walking staffwhen wading in a beaver pond tolocate deep holes, runs, or trails. Thiswill prevent stepping off over waders

or hip boots in winter, and will helpward off cottonmouth snakes in thesummer. The staff can also help locategood dive holes under logs as youwalk out runs or trails. In older beaverponds, particularly in bottomlandswamps, it is not uncommon to findruns and lodge or bank den entranceswhere the run or hole is 2 to 3 feet (0.6to 0.9 m) below the rest of the im-poundment bottom.

To stimulate nighttime beaver move-

ment, tear a hole in a beaver dam andget the water moving out of a pond.Beavers quickly respond to the soundof running water as well as to the cur-rent flow. Timing is also important ifyou plan to make dam sets. Open ahole in the dam about 18 inches to 2feet (46 to 60 cm) wide and 2 to 3 feet(60 to 90 cm) below the water level onthe upper side of the dam in the morn-ing. This will usually move a substan-tial amount of water out of the pondbefore evening (Fig. 11). Set traps in

front of the dam opening late thatsame evening. Two problems can ariseif you set a trap in the morning as soonas a hole is made: (1) by late evening,when the beavers become active, thetrap may be out of the water and inef-fective; or (2) a stick, branch, or otherdebris in the moving water may tripthe trap, again rendering it ineffective.

Fig. 11. Dam set. Set the trap underwater infront of the hole created in the dam. When thebeaver returns to patch the hole, it will becaught in the trap.

Hole torn through dam to release water.

Beaver dam

Fig. 12. Leghold trap (No. 3 or No. 4, doublespring) attached to wire for drowning set.

Dig out slide under water to accept trap andsprings.

Slide wire fastened tostake and weight.

Fig. 13. Leghold trap in slide set.


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The best dam sets are made about 12to 18 inches (30.8 to 45.7 cm) in front ofthe dam itself. Using stakes or debrison either side of the trap springs,create a funnel to make the beaver gointo the jaws of the trap. Always setthe trigger on the Conibear-type trapin the first notch to prevent debrisfrom tripping it before the beaver

swims into the trap. The two heavy-gauge wire trippers can be bent out-ward and the trigger can be set awayfrom the middle if necessary, to keepdebris from tripping the trap. This canalso keep small beaver or possibly fishor turtles from springing the trap.

Double-spring leghold traps have beenused for hundreds of years and arestill very effective when properly usedby skilled trappers. Use at least No. 3double (long) spring or coil spring typeleghold traps or traps of equivalentsize jaw spread and strength. Use adrowning set attachment with anyleghold trap (Fig. 12). As the traps aretripped, the beaver will head for thewater. A weight is used to hold thetrapped beaver underwater so that itultimately drowns. Some trappersstake the wire in deep water to accom-plish drowning. If leghold traps arenot used in a manner to accomplishdrowning, there is a good likelihoodthat legs or toes will be twisted off or

pulled loose, leaving an escaped, trap-wise beaver.

Placement is even more critical withleghold traps than with the Conibear-type. Place leghold traps just at thewaters edge, slightly underwater,with the pan, jaws, and springs cov-ered lightly with leaves or debris orpressed gently into the pond bottom insoft mud. Make sure there is a cavityunder the pan so that when thebeavers foot hits the pan, it will trig-ger the trap and allow the jaws to snapclosed. Place traps off-center of thetrail or run to prevent belly pinchingor missing the foot or leg. With someexperience, beaver trappers learn tomake sets that catch beavers by a hindleg rather than a front leg. The frontleg is much smaller and easier to twistoff or pull out.

Sometimes its wise, when usingleghold traps, to make two sets in aslide, run, dam, or feeding place toincrease trapping success and removebeavers more quickly. In some situa-tions, a combination of trappingmethods can shorten trapping timeand increase success.

Trappers have come up with unique

methods of making drown sets. One ofthe simplest and most practical is aslide wire with a heavy weightattached to one end, or with an endstaked to the bottom in 3 or more feet(>0.9 m) of water. The other end of thewire is threaded through a hole in oneend of a small piece of angle iron. Thetrap chain is attached to a hole in theother end of the angle. The end of thewire is then attached to a tree or stakedriven into the bank (Fig. 13). Whenthe beaver gets a foot or leg in the trap,it immediately dives back into thewater. As the angle slides down thewire, it prevents the beaver fromreaching the surface. The angle ironpiece will not slide back up the wireand most often bends the wire as thebeaver struggles, thus preventing thebeaver from coming up for air. Trap-pers should be prepared to quicklyand humanely dispatch a beaver thatis caught in a trap and has notdrowned.

The leghold trap set in lodges or bankdens is also effective, especially fortrapping young beavers. Place the seton the edge of the hole where the bea-ver first turns upward to enter thelodge or den, or place it near the bot-tom of the dive hole. Keep the jawsand pan off of the bottom by pullingthe springs backward so that a swim-ming foot will trip the pan. Stake theset close to the bottom or wire the trapto a log or root on the bottom, to avoidthe need for drowning weights, wires,and angle iron pieces. Generally, moretime and expertise is necessary tomake effective sets with leghold trapsand snares than is required with theConibear-type trap.

Use scent or freshly cut cottonwood,aspen, willow, or sweetgum limbs toentice beaver to leghold trap sets. Baitor scent is especially useful aroundscent mounds and up slides along thebanks or dams. Most trappers who useConibear-type traps do not employbaits or scent, although they are occa-sionally helpful. In some states it is ille-

gal to use bait or scent.Several other types of traps can beused, including basket/suitcase typelive traps. These are rarely used, how-ever, except by professionals in urbanareas where anti-trap sentiment orother reasons prevent the killing ofbeavers. These traps are difficult andcumbersome to use, and will not befurther discussed here for use in bea-ver damage control. Any type of trapsused for beavers or other animalsshould be checked daily.

Snaring can be a very cost-effectivemethod for capturing beavers. Snaringequipment costs far less than trappingequipment and is more convenient touse in many situations. In addition,beavers can be captured alive by snar-ing and released elsewhere if desired.

Snare placement is similar to trapplacement. First, look for runways andfresh sign that indicate where beaveractivities are focused. Find a suitable

anchor such as a large tree, log, or rootwithin 10 feet (3 m) of the runwaywhere the snare will be set. If neces-sary, anchor snares by rods driven intothe ground, but this is more time con-suming and less secure. Attach three14-gauge wires to the anchor so thateach can swivel freely. Cut each wireto length so they reach about 1 foot (30cm) past the runway. Twist the wirestogether to form a strong braidedanchor cable. Drive a supporting stakeinto the ground near the runway and

wrap the free end of the anchor cablearound it twice. Prepare a new, dyed,No. 4 beaver or coyote snare, consist-ing of 42 inches (107 cm) of 3/32-inch(2.4-mm) steel cable with an attachedwire swivel and slide lock. Twist thefree ends of the three anchor wiresaround the wire swivel on the end of


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the snare cable. Wrap the longest an-chor wire around the base of the wireswivel and crimp it onto the snarecable about 2 inches (5 cm) from theswivel. Use both the stake and the sup-porting anchor wire to suspend a full-sized loop about 4 inches (10 cm)above the runway. If necessary, useguide sticks or other natural debris to

guide beaver into the snare.The described snare set is very com-mon, but there are several variationsand sets that can be used. Snares arefrequently placed under logs, nearbank dens, and next to castor mounds.Drowning sets can be made using un-derwater anchors, slide cables, andslide locks.

Snares should be checked at least ev-ery 24 hours. Dispatch snared beaverswith a sharp blow or shot to the head.

Beavers can be chemically immobi-lized and transported to suitable sitesfor release if desired.

Snares must be used with great care toavoid capturing nontarget animals.Avoid trails or areas that are used bylivestock, deer, or dogs. Check withyour local wildlife agency for regula-tions associated with trapping andsnaring. Snaring is not allowed insome states.

For more information about the use of

snares seeA Guide to Using Snares forBeaver Capture (Weaver et al. 1985)listed at the end of this chapter.

Shooting

In some states, because of the extent ofdamage caused by beavers, regula-tions have been relaxed to allow shoot-ing. Some states even allow the use ofa light at night to spot beavers whileshooting. Before attempting to shootbeavers, check regulations, and if

applicable, secure permits and notifylocal law enforcement personnel ofyour intentions.

Beavers are most active from late after-noon to shortly after daybreak,depending on the time of year. Theyusually retire to a lodge or bank denfor the day. Therefore, if night shoot-ing is not permitted, the early eveningand early morning hours are most

productive. Choice of weaponsdepends on the range and situation.Most shooting is done with a shotgun

at close range at night. Shooting aloneis generally not effective in eliminatingall beaver damage in an area. It can,however, be used to quickly reduce apopulation.

Other Methods

Because of the frustration and damagebeavers have caused landowners,almost every control method imagin-able has been tried. These range fromdynamiting lodges during midday to

using snag-type fish hooks in front ofdams, road culverts, and drain pipes.Such methods rarely solve a damageproblem, although they may kill a fewbeavers and nontarget species. Theyare not recommended by responsiblewildlife professionals. One methodused occasionally along streams proneto flooding is shooting beavers thathave been flooded out of lodges andbank dens. This method is often dan-gerous and rarely solves a damageproblem.

Economics of Damageand Control

The economics of beaver damage issomewhat dependent on the extent ofthe damage before it has been dis-covered. Some beaver damage prob-lems are intensive, such as damage

caused by one or two beavers in a newpond, damming or stopping up a cul-vert or drain pipe, flooding roads, or

crops. Other problems are extensive,such as several beaver colonies in aflatland area, responsible for the flood-ing of several hundred acres of mar-ketable timber that will die unless thewater is removed quickly. Generallyspeaking, if a culvert or drain pipe canbe unstopped, a knowledgeable trap-per can remove one or two beavers ina night or two and eliminate furtherdamage in an intensive damage situa-tion (Fig. 14). However, an extensivesituation may require a concentrated

effort with several trappers,dynamiting or pulling dams, and amonth or more of trapping to get thewater off the timber and reduce fur-ther timber losses.

Economic damage is estimated to haveexceeded $40 billion in the South-eastern United States during a recent40-year period (Arner and Dubose1982). This would include all damageto crops, forests, roads, pastures, andother rural and urban properties.

Economically, one must assess thesituation and weigh the tradeoffs: thepotential loss of thousands of boardfeet of timber and years of regenera-tion versus the cost of trapping. Thecost of a couple of nights trapping anda half-day of labor to clear the culvertsis much less than the cost of rebuildinga washed-out road or losing floodedcrops or timber.

Fig. 14. Conibear in culvert set. When beaversare stopping up a drainage culvert, (1) clean outthe pipe to get water flowing through freely; (2)set the trap at the level of the drain pipeentrance, but far enough away to clear theculvert when the beaver enters; (3) put stakeson either side to make the beaver enter the trapcorrectly.


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The most important point is that dam-age control should begin as soon as itis evident that a beaver problem existsor appears likely to develop. Once bea-ver colonies become well establishedover a large contiguous area, achievingcontrol is difficult and costly. One ofthe most difficult situations ariseswhen an adjacent landowner will not

allow the control of beavers on theirproperty. In this situation, one canexpect periodic reinvasions of beaversand continual problems with beaverdamage, even if all beavers areremoved from the property wherecontrol is practiced.

Although benefits of beavers and bea-ver ponds are not covered in depthhere, there are a number. Aside fromcreating fish, waterfowl, furbearer,shorebird, reptile, and amphibian habi-tat, the beaver in many areas is animportant fur resource, as well as afood resource. For those who have notyet tried it, beaver meat is excellenttable fare if properly prepared, and itcan be used whether the pelts areworth skinning or not. It also makesgood bait for trapping large predators.

Proper precautions, such as wearingrubber gloves, should be taken whenskinning or eviscerating beaver car-casses, to avoid contracting transmis-sible diseases such as tuleremia.

Acknowledgments

The authors thank, for their cooperation, pastand present employees of the Fish and WildlifeService, US Department of the Interior, countyextension agents with the CooperativeExtension Service in various states, cooperatorswith the USDA-APHIS-ADC program in anumber of states, and the many landownerswith beaver problems across the South. Theexperience gained in efforts to assist landowners

with wildlife damage problems provided mostof the information contained herein.

Figures 1, 2, 4 and 5 from Schwartz andSchwartz (1981).

Figure 3 by Jill Sack Johnson.

Figure 6 and 7 by the authors.

Figures 8 through 12 and 14 from Miller (1978).

Figure 13 by Jill Sack Johnson after Miller (1978).

For AdditionalInformation

Arner, D. H., and J. S. Dubose. 1982. The impactof the beaver on the environment andeconomics in Southeastern United States.Trans. Int. Congr. Game Biol. 14:241-247.

Byford, J. L. 1976. Beavers in Tennessee: control,utilization and management. TennesseeCoop. Ext. Serv., Knoxville. Pub. 687. 15 pp.

Dyer, J. M., and C. E. Rowell. 1985. Aninvestigation of techniques used todiscourage rebuilding of beaver damsdemolished by explosives. Proc. EasternWildl. Damage Control Conf. 2:97-102.

Hicks, J. T. 1978. Methods of beaver control.Final Rep., Res. Proj. No. W-37-R, GeorgiaGame Fish Div., Dep. Nat. Res. 3 pp.

Hill, E. H. 1974. Trapping beaver and processingtheir fur. Alabama Coop. Wildl. Res. Unit,Agric. Exp. Stn., Auburn Univ. Pub. No. 1.10 pp.

Miller, J. E. 1972. Muskrat and beaver control.

Proc. Nat. Ext. Wildl. Workshop, 1:35-37.

Miller, J. E. 1978. Beaver friend or foe.Arkansas Coop. Ext. Serv., Little Rock. Cir.539. 15 pp.

Roblee, K. J. 1983. A wire mesh culvert for use incontrolling water levels at nuisance beaversites. Proc. Eastern Wildl. Damage ControlConf. 1:167-168.

Roblee, K. J. 1987.The use of the T-culvert guardto protect road culverts from pluggingdamage by beavers. Proc. Eastern Wildl.Damage Control Conf. 3:25-33

Schwartz, C. W., and E. R. Schwartz. 1981. Thewild mammals of Missouri, Rev. ed. Univ.Missouri Press, Columbia. 356 pp.

von Oettingen, S.L. 1982. A survey of beaver incentral Massachusetts forGiardia lamblia.M.S. Thesis, Univ. Massachusetts, Amherst.58 pp.

Weaver, K. M., D. H. Arner, C. Mason, and J. J.Hartley. 1985. A guide to using snares forbeaver capture. South. J. Appl. For. 9(3):141-146.

Wood, G. W., and L. A. Woodward. 1992. TheClemson beaver pond leveler. Proc. Annu.Conf. Southeast Fish Wildl. Agencies.

EditorsScott E. HygnstromRobert M. TimmGary E. Larson


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CHIPMUNKS

Fig. 1. Eastern chipmunk, Tamias striatus

David E. Williams

State DirectorUSDA-APHIS-Animal Damage ControlLincoln, Nebraska 68501

Robert M. Corrigan

Staff SpecialistVertebrate Pest Management

Purdue UniversityWest Lafayette, Indiana 47907


Exclusion

Rodent-proof construction willexclude chipmunks from structures.

Use 1/4-inch (0.6-cm) mesh hardwarecloth to exclude chipmunks fromgardens and flower beds.

Habitat Modification

Store food items, such as bird seedand dog food, in rodent-proofcontainers.

Ground covers, shrubs, and wood pilesshould not be located adjacent tostructure foundations.

Frightening

Not effective.

Repellents

Area repellents. Naphthalene (mothflakes or moth balls) may be effec-tive if liberally applied in confinedplaces.

Taste repellents. Repellents containingbitrex, thiram, or ammonium soapsof higher fatty acids applied toflower bulbs, seeds, and vegetation(not for human consumption) maycontrol feeding damage.

Toxicants

None are federally registered. Check

with local extension agents or aUSDA-APHIS-ADC personnel forpossible Special Local Needs 24(c)registrations.

Fumigants

Generally impractical.

Trapping

Rat-sized snap traps.

Live (box or cage) traps.

Glue boards.

Shooting

Small gauge shotguns or .22-caliberrifles.






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Identification

Fifteen species of native chipmunks ofthe genus Eutamias and one of thegenus Tamias are found in NorthAmerica. The eastern chipmunk(Tamias striatus) and the least chip-munk (Eutamias minimas), discussedhere, are the two most widely distrib-

uted and notable species. Behavior anddamage is similar among all species ofnative chipmunks. Therefore, damagecontrol recommendations are similarfor all species.

The eastern chipmunk is a small,brownish, ground-dwelling squirrel. Itis typically 5 to 6 inches (13 to 15 cm)long and weighs about 3 ounces (90 g).It has two tan and five blackish longi-tudinal stripes on its back, and two tanand two brownish stripes on each side

of its face. The longitudinal stripes endat the reddish rump. The tail is 3 to 4inches (8 to 10 cm) long and hairy, butit is not bushy (Fig. 1).

The least chipmunk is the smallest ofthe chipmunks. It is typically 3 2/3 to4 1/2 inches (9 to 11 cm) long andweighs 1 to 2 ounces (35 to 70 g). Thecolor varies from a faint yellowish graywith tawny dark stripes (Badlands,South Dakota) to a grayish tawnybrown with black stripes (Wisconsin

and Michigan). The stripes, however,continue to the base of the tail on allleast chipmunks.

Chipmunks are often confused withthirteen-lined ground squirrels(Spermophilus tridecemlineatus), alsocalled striped gophers, and redsquirrels (Tamiasciurus hudsonicus). Thethirteen-lined ground squirrel is yel-lowish, lacks the facial stripes, and itstail is not as hairy as the chipmunks.As this squirrels name implies, it has13 stripes extending from the shoulderto the tail on each side and on its back.When startled, a ground squirrel car-ries its tail horizontally along theground; the chipmunk carries its tailupright. The thirteen-lined groundsquirrels call sounds like a high-pitched squeak, whereas chipmunkshave a rather sharp chuck-chuck-chuck call. The red squirrel is very vo-cal and has a high-pitched chatter. It is

Chipmunks are generally solitary ex-cept during courtship or when rearingyoung.

The least chipmunk inhabits low sage-brush deserts, high mountain conifer-ous forests, and northern mixedhardwood forests.

The home range of a chipmunk may

be up to 1/2 acre (0.2 ha), but the adultonly defends a territory about 50 feet(15.2 m) around the burrow entrance.Chipmunks are most active during theearly morning and late afternoon.

Chipmunk burrows often are well-hidden near objects or buildings (forexample, stumps, wood piles or brushpiles, basements, and garages). Theburrow entrance is usually about 2inches (5 cm) in diameter. There are noobvious mounds of dirt around the en-trance because the chipmunk carriesthe dirt in its cheek pouches and scat-ters it away from the burrow, makingthe burrow entrance less conspicuous.

In most cases, the chipmunks maintunnel is 20 to 30 feet (6 m to 9 m) inlength, but complex burrow systemsoccur where cover is sparse. Burrowsystems normally include a nestingchamber, one or two food storagechambers, various side pockets con-nected to the main tunnel, and sepa-rate escape tunnels.

With the onset of cold weather, chip-munks enter a restless hibernation andare relatively inactive from late fallthrough the winter months. Chip-munks do not enter a deep hibernationas do ground squirrels, but rely on thecache of food they have brought totheir burrow. Some individuals be-come active on warm, sunny days dur-ing the winter. Most chipmunksemerge from hibernation in earlyMarch.

Eastern chipmunks mate two times ayear, during early spring and againduring the summer or early fall. Thereis a 31-day gestation period. Two to 5young are born in April to May andagain in August to October. The youngare sexually mature within 1 year.Adults may live up to 3 years.

larger than the chipmunk, has a

bushier tail and lacks the longitudinalstripes of the chipmunk. Red squirrelsspend a great deal of time in trees,while chipmunks spend most of theirtime on the ground, although they canclimb trees.

Range

The eastern chipmunks range in-cludes most of the eastern UnitedStates. The least chipmunks rangeincludes most of Canada, the US

Rocky Mountains, the Great Basin, andparts of the upper Midwest (Fig. 2).

Habitat and GeneralBiology

Eastern chipmunks typically inhabitmature woodlands and woodlot edges,but they also inhabit areas in andaround suburban and rural homes.

a

b

Fig. 2. Range of the eastern (a) and least chip-munk (b) in North America.


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Adult least chipmunks mate over aperiod of 4 to 6 weeks from April tomid-July. Least chipmunks produce 1litter of 2 to 7 young in May or June.Occasionally a second litter is pro-duced in the fall.

Chipmunk pups appear above groundwhen they are 4 to 6 weeks old 2/3the size of an adult. Young will leave

the burrow at 6 to 8 weeks.

Population densities of chipmunks aretypically 2 to 4 animals per acre (5 to10/ha). Eastern chipmunk populationdensities may be as high as 10 animalsper acre (24/ha), however, if sufficientfood and cover are available. Homeranges often overlap amongindividuals.

Food Habits

The diet of chipmunks consists prima-rily of grains, nuts, berries, seeds,mushrooms, insects, and carrion.Although chipmunks are mostlyground-dwelling rodents, they regu-larly climb trees in the fall to gathernuts, fruits, and seeds. Chipmunkscache food in their burrows through-out the year. By storing and scatteringseeds, they promote the growth ofvarious plants.

Chipmunks also prey on young birds

and bird eggs. Chipmunks themselvesserve as prey for several predators.


Throughout their North Americanrange, chipmunks are considered mi-nor agricultural pests. Most conflictswith chipmunks are nuisance prob-lems. When chipmunks are present inlarge numbers they can cause struc-tural damage by burrowing under

patios, stairs, retention walls, or foun-dations. They may also consumeflower bulbs, seeds, or seedlings, aswell as bird seed, grass seed, and petfood that is not stored in rodent-proofstorage containers. In New England,chipmunks and tree squirrels causeconsiderable damage to maple sugartubing systems by gnawing the tubes.

Legal Status

Chipmunks are not protected by fed-eral law, but state and local regulationsmay apply. Most states allow land-owners or tenants to take chipmunkswhen they are causing or about tocause damage. Some states, (forexample, Georgia, North Carolina, andArkansas) require a permit to killnongame animals. Other states arecurrently developing laws to protectall nongame species. Consult your lo-cal conservation agency or USDA-APHIS-ADC personnel for the legalstatus of chipmunks in your state.

Damage Prevention andControl

Exclusion

Chipmunks should be excluded frombuildings wherever possible. Use hard-ware cloth with 1/4-inch (0.6-cm)mesh, caulking, or other appropriatematerials to close openings where theycould gain entry.

Hardware cloth may also be used toexclude chipmunks from flower beds.Seeds and bulbs can be covered by1/4-inch (0.6-cm) hardware cloth andthe cloth itself should be covered withsoil. The cloth should extend at least 1foot (30 cm) past each margin of the

planting. Exclusion is less expensive inthe long run than trapping, wherehigh populations of chipmunks exist.

Cultural Methods and HabitatModifications

Landscaping features, such as groundcover, trees, and shrubs, should not beplanted in continuous fashion connect-ing wooded areas with the founda-tions of homes. They provide protec-tion for chipmunks that may attemptto gain access into the home. It is alsodifficult to detect chipmunk burrowsthat are adjacent to foundations whenwood piles, debris, or plantings ofground cover provide above-groundprotection.

Place bird feeders at least 15 to 30 feet(5 to 10 m) away from buildings sospilled bird seed does not attract andsupport chipmunks near them.

Repellents

Naphthalene flakes (moth flakes)may repel chipmunks from attics,summer cabins, and storage areaswhen applied liberally (4 to 5 poundsof naphthalene flakes per 2,000 squarefeet [1.0 to 1.2 kg/100 m2]). Use cau-tion, however, in occupied buildings,as the odor may also be objectionable

or irritating to people or pets.

There are currently no federally regis-tered repellents for controlling rodentdamage to seeds, although some stateshave Special Local Needs 24(c) regis-trations for this purpose. Taste repel-lents containing bitrex, thiram, orammonium soaps of higher fatty acidscan be used to protect flower bulbs,seeds, and foliage not intended for hu-man consumption. Multiple applica-tions of repellents are required.

Repellents can be expensive and usu-ally do not provide 100% reduction indamage to horticultural plantings.

Toxicants

There are no toxic baits registered forcontrolling chipmunks. Baits that areused against rats and mice in andaround homes will also kill chipmunksalthough they are not labeled for suchuse and cannot be recommended.Moreover, chipmunks that die fromconsuming a toxic bait inside struc-

tures may create an odor problem forseveral days. Some states have SpecialLocal Needs 24(c) registrations forchipmunk control for site-specific use.

Consult a professional pest controloperator or USDA-APHIS-ADC biolo-gist if chipmunks are numerous orpersistent.

Fumigants

Fumigants are generally ineffectivebecause of the difficulty in locating the

openings to chipmunk burrows andbecause of the complexity of burrows.

Aluminum phosphide is a RestrictedUse Pesticide that is registered inmany states for the control of burrow-ing rodents. It is available in a tabletform, which when dropped into theburrow reacts with the moisture in thesoil and generates toxic phosphine gas.


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Aluminum phosphide, however, can-not be used in, under, or even nearoccupied buildings because there is adanger of the fumigant seeping intobuildings.

Gas cartridges are registered for thecontrol of burrowing rodents and areavailable from garden supply centers,hardware stores, seed catalogs, or the

USDA-APHIS-ADC program. Chip-munk burrows may have to beenlarged to accommodate the com-mercially or federally produced gascartridges. Gas cartridges should notbe used under or around buildings ornear fire hazards since they burn withan open flame and produce a tremen-dous amount of heat. Carbon monox-ide and carbon dioxide gases areproduced while the cartridges burn;thus, the rodents die fromasphyxiation.

Trapping

Trapping is the most practical methodof eliminating chipmunks in mosthome situations. Live-catch wire-meshtraps or common rat snap traps can beused to catch chipmunks. Commonlive-trap models include the Toma-hawk (Nos. 102, 201) and Havahart(Nos. 0745, 1020, 1025) traps. Check theSupplies and Materials section foradditional manufacturers of live-catch

traps.A variety of baits can be used to lurechipmunks into live traps, includingpeanut butter, nutmeats, pumpkin orsunflower seeds, raisins, prune slices,or common breakfast cereal grains.Place the trap along the pathwayswhere chipmunks have been seen fre-quently. The trap should be securelyplaced so there is no movement of thetrap prematurely when the animalenters. Trap movement may prema-turely set off the trap and scare thechipmunk away. A helpful tip is toprebait the trap for 2 to 3 days bywiring the trap doors open. This willcondition the chipmunk to associatethe new metal object in its territorywith the new free food source. Set thetrap after the chipmunk is activelyfeeding on the bait in and around thetrap. Live traps can be purchased fromlocal hardware stores, department

stores, pest control companies, orrented from local animal shelters.

Check traps frequently to removecaptured chipmunks and release anynontarget animals caught in them.Avoid direct contact with trappedchipmunks. Transport and release live-trapped chipmunks several miles fromthe point of capture (in areas where

they will not bother someone else), oreuthanize by placing in a carbon diox-ide chamber.

Common rat snap traps can be used tokill chipmunks if these traps are iso-lated from children, pets, or wildlife.They can be set in the same manner aslive traps but hard baits should be tiedto the trap trigger. Prebait snap trapsby not setting the trap until the animalhas been conditioned to take the baitwithout disturbance for 2 to 3 days.

Small amounts of extra bait may beplaced around the traps to make themmore attractive. Set the snap traps per-pendicular to the chipmunks pathwayor in pairs along travel routes with thetriggers facing away from each other.Set the trigger arm so that the triggeris sensitive and easily sprung.

To avoid killing songbirds in rat snaptraps, it is advisable to place the trapsunder a small box with openings thatallow only chipmunks access to the

baited trap. The box must allowenough clearance so the trap operatesproperly. Conceal snap traps that areset against structures by leaningboards over them. Small amounts ofbait can be placed at the openings asan attractant.

Shooting

Where shooting is legal, use a small-gauge shotgun or a .22-caliber riflewith bird shot or C.B. cap loads. Chip-munks are nervous and alert, so they

make difficult targets. The best time toattempt shooting is on bright sunnydays during the early morning.

Economics of Damageand Control

The majority of chipmunk damage in-volves minimal economic loss (under$200). Homeowners report that chip-

munks are quite destructive when itcomes to their burrowing activitiesaround structures. This damage war-rants an investment in control to pro-tect structural integrity of stairs, patios,and foundations. Their consumptionof seeds, flower bulbs, fruit, and veg-etables is often a nuisance.

AcknowledgmentsWe would like to thank all the USDA-APHIS-ADC wildlife biologists who providedinformation on chipmunks pertinent to theirlocality. Kathleen LeMaster and Dee AnneGillespie provided technical assistance.

Figure 1 from Schwartz and Schwartz (1981).

Figure 2 from Burt and Grossenheider (1976).

For AdditionalInformation

Bennett, G. W., J. M. Owens, and R. M.Corrigan. 1988. Trumans scientific guide topest control operations. Purdue Univ./Edgell Commun. Duluth, Minnesota. 539pp.

Burt, W. H., and R. P. Grossenheider. 1976. Afield guide to the mammals. HoughtonMifflin Co., Boston. 289 pp.

Corrigan, R. M., and D. E. Williams. 1988.Chipmunks. ADC-2 leaflet, Coop. Ext. Serv.,Purdue Univ., West Lafayette, Indiana. incoop. with the US Dept. Agric. 2 pp.

Dudderar, G. 1977. Chipmunks and groundsquirrels. Ext. Bull. E-867, Michigan StateUniv., Lansing, Michigan. 1 p.

Eadie, W. R. 1954. Animal control in field, farm,and forest. The Macmillan Co., New York.257 pp.

Gunderson, H. L., and J. R. Beer. 1953. Themammals of Minnesota. Univ. MinnesotaPress. Minneapolis. 190 pp.

Hoffmeister, D. F., and C. O. Mohr. 1957. Afieldbook of Illinois mammals. Nat. Hist.Surv. Div. Urbana, Illinois. 233 pp.

Marsh, R. E., and W. E. Howard. 1990.Vertebrate pests. Pages 771-831 in A. Mallised., Handbook of pest control. 7th ed.Franzak and Foster Co. Cleveland, Ohio.

Schwartz, C. W., and E. R. Schwartz. 1981. Thewild mammals of Missouri. The Univ.Missouri Press. Columbia. 356 pp.

EditorsScott E. HygnstromRobert M. TimmGary E. Larson


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POCKET GOPHERS


Exclusion

Generally not practical.

Small mesh wire fence may provideprotection for ornamental trees andshrubs or flower beds.

Plastic netting protects seedlings.

Cultural Methods

Damage resistant varieties of alfalfa.

Crop rotation.

Grain buffer strips.

Control of tap-rooted forbs.

Flood irrigation.

Plant naturally resistant varieties ofseedlings.

Repellents

Synthetic predator odors are all ofquestionable benefit.

ToxicantsBaits:

Strychnine alkaloid.

Zinc phosphide.

Chlorophacinone.

Diphacinone.

Fumigants:

Carbon monoxide from engineexhaust.

Others are not considered veryeffective, but some are used:

Aluminum phosphide.Gas cartridges.

Trapping

Various specialized gopher kill traps.

Common spring or pan trap

(sizes No. 0 and No. 1).Shooting

Not practical.

Other

Buried irrigation pipe or electrical cablescan be protected with cylindrical pipehaving an outside diameter of at least2.9 inches (7.4 cm).

Surrounding a buried cable with 6 to 8inches (15 to 20 cm) of coarse gravel(1 inch [2.5 cm] in diameter) mayprovide some protection.





Ronald M. Case

Professor of Wildlife BiologyDepartment of Forestry, Fisheries

and WildlifeUniversity of NebraskaLincoln, Nebraska 68583-0819

Bruce A. Jasch

Research AssistantDepartment of Forestry, Fisheries

and WildlifeUniversity of NebraskaLincoln, Nebraska 68583-0819

Fig. 1. Plains pocket gopher,Geomys bursarius


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B-18

sensory mechanism guiding gophersbackward movements. The tail is alsoimportant in thermoregulation, actingas a radiator.

Pocket gophers are medium-sizedrodents ranging from about 5 to nearly14 inches (13 to 36 cm) long (head and

body). Adult males are larger thanadult females. Their fur is very fine,

soft, and highly variable in color.Colors range from nearly black to pale

brown to almost white. The great vari-ability in size and color of pocketgophers is attributed to their low dis-persal rate and thus limited gene flow,resulting in adaptation to local condi-tions.

Thirty-four species of pocket gophers,represented by five genera, occupy thewestern hemisphere. In the UnitedStates there are 13 species and three

genera. The major features differentiat-ing these genera are the size of theirforefeet, claws, and front surfaces oftheir chisel-like incisors (Fig. 3).

Thomomys have smooth-faced incisorsand small forefeet with small claws.Northern pocket gophers (Thomomystalpoides) are typically from 6 1/2 to 10inches (17 to 25 cm) long. Their fur isvariable in color but is often yellowish

brown with pale underparts. Bottas(or valley) pocket gophers (Thomomys

bottae) are extremely variable in sizeand color. Bottas pocket gophers are 5inches to about 13 1/2 inches (13 to 34cm) long. Their color varies fromalmost white to black.

Geomys have two grooves on eachupper incisor and large forefeet andclaws. Plains pocket gophers (Geomysbursarius) vary in length from almost 71/2 to 14 inches (18 to 36 cm). Theirfur is typically brown but may vary to

black. Desert pocket gophers (Geomysarenarius) are always brown and varyfrom nearly 8 3/4 to 11 inches (22 to 28

cm) long. Texas pocket gophers(Geomys personatus) are also brown andare from slightly larger than 8 3/4 tonearly 13 inches (22 to 34 cm) long.Southeastern pocket gophers (Geomys

pinetis) are of various shades of brown,depending on soil color, and are from9 to 13 1/4 inches (23 to 34 cm) long.

Pappogeomys have a single groove oneach upper incisor and, like Geomys,have large forefeet with large claws.Yellow-faced pocket gophers(Pappogeomys castanops) vary in lengthfrom slightly more than 5 1/2 to justless than 7 1/2 inches (14 to 19 cm).Their fur color varies from pale yellowto dark reddish brown. The under-parts vary from whitish to bright yel-lowish buff. Some hairs on the backand top of the head are dark-tipped.

Range

Pocket gophers are found only in theWestern Hemisphere. They range from

Panama in the south to Alberta in thenorth. With the exception of the south-eastern pocket gopher, they occurthroughout the western two-thirds ofthe United States.

Fig. 3. These three genera of pocket gophers can be differentiated by relative size of forefeet and front surfaces of upper incisors.

Thomomys PappogeomysGeomys

Incisors always exposed

Opening of fur-linedcheek pouch

Fig. 2. Pocket gopher characteristics.

Identification

Pocket gophers (Fig. 1) are fossorial(burrowing) rodents, so named be-cause they have fur-lined pouches out-side of the mouth, one on each side ofthe face (Fig. 2). These pockets, whichare capable of being turned inside out,

are used for carrying food. Pocket go-phers are powerfully built in the fore-quarters and have a short neck; thehead is fairly small and flattened. Theforepaws are large-clawed and the lipsclose behind their large incisors, allmarvelous adaptations to their under-ground existence.

Gophers have small external ears andsmall eyes. As sight and sound areseverely limited, gophers are highlydependent on the sense of touch. The

vibrissae (whiskers) on their face arevery sensitive to touch and assistpocket gophers while traveling aboutin their dark tunnels. The tail issparsely haired and also serves as a


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Fig. 4a. Range of the plains pocket gopher(Geomys bursarius) (dark) and Bottas pocketgopher (Thomomys bottae) (light) in NorthAmerica.

Plains pocket gophers (Geomysbursarius, Fig. 4a) are found in the cen-tral plains from Canada south throughTexas and Louisiana. Bottas (or val-ley) pocket gophers (Thomomys bottae,Fig. 4a) are found in most of the south-ern half of the western United States.

Northern pocket gophers (Thomomystalpoides, Fig. 4b) range throughout

most of the states in the northern halfof the western United States. Yellow-faced pocket gophers (Pappogeomyscastanops, Fig. 4b) occur from Mexico,along the western edge of Texas, east-ern New Mexico, southeastern Colo-rado, southwestern Kansas, and intothe panhandle of Oklahoma.

Southeastern pocket gophers (Geomyspinetis, Fig. 4c) are found in northernand central Florida, southern Georgia,and southeastern Alabama. Southern

pocket gophers (Thomomys umbrinus,Fig. 4c) range primarily in CentralAmerica, but occur in extreme south-western New Mexico and southeasternArizona. Desert pocket gophers(Geomys arenarius) occur only in south-western New Mexico and the extremewestern edge of Texas. Mazamapocket gophers (Thomomys mazama,),mountain pocket gophers (Thomomysmonticola ), and Camas pocket gophers(Thomomys bulbivorus) have more lim-ited distributions in the extreme west-

ern United States.

Habitat

A wide variety of habitats are occu-pied by pocket gophers. They occurfrom low coastal areas to elevations inexcess of 12,000 feet (3,600 m). Pocketgophers similarly are found in a widevariety of soil types and conditions.They reach their greatest densities onfriable, light-textured soils with good

herbage production, especially whenthat vegetation has large, fleshy roots,

bulbs, tubers, or other undergroundstorage structures.

The importance of soil depth and tex-ture to the presence or absence ofgophers is both obvious and cryptic.Shallow soils may be subject to cave-ins and thus will not maintain a tunnel.Tunnels are deeper in very sandy soils

where soil moisture is sufficient tomaintain the integrity of the burrow. Aless visible requirement is that atmo-spheric and exhaled gases must diffusethrough the soil to and from thegophers tunnel. Thus light-textured,porous soils with good drainage allowfor good gas exchange between thetunnel and the atmosphere. Soils that

have a very high clay content or thosethat are continuously wet diffuse gasespoorly and are unsuitable for gophers.

Pocket gophers sometimes occupyfairly rocky habitats, although thosehabitats generally do not have morethan 10% rocks in the top 8 inches (20cm) of soil. Pocket gophers appear to

burrow around rocks greater than 1inch (2.5 cm) in diameter, but smallerrocks are frequently pushed to thesurface.

Soil depth is also important in amelio-rating temperatures. Soils less than 4inches (10 cm) deep probably are toowarm during summers. Shallow tun-nels may also limit the presence ofgophers during cold temperatures,especially if an insulating layer ofsnow is absent.

Typically, only one species of pocketgopher is found in each locality. Soilfactors are important in limiting thedistributions of pocket gophers. The

larger gophers are restricted to sandyand silty soils east of the Rockies.Smaller gophers of the genusThomomys have a broader tolerance tovarious soils.

Food Habits

Pocket gophers feed on plants in threeways: 1) they feed on roots that theyencounter when digging; 2) they maygo to the surface, venturing only a

body length or so from their tunnel

opening to feed on abovegroundvegetation; and 3) they pull vegetationinto their tunnel from below. Pocketgophers eat forbs, grasses, shrubs, andtrees. They are strict herbivores, andany animal material in their dietappears to result from incidentalingestion.

Alfalfa and dandelions are apparentlysome of the most preferred and nutri-

Fig. 4c. Range of the southeastern pocket gopher(Geomys pinetis) (dark) and southern pocketgopher (Thomomys umbrinus) (light) in NorthAmerica.

Fig. 4b. Range of the northern pocket gopher

(Thomomys talpoides) (dark) and yellow-facedpocket gopher (Pappogeomys castanops) (light) inNorth America.


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tious foods for pocket gophers. Gener-ally, Thomomys prefer perennial forbs,

but they will also eat annual plantswith fleshy underground storagestructures. Plains pocket gophers con-sume primarily grasses, especiallythose with rhizomes, but they seem toprefer forbs when they are succulent inspring and summer.

Portions of plants consumed also varyseasonally. Gophers utilize above-ground portions of vegetation mostlyduring the growing season, when thevegetation is green and succulent.Height and density of vegetation atthis time of year may also offer protec-tion from predators, reducing the riskof short surface trips. Year-round,however, roots are the major foodsource. Many trees and shrubs areclipped just above ground level. Thisoccurs principally during winter undersnow cover. Damage may reach ashigh as 10 feet (3 m) above ground.Seedlings also have their roots clipped

by pocket gophers.

General Biology,Reproduction, andBehavior

Just as cheek pouches are used in iden-tification of pocket gophers, their fan-shaped soil mounds are characteristicevidence of their presence. Typically,there is only one gopher per burrowsystem. Obvious exceptions are whenmating occurs and when the female iscaring for her young.

All pocket gophers use their claws andteeth while digging. Geomys, however,are primarily claw diggers, whileThomomys do much more tooth dig-ging, and Pappogeomys are intermedi-ate between the two. Soil, rocks, andother items loosened by this means are

kicked away from the digging areawith the hind feet. Gophers then turnover, making a sort of somersaultwithin the confines of their burrow,and use their forefeet and chest topush the materials out of the burrow.

The incisors of pocket gophers, as in allrodents, grow continuously to repairthe wear and tear on the teeth. On theother hand, gophers must gnaw con-

tinuously to keep their teeth ground toan appropriate length. Gophers exerttremendous pressure with their bite,up to 18,000 pounds per square inch(1,265 kg/cm2).

Burrow systems consist of a main bur-row, generally 4 to 18 inches (10 to 46cm) below and parallel to the groundsurface, with a variable number of lat-

eral burrows off the main one. Theseend at the surface with a soil moundor sometimes only a soil plug. Thereare also deeper branches off the main

burrow that are used as nests and foodcaches. Enlargements along the maintunnel are probably feeding and rest-ing locations. Nest chambers havedried grasses and other grasslikeplants formed into a sphere. The maxi-mum depth of at least some portion ofa burrow may be as great as 5 or 6 feet(1.5 or 1.8 m). The diameter of a bur-row is about 3 inches (7.6 cm) but var-ies with the body size of the gopher.

Burrow systems may be linear orhighly branched. The more linear sys-tems may be those of reproductivemales, since this shape would increasethe likelihood of encountering afemales burrow. The number of soilmounds on the surface of the groundmay be as great as 300 per animal in ayear. Burrows are sometimes quitedynamic, with portions constantly

being sealed off and new areas exca-vated. A single burrow system maycontain up to 200 yards (180 m) of tun-nels. The poorer the habitat, the largerthe burrow system required to providesufficient forage for its occupant.

The rate of mound building is highlyvariable. Estimates include an averageof 1 to 3 per day up to 70 mounds permonth. This activity brings largeamounts of soil to the surface, vari-ously estimated at 2 1/4 tons (2 mt)

per gopher each year up to 46 3/4 tonsper acre (103.9 mt/ha) for a populationof 50 southern pocket gophers.

The tunnel system tells us much aboutits inhabitant. The system is rigorouslydefended against intruders and consti-tutes the home range of the pocketgopher, which may be up to 700square yards (560 m2).

Pocket gophers also tunnel throughsnow, above the ground. Soil from

below ground is pushed into the snowtunnels, but mounds are not built.When the snow melts, the soil casts(tubes) remain on the ground untilthey weather away. Soil casts are left

by both Thomomys and Geomys in areaswhere snow cover is adequate for

burrowing.Pocket gophers do not hibernate. Someobservers believe their activities peakat dawn and dusk, but various studieshave shown them to be active through-out the day, with activity periods in-terspersed with rest. Mound building

by plains pocket gophers increases inspring, frequently declines duringsummer, and increases again in fall. InThomomys, mound building increasesfrom spring through summer into fall.Tunneling underground is a tremen-dously demanding activity estimatedto require 360 to 3,400 times the energyof moving across the surface. Thus,this activity must be of great impor-tance to the pocket gophers survival,either increasing its chance of breedingor finding needed food resources.

Pocket gophers reach sexual maturityin the spring following their birth. Inthe northern part of their range theyhave 1 litter per year. In the southernportion they may have 2 litters per

year. One researcher has suggestedthat Thomomys in irrigated alfalfa inCalifornia may breed throughout theyear.

Litter sizes range from 1 to 10 but typi-cally average 3 to 4. In some southernportions of their range where 2 littersare born each year, litter size is usuallysmaller, averaging about 2. The breed-ing season also varies, but births typi-cally occur from March through June.The gestation period is 18 or 19 days

for the northern pocket gopher, butperiods as long as 51 days for theplains pocket gopher have beenreported. Sex ratios are typically infavor of females, generally rangingfrom 55% to 60% females for Geomys.In Thomomys, the sex ratio is often50:50 but it varies seasonally. Theremay be more males than females inspring and the reverse for summer and


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fall. Pocket gophers have been thoughtto be polygamous (one male matingwith two or more females), but serialmonogamy may be the case. The malecohabits a tunnel system and may helpcare for young before moving on toanother females burrow system. Someresearchers believe both sexes movemainly underground from their own

to other burrows during the breedingseason.

Densities reported for various pocketgophers are highly variable. Densitiesof 16 to 20 per acre (40 to 49/ha) arevery common for Thomomys, but theymay attain densities up to 62 per acre(153/ha). For Geomys, 6 to 8 per acre(20/ha) are representative of high den-sities. Average life span of gophersappears to change inversely withpopulation density. Average longevityfor Thomomys ranges from just over 1year to nearly 3 years. Geomys may liveto an average age of 2 and reach amaximum age in the wild in excess of7 years.

Sharp declines in gopher populationshave been noted on several occasions.Usually some climatic factor is associ-ated with a marked decline. Anexample would be a heavy snowcover, then rapid snowmelt with aconcomitant rise in the water table.

External parasites are often found onpocket gophers. Lice are perhaps themost common, while ticks, fleas, andmites also occur. The contribution ofparasites to gopher mortality isunknown.

Numerous predators eat pocketgophers. Some of the predators pursuethe gopher in its tunnel system (wea-sels, perhaps spotted skunks, and sev-eral snakes including gopher, bull, andrattlesnakes). Badgers are adept at dig-ging out gophers, and a whole host ofpredators prey on gophers when theyare aboveground feeding, dispersing,or while they construct their mounds.Other mammalian predators includecoyotes, domestic dogs, foxes, housecats, striped skunks, and bobcats. Rap-tors that prey on gophers include sev-eral owls, especially great horned and

barn owls, and several hawks.

summer in Nebraska. Theseaboveground movements are a primereason for high mortality in denselypopulated areas.


Several mammals are sometimes con-

fused with pocket gophers because ofvariations in common local terminol-ogy (Fig. 5). In addition, in the south-eastern United States, pocket gophersare called salamanders, (derivedfrom the term sandy mounder), whilethe termgopher refers to a tortoise.Pocket gophers can be distinguishedfrom the other mammals by their tell-tale signs as well as by their appear-ance. Pocket gophers leave soilmounds on the surface of the ground.The mounds are usually fan-shapedand tunnel entrances are plugged,keeping various intruders out of bur-rows.

Damage caused by gophers includesdestruction of underground utilitycables and irrigation pipe, direct con-sumption and smothering of forage byearthen mounds, and change in speciescomposition on rangelands by provid-ing seedbeds (mounds) for invadingannual plants. Gophers damage trees

by stem girdling and clipping, root

pruning, and possibly root exposurecaused by burrowing. Gopher moundsdull and plug sicklebars when harvest-ing hay or alfalfa, and soil brought tothe surface as mounds is more likely toerode. In irrigated areas, gopher tun-nels can channel water runoff, causingloss of surface irrigation water. Gophertunnels in ditch banks and earthendams can weaken these structures,causing water loss by seepage and pip-ing through a bank or the completeloss or washout of a canal bank. Thepresence of gophers also increases thelikelihood of badger activity, whichcan also cause considerable damage.

Legal Status

Pocket gophers are not protected byfederal or state law.

A great diversity of vertebrates hasbeen found in the burrows of pocketgophers. It is especially interesting tonote how gophers react to those ani-mals. Most amphibians and lizards arelargely ignored. Ground squirrels,kangaroo rats, and smaller rodentsgenerally avoid gophers, frequentlyleaving the tunnel system if occupied

by a gopher. Sometimes gophers blockthe exit of these rodents by construct-ing earthen plugs in the burrow sys-tem. When pocket gophers encountersnakes, weasels, or other threats, theytypically react by assuming a threaten-ing posture with the mouth open,vocalizing with panting sounds, andraising the front of the body slightlywith their claws extended forward.This behavior usually chases awayother gophers in the tunnel. If theintruder is a snake, many strikes

bounce off the gophers incisors andclaws. In addition, the gopher may tryto block the intruder with a wall ofsoil.

Pocket gophers are capable of swim-ming. The southern pocket gopher hasthe greatest endurance of three speciesthat were tested in laboratory condi-tions. The plains pocket gopher isintermediate in its endurance betweenthe southern pocket gopher and theyellow-faced pocket gopher. The latter

is a very poor swimmer. The superiorswimming ability of the southernpocket gopher may be an adaptation toits mountain habitat, which frequentlyundergoes flooding during snowmelt.Swimming during flooding may also

be a method of pocket gopherdispersal.

Dispersal of young plains pocketgophers from their natal burrows has

been reported to begin in June in Colo-rado. Young apparently begin to dis-perse when they are only one-third theadult body size. Other indications ofaboveground dispersal of pocketgophers have been reported by inci-dental captures of gophers in driftfences set for snakes. A plains pocketgopher was reported a victim of anautomobile on a highway in Iowa, andplains pocket gophers are reportedfalling into window wells every


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Exclusion

Because of the expense and limitedpracticality, exclusion is of little use.Fencing of highly valued ornamentalshrubs or landscape trees may be justi-

fied. The fence should be buried atleast 18 inches (46 cm). The meshshould be small enough to excludegophers: 1/4-inch or 1/2-inch (6- to13-mm) hardware cloth will suffice.Cylindrical plastic netting placed overthe entire seedling, including the bareroot, reduces damage to newly plantedforest seedlings significantly.

Cultural Methods and HabitatModification

These methods take advantage of

knowledge of the habitat requirementsof pocket gophers or their feeding

behavior to reduce or eliminatedamage.

Crop Varieties. In alfalfa, large tap-rooted plants may be killed or thevigor of the plant greatly reduced bypocket gophers feeding on the roots.Varieties with several large rootsrather than a single taproot suffer lesswhen gophers feed on them. Addition-ally, pocket gophers in alfalfa fields

with fibrous-root systems may havesmaller ranges. This would reducegopher impact on yield.

Crop Rotation.There are many goodreasons for using a crop rotationscheme, not the least of which is mini-mizing problems with pocket gophers.When alfalfa is rotated with graincrops, the resultant habitat is incapableof supporting pocket gophers. Theannual grains do not establish largeunderground storage structures and

thus there is insufficient food forpocket gophers to survive year-round.

Grain Buffer Strips.Planting 50-foot (15-m) buffer strips of grainaround hay fields provides unsuitablehabitat around the fields and can mini-mize immigration of gophers.

Weed Control. Chemical or mechani-cal control of forbs, which frequently

Fig. 5. Mammals that are sometimes called gophers. From top to bottom: Richardson ground squir-rel, thirteen-lined ground squirrel, vole, and mole.

have large underground storage struc-

tures, can be an effective method ofminimizing damage by Thomomys torangelands. It may also be effective inmaking orchards and shelterbelts lesssuitable for pocket gophers. Themethod is less effective for plainspocket gophers as they survive quitenicely on grasses. The warm-seasonprairie grasses have large root-to-stemratios and these food sources areadequate for Geomys.

Flood Irrigation.Irrigating fields by

flooding can greatly reduce habitatsuitability for pocket gophers. Watercan fill a gophers tunnel, thus causingthe occupant to drown or flee to thesurface, making it vulnerable to preda-tion. The soil may be so damp that it

becomes sticky. This will foul thepocket gophers fur and claws. As thesoil becomes saturated with water, thediffusion of gases into and out of the

gophers burrow is inhibited, creating

an inhospitable environment. Theeffectiveness of this method can beenhanced by removing high spots infields that may serve as refuges duringirrigation.

Damage-Resistant Plant

Varieties.Tests of several prove-nances of ponderosa pine showed thatsome have natural resistance to gopherdamage.

Repellents

Some predator odors have been testedas gopher repellents and show somepromise. Commercially available sonicdevises are claimed to repel pocketgophers. There is, however, no scien-tific supporting evidence. The plantsknown as caper spurge, gopher purge,or mole plant (Euphorbia lathyrus) andthe castor-oil plant (Ricinus communis)have been promoted as gopher


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repellents, but there is no evidence oftheir effectiveness. In addition, theseare not recommended as they are bothpoisonous to humans and pets.

Toxicants

Several rodenticides currently arefederally registered and available forpocket gopher control. The most

widely used and evaluated is strych-nine alkaloid (0.25 to 0.5% active ingre-dient) on grain baits. There is someconcern that pocket gophers may con-sume sublethal doses of strychnineand then develop bait shyness. Strych-nine acts very rapidly and gopherssometimes die within an hour afterconsuming a lethal dose. It is regis-tered for use for Geomys spp. andThomomys spp. If the label has direc-tions for use with a burrow buildermachine, then it is a Restricted Use

Pesticide. Zinc phosphide (2%) is lesseffective than strychnine for gophercontrol. Anticoagulants now are avail-able for pocket gopher control. Cur-rently, the only federally registeredproducts are chlorophacinone anddiphacinone.

To poison pocket gophers, the baitmust be placed in their tunnel systems

by hand or by a special machineknown as a burrow builder. Under-ground baiting for pocket gopher con-

trol with strychnine presents minimalhazards to nontarget wildlife, either bydirect consumption of bait or by eatingpoisoned gophers. Poison bait spilledon the surface of the ground may behazardous to ground-feeding birdssuch as mourning doves.

The main drawback to grain baits istheir high susceptibility to decomposi-tion in the damp burrows. A newproduct that contains a grain mixtureplus the anticoagulant, diphacinone, in

a paraffin block not only increases thebaits effective life, but also makes itpossible for more than one gopher to

be killed with the same bait. Once theresident gopher ingests the toxicantand dies, it is typical for a neighboringgopher to take over the tunnel systemand thus to ingest the still-toxic bait.

Hand Baiting.Bait can be placed ina burrow system by hand, using a

special hand-operated bait dispenserprobe, or by making an opening to the

burrow system with a probe. Placingbait in the burrow by hand is moretime-consuming than either of theprobing methods, but there is nodoubt that the bait is delivered to thetunnel system.

The key to efficient and effective use of

these methods is locating the burrowsystem. The main burrow generally isfound 12 to 18 inches (30 to 46 cm)away from the plug on the fan-shapedmounds (Fig. 6). If you use a trowel orshovel to locate the main burrow, dig12 to 18 inches (30 to 46 cm) awayfrom the plug. When the main burrowis located, place a rounded tablespoon(15 ml) of bait in each dire

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