geophagy in bears

8/13/2019 Geophagy in Bears

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GEOPHAGYBYYELLOWSTONE RIZZLY EARSDAVID . MATTSON',U.S. Gelogical Survey Forest and Rangeland Ecosystem Science Center and Department of Fish and WildlifeResources,University f Idaho,Moscow, D83844, USAGERALDI.GREEN, Coeur d'Alene TribeFish, Water and WildlifeOffice, P.O.Box 408, Plummer, ID83851, USA, email:[email protected] SWALLEY,U.S. Gelogical Survey Interagency GrizzlyBear Study Team, ForestrySciences Lab,Montana State University,Bozeman,MT 9717, USAAbstract: Wedocumented12 sites in the Yellowstoneecosystemwheregrizzlybears(Ursusarctoshorribilis)hadpurposefullyconsumedsoil (anactivityknownasgeophagy).Wealso documented oil in numerous rizzlybear eces. Geophagyprimarily ccurred t sites barren f vegetationwheresurficial eologyhadbeen modifiedbygeothermal ctivity.Therewas no evidenceofungulateuse at most sites. Purposefulonsumptionf soilbybearspeaked irst romMarch oMayandagain romAugust oOctober,ynchronous ithpeaks nconsumptionfungulatemeatandmushrooms.Geophageoussoils weredistinguishedromungulatemineral icks andsoils ingeneralby exceptionallyhighconcentrationsf potassium K)andhighconcentrationsof magnesium Mg)andsulphurS). Our esultsdo notsupporthehypotheseshatbearswereconsuming oil todetoxifysecondaryompoundsngrazedfoliage,as postulated orprimates,or to supplementdietarysodium,as knownforungulates.Ourresultssuggest thatgrizzlybearscould havebeenconsuming oil as an anti-diarrheal.

Ursus 11:109-116

Key words: geophagy,grizzlybear,potassium, odium,sulphur,Ursusarctoshorribilis,Yellowstone

Geophagyandthe use of mineral icks havebeenwell-studied and widely documented among primates andungulates,respectively.Among ungulates, he most con-sistentprimary ffect seems to be supplementingdietarysodium (Na; Jones and Hanson 1985, Tracy andMcNaughton1995). Among primates,anthropologistsandprimatologistsspeculatethatgeophagycan supple-mentdietaryminerals, ncluding ron (Fe), copper(Cu),potassium, alcium(Ca),zinc(Zn),andmanganese Mn);produceanti-diarrhealffects;and counter he effects ofdietary toxins and gastrointestinalparasites(Lovelandet al. 1989, Johns andDuquette1991, Reid 1992). Pri-mate biologists emphasizedthe role that clay mineralsmay playin detoxifyingsecondarycompounds rom foli-ageconsumedbymonkeys Callicebus pp.,Macacaspp.,Saguinusspp.)andgreatapes (HeymannandHartmann1991;Mahaneyet al. 1995a,b, 1996;Muller et al. 1997).

Geophagy amongbears(Ursidae)has been notedonlyrarelyandanecdotally Chatelain1950,JonesandHanson1985). Even so, given their simple digestive tract andomnivorousdiet, it would notbe surprisingf bearscon-sumedsoil largely or the samereasonsasprimates.Manybeardiets include forbs thatcontainpotentiallydeleteri-ous compoundssuch as solublephenolicsandalkaloids(e.g., fireweed [Epilobiumangustifolium]and horsetail[Equisetumarvense]; Kingsbury 1964, Robbins et al.1991). Conversely, heprevalenceof meat nmanybears'diets (a rich source of Na) and markeddissimilaritiesbetween thegastrointestinalractsof ungulatesandursidssuggestthatbearsshould nothave Na deficiencies as do

elk (Cervus elpahus) and bison (Bos bison). Further-more, the dramaticphysiological transitionsassociatedwithhibernationmposeuniquedemandson bearphysi-ology thatmightbe alleviated in unanticipatedways bythe consumptionof soil.Weobserved severalinstances of geophagyby grizzlybears in the Yellowstone ecosystem beginningin 1986as well as numerousoccurrencesof soil in their feces.We speculatethatgeophagy by bearsmay play a role inmaintaining physiological homeostasis and may high-light physiological stressors not previously recognizedfor bears. Given our imitedobservationsof overtgeoph-agy, ourintenthere is to refineresearchhypotheses. Wehope to stimulatefurther nquiryinto geophagy amongbears in this and otherpopulations.We used informationobtainedduringthis study andother publishedinformationon the mineralcontent ofsoils atungulatemineral icks andsoils elsewherein ourstudyarea o test thefollowinghypotheses Ha):(1) min-eralcontentof soils consumedbybearsdiffered romthatof samplesrepresentative f YellowstoneNationalPark(YNP) atlarge;(2) mineralcontentof soils consumedbybearsdifferedfrom that of mineral licks used by ungu-lates in theRockyMountains; 3) soil was positively as-sociated with excavated foods (i.e., roots, rodents,andants [primarilyCamponotus pp. andFormica spp.]) inbearfeces; (4) soil waspositivelyassociatedwithfoliagein feces; and(5) the consumptionof soil coincidedwiththe temporalconsumptionof foliage, controllingfor theeffects of consumingexcavatedfoods.

1Present ddress:USGSForestandRangelandEcosystemScienceCenter,ColoradoPlateauFieldStation,P.O.Box 5614, NorthernArizonaUniversity,Flagstaff,AZ86011-5614,USA, email:[email protected]


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110 Ursus 11:1999STUDYAREAANDMETHODS

Ourstudyareawas theapproximate 3,000-km2 angeof Yellowstone'sgrizzlybearpopulation, ncludingpartsof Wyoming,Montana,and Idaho. We collected fecesthroughouthis range. Geophagysites were foundonlyin YNP, which comprised


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GRIZZLYEARGEOPHAGYMattson et al. 11112- a10- a8- a6- ab ab4 -I b

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Fig.1. Soil inthe feces of Yellowstone grizzlybears bymonth(a)as meanpercentof relativescat volume controllingfor theeffects of year, 1982-92, (b) as relative total volume of soildefecated forthe same period,and(c)as mean(SE)mlvolumeper scat controlling for the effects of other diet items in thesame feces, 1989-92. The black bars in (a) and (b) areestimates when all months were included in the analysis;stippled bars includeonly April-September. Barslabeled bythe same letter do not differ(a = 0.1).

(Fig. lb). The volume of soil in feces was associatedwith month (partial R2 = 0.02) and the volume of allother diet items (Z partial R2s = 0.270; F = 58.07; 16,1199 df; P < 0.0001), but not year (P = 0.469, partial R2= 0.001). Partial relationships were positive with ants,

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Mar Apr May Jun Jul Aug Sep OctMonthFig.2. Percentfrequencyoffeeding activities byradiomarkedgrizzly bears in the Yellowstone ecosystem, 1986-92,excluding locations where no sign of feeding activity wasfoundfor(a)activities involvingthe excavation of foods froma soil matrix, (b) grazing, and (c) feeding activitiesconsistently associated with diarrhetic eces.

mushrooms, odents,ungulates,androots(P coefficients= 0.55, 0.54, 0.43, 0.36, and0.26, respectively)andnega-tive with foliage and whitebarkpine seeds (-0.12 and -0.20, respectively). Controlling or the directeffects ofintermixeddiet items, what could be construed as pur-

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112 Ursus 11:1999poseful soil ingestionpeaked duringMarch-Maywith asecondarypeak duringAugust-October(Fig. Ic).FeedingActivityWe documented eeding activityat 759 of 1,280 loca-tions of radiomarked earsvisitedby researchersduring1986-92. Consideringonly sites with feeding sign, therelativefrequencyof differenttypes of activity variedconsiderablyamongmonths. Activities involvingexca-vation of foods from a soil matrixpeaked duringApril(55%), then declined thereafter to a minimum duringOctober (25%; G = 20.0; 6 df; P = 0.003; excludingMarchbecauseof small samplesizes;Fig. 2a). Thisde-cline was associated with declining relative use of ro-dents anddespiteincreasingrelative use of roots. Peakuse of anthillsoccurredduringJuly(13%). Relative fre-quency of grazing peaked from April-July (32-47%);grazing of graminoidspeaked during April-May (29-39%);andgrazingof forbspeakedduringJune-July 18-22%;G= 76.4; 6 df;P < 0.001; Fig. 2b). The frequencywith which bears consumedungulatemeat was highestduringMarch-April(25-67%) and, with use of mush-rooms, peaked again during September-October(10-12%;G = 21.3; 6 df; P = 0.002; Fig. 2c).GeophagySitesWe documented12 geophagysites. These were siteswheregrizzlybearshadpurposefully onsumedsoil with-out any apparentopportunityto ingest known foods.Consumptionof soil was consistentlyindicatedby deepexcavations, grizzly bear claw marks,bear tracks,andevidenceat some sites thatbears ay on theirstomachsattheedge of excavations. We foundtraditionalbear trailsat 4 sites. Individual xcavations n= 21) averaged189.6dm3 (SD = 239.7, range 3.5-795); total excavatedvol-ume per site (n = 11) averaged362.1 dm3(SD = 323.8,range6.2-1,011). Six of the 11sites wherebearactivity

was documented n detail had 1excavation,3 sites had 2excavations,2 sites had 3 excavations,and 1 site had 4excavations. All but 1 of the sites were associatedwithgeothermally induced hydrothermalacid alteration ofsurficialdeposits(U.S. GeologicalSurvey1972);8 siteswere characterized s unvegetatedsinter.Mostgrizzlybear use of geophagysites occurreddur-ing the spring. Based on investigationsof the 1,280 ra-diotelemetryrelocations,3 sites were used in April, 6sites were used in May, 1 site was used in July,and 2sites were used in August. Ungulate use (exclusivelyelk) was observedonly at the sites used by bears in Au-gust. One of these sites was clearly a mineral lick (wedid not obtain a soil sample). Duringourmonitoringof2 geophagy sites on the northernungulatewinterrangein YNP, we observedrecent (1-7 day-old) excavationsinvolving 12 bears on 10 of 36 visits. One instance ofuse occurred n the first 2 weeks of April, 8 instancesoccurredin the last 2 weeks of April, 2 instances oc-curred n the first 2 weeks of May, and 1 instanceoc-curred n the last 2 weeks of May.

GeophagySoilsSoils at all but1of thegeophagyexcavations themin-eral lick) smelled sulphurous. Where tasted (3 sites),they also were salty. At 6 sites, but not closely associ-atedwith theexcavations, lammablenativesulphurwasconcentrated n the surfaceby geothermalactivity.The mineralcontentof soils from geophagy excava-tions (n = 3), of soils representative f differenthabitattypes in YNP (n = 66), andof soils fromungulatemin-eral licks (n = 61) differedglobally (Wilks' lambda=0.093; 8, 248 df; P < 0.0001) and pair-wisefrom eachother(P < 0.0001 for all comparisons;Table 1). Mostdifferencesamongminerals or the 3 soil types were as-sociated with the first canonicalvariable(83% of totalvariation).Standardizedanonicalcoefficientsof K, Ca,Mg, andNa for this variablewere 1.58, 0.43, -0.19, and-0.95, respectively. When ordinatedby the first 2 ca-

Table . Concentrationf mineralspg/g)nsoilsfrom rizzly eargeophagy itesinYellowstone ational arkYNP; =3), romungulatemineralick ites intheRockyMountainsn=61;Jones and Hanson1985), nd rom oils representativefdifferenthabitatypesinYNPn=66;Trettin985).

RepresentativeitesGeophagyites Mineralicksites inYNPMineral x SD x SD x SDK 397.000 289.000 3.10 4.10 36.30 30.60Mg 49.700 36.900 13.50 36.20 13.90 13.00Na 68.700 41.300 34.90 57.70 1.34 2.38Ca 34.700 23.000 20.40 38.50 211.00 207.00S 0.900 0.350 0.84 0.21Fe 320.000 255.000Mn 4.000 1.900Cu 10.000 6.940P 0.027 0.015Za 1.950 1.130


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GRIZZLYEARGEOPHAGY * Mattsonet al. 113

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114 Ursus 11:1999grizzlybeargeophagysites. Theonlycoincidentelk andbearactivityoccurredat thefew sites usedby bears dur-ing August. Assumingthat elk in YNP use licks prima-rily to supplementdietaryNa (Jonesand Hanson 1985,Tracyand McNaughton1995), it is not surprising hatgrizzly bears would be ingestingdifferenttypes of soilfor different easons. It is very unlikelythatgrizzlybearsin the YellowstoneecosystemexperienceaNadeficiencygiven the largeamountsof meattheyconsume from her-bivores(Mattson1997b)and the high Na content of thisfood (Robbins1983).

Geophageoussoils differedmost strikinglyfrom un-gulate icks and soils representative f YNP by very highK contentand to a lesser extentby high S andMg con-tent. The implicationsof this result in terms of bothcauses andeffects arenot clear. However,it is possiblethat the highconcentration f K andMg in geophageoussoils were nutritionallybeneficial and that the high Scontentwas therapeutic.AdditionalHypotheses

Hibernatinggrizzly bears could incur K deficiencies(hypokalemia). Potassiumundergoesconsiderablecon-centration n the bladderduringhibernation about3.5timesnormal evels;LevinskyandBerliner1959;Brownet al. 1968, 1971). At the same time, urinevolume re-mainsrelativelyconstant(Nelson et al. 1975), althoughdiminishedrom he volumefound nactiveanimals e.g.,Levinsky and Berliner 1959). Hibernationengendersclassic conditionsfor the developmentof hypokalemia:decreaseddietary ntake of K, intestinalobstruction,andrenal excretion of K (or concentration n the bladder;Blood et al. 1979). Although evels of K in blood serumshow relativelylittle variationbetweenhibernatingandactivebears(Nelson et al. 1973), measuresof plasmaorserumK do notreliably ndicatethe statusof the body'sK pool (Blood et al. 1979).If bears emergingfrom hibernationexperienceda Kdeficiency,theymaynot havebeeneasily able to remedytheircondition.In normal ituations,herbivores anboostK intakeby consumingrapidlygrowingvegetalmaterialthat s typicallyrich n K(Robbins1983). However,suchfoods are not readily availableto bears in the Yellow-stoneecosystemuntillateApril. Ourresultssuggestthatgeophagyby grizzlybearspeaksin MarchandApril. IfbearsareK-deficient, his conditionmaybe exacerbatedbydiarrhearomconsumingcarrion cf.Newberne1970).If grizzlybearsduringourstudywerenot K-deficient,theyriskeddamaginglyhigh levels of K (hyperkalemia)by geophagy. This risk would have been off-set some-whatby therelativelyhighlevels of Mg in geophageoussoils (Mg can serve as an antidoteto high levels of K;

NationalAcademyof Sciences [NAS] SubcommitteeonMineralToxicity in Animals 1980, Jones and Hanson1985). However,such a risk is corroborated y recordsin themedical iterature f humanpractitioners f geoph-agy experiencing yperkalemiay ingesting oil with con-centrationsof K comparable o those of soils consumedby Yellowstonegrizzlybears(Gelfandet al. 1975).Theconsumptionof elementalS mayhave had benefi-cial effects, especially duringor soon afterthe transitionfrom hibernation o active metabolism. Sulphurcan actas a parasiticideand fungicide (NAS SubcommitteeonMineralToxicityin Animals 1980), andcan also actas abacteriostatic y alteringhepHof intestinal luids(Bloodet al. 1979). Sulphatesof Na andMg togethercan fur-ther stimulatemotility of the small intestine (Howard1986), which could be very beneficial after winter dor-mancyof the digestivetract.

Geophagyalso could restore beneficial microflora othe intestinesof bears after winterdormancy(T. Beck,ColoradoDivision of Wildlife,Denver,Colorado,USA,personalcommunication,1998). There is evidencethatconsiderabledigestionof fiber can occurin the colon ofmonogastricanimalssuch as swine due to fermentationby anaerobicbacteria Argenzioand Stevens 1984, Low1985). If thesetypesof intestinalbacteriado not survivehibernation n bears, an innoculummight be obtainedfrom soil. This would explain the primaryspring,butnot the secondary ate-seasonpeakin soil consumption.It would also not fit the apparent elective orientationofbearsin our studytowardhomogeneoussites character-ized by exceptionallyhigh levels of K, S, andMg.

RECOMMENDATIONSOurresultscannotconclusivelydemonstratehe causesor consequencesof geophagy to Yellowstone'sgrizzlybears. However,they are a basis for recommendingad-ditionalresearch hatmay provideadditional nsights.1. Analysisof soils fromgeophagysites for claymineralssuch as kaolinite,bentonite,or halloysitewould furtherelucidatewhetherbearsconsumedthis soil for its anti-diarrheal roperties.2. Soil fromgeophagysites couldbe fed to captivebearsexperiencingexperimentally-induced iarrheato directlytest for anti-diarrhealffects.3. Furthernsight into the distributionand abundanceof K in grizzlybearsduringandshortlyafterhibernation ould providea basis for testingthehypothesisthatgrizzlybearsareK-deficientuponden emergence.4. Additional nformationon the year-rounddynamicsof populationsof parasitesandbacteria n the


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GRIZZLYEARGEOPHAGY Mattson et al. 115gastrointestinalract of wild bears could provideadditional nsight into stressors thatmightbealleviatedby the administration f parasiticidesandbacteriostaticsor,conversely,the potentialforaugmentationof beneficialmicorfloraby ingestionof soil.5. The effects of geophagoussoils as parasiticidesandbacteriostatics ould be testedby administeringthem to captivebearsexperiencingexperimentally-inducedlevels of parasitesor bacteria.Our results suggest that the purposefulconsumptionof soil by Yellowstonegrizzly bearsmay play a role intheir maintenance of physiological homeostasis, espe-

cially duringspring. Sites wheregrizzlybearstradition-ally consume soil may therefore warrant specialprotection,not only to ensure thatgrizzlybearshave ac-cess to these locations,but also to minimize thepotentialfor undesirableencountersbetweenhumans and bears.

ACKNOWLEDGMENTSWethank he U.S. Department f theInteriorNationalPark Service and the USGS Biological ResourcesDivi-sion, Forest and RangelandEcosystem Science Centerfor funding this work. Most data collection was con-ducted underthe supervisionof R. Knight. We appreci-atetheunstinting ield work of themanytechnicianswho

helped collect data, especially that of D. Reinhart,J.Henry, and E. Shannahan. Finally, we appreciatethethoughtfulreviews by C. Robbins,J. Cares, T. Beck,and J. Keay.

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