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Home , Columbia spotted frog

EvelynL. Bull,rUSDA Forest Service, Pac f c NorthwestResearch Station, 1401 Geke er Lane,La crande Oreqon 97850

Dietand PreyAvailability of ColumbiaSpotted in Northeastern Oregon

Abstract

Baseline infoflnation on the die! and prcv a\ajlabilirl of Columbia \potted fiogs i\ hcking fron nrort of lhc spccicsrrnge. Diet $as detemined nom Jurrethrough Octobcr 2002 lbr 296 hogs in nonheastemOregon. Number of pre,vi!ems. diet compositioD. and biomass indices $crc comparcd by scx. sire classes.$ater type ( versusrivers). montl. and nudy site. Alailable invertebrateswere dctcrmincd iiom slickr' trupsand dip netiing in ponds amddvers. A total of 1.199prc,"- ilcns were identified $ith an averageof,l.:1 prcr ilcn\ in each sanple lrange = 0 - 28). A wide vadety of prey were idcntiilcd including 33 laDrilie\ l-rom20 ordersof invcrtebrales$,ilh only i ofder! represenring>107. of the composirion: (l l%). /(:1fZ ). and flies(10ti).Onl) l,l9Zoftheprev\lcrcinthclarlals|ages.Femaleiiogsaieabou{60%morebiomassthanalcsoflhc same size. presumablybecause oftheir needto produceeggs. Bionrassof male iiog diet samplesrvere greater in rivers than in ponds with a higher percenlageofstoneflies. *,ater striders.and beetles.! aclilcly fonged all sulnner with the highestbiomass in Scptcmb.r and lhe lowest in July. Ovef the sumnrer.composition of spiders.bcctlcs. and llies decrersed while true bugsand anrs/ \rasps incrcasedir tbe diet. Among studt sites.ants/r'asps were mos! abundanrar |he higher elevations.A higher proportion of inlertebratesoccurred in the larger sizesin the dier comparedwi!h samplcsof availttbleinvetebrates. lntroduction EndangeredSpecies Act. Declincsin thisspecies havcbccn repoftedinYellowstone National Palk Amphibiansmake up an inlponant componentof (Patlaand Peterson 1999). (Hovingh 1993). the aquatichabitats in the BIue Mountains.These and (Reaser2000). The oausesof the speciesserve as good indicatorsofoverall health declinesin.lude loss rnd lrlgmentrrion. offorest and rangelandecosystems because they introductionof prcdators,cattle gruzing,and tlte dependon $,ater for reproduction.and because loss of naturalflood disturbances.Many ol these their permeableskin makesthempafiicularly sen- factorscould also influenceprey availability. sitiveto environmcntaltoxins (Morell J999).We know relativelylittle aboutthe biology o[ therela- Studiesof fbod habitsof the Columbia spot tive healthof their populations,particularly *ith tcd fiog haveshown this speciesto be an oppor- re-qardto disturbances.Increasing incidence and tunistic feeder.taking whateverinveftebrates are intensity of fires and other disturbanceagcnts on, near,or underwater(Turner 1959, Miller 1978, (tloods, drought. introduction of fish, habitat al Whitaker et al. 1983) . teration.livestock -srazing. noxious weed control) Baselineinfonnation on dict and prey avail- in easternOregon may threatenthese and ability of Columbiaspotted frogs is lacking in the integrity of the aquatic habitat. Large-scale nofiheastemOregon and other ponions ofits range. disturbancessuch as fire. may have direct and This frog typically breedsin permanentponds but indirect consequenceson frogs resulting in pre- may spendthe summer.fall, and winter in ponds dation.loss in habitat,or changesin dietand prey or rivers(8u11 and Hayes. 2001. 2002). The fac availability. tors driving the selectionofpond or river habitat This studyprovides basic ecological infornra- arenot fully known, althoughdiet may be one ol' tion on the dietofthe Columbiaspotted frog (Raza severalcontributing factors. The focus ofthis study lLtteirentris).This frog specicsis of interest to was to compareColumbia spottedfrog diet and managersbccause it is classitiedas imperiled by invertebrateavailability betwecnpond and river the Oreg,'nNatural Heritage Program. rs \ensi- habitatsat six studysites. This studywas designed tive by the USDA Forest Scrvice in Region 6, to answerthe tbllowing five questions:1) wcre and as a candidatetbr listing under the Federal frogs consuming invcrtebratesin propofiion to theirabundancet2) did frogs sclcctfor largerprey itemsto maximizetheir energy expenditure for- E-meil:ebulllsf\.fcJ u\ aging;3)did pondor river habitatprovide a greater

North$'estScience. Vol.77, No. rl, 2003 349

O200lh) theNonh"en Scientil'jcA$o.iarion Alll-shcrcsc^rd abundanccof prey or larger prey items for frogs: samplcs.Sampling startedin early Juneafter all 4) $as trog diet the sameat different study arcas; breedingwas completedand cndedin rnid-Octo 5) for what durationof thc summerdid lrogs tbr- ber when nighttimc tcmperaturesdropped below age and did diet di11'er? lreczing.Because activiry level of arthropodsvaries uith timeolday. the ordcr that \luJ) \ires\\cre Methods sampledwas rotatedeach sampling period. StudyArea Frogs were capturedwith dip ncts while I walked along the perimeteror dver edgeat Thi: studlur\ condu.ledat \i\ \iter in luo ur cach of the fbur study sites.Sex and snout-vent tershedsin northeastemOrcgon betweenJune and length (SVL) were recordcdfbr eachfiog, and a October2002 (Table 1). Study arcas were selected diet samplewas obtainedby flushing the ston- basedon the presence()f known breeding sites ach of the lrog with a catheter(2 mm wide, 56 eurdprevious knowledge offiog movements.Each cm long) attachedto a 65-cc sydnge inserted study site hasat leastone breedingpond in lcntic through the mouth and esophagusof the frog habitat(Palustrinc system) (Cowardin et al. l979) (Leglerand Sullivan 1979, Whitakcr et al.I983). and an adjacentlotic habitat (Riverine system) Diet sampleswerc preservedin vialsof 75clretha- widrin,l00 m. exceptthcRainbow site, u'hichlacks nol alcohol and returnedto the lab for identifica- a lolic system.All ponds(lentic) and river habi- tion. I assumedthe entiredict samplewas flushed tats (lotic) are in forestedhabitats and have per- from the frog becauseLegler and Sullivan(1979) manent$,ater in typical years.The breedingponds were confident that they recoveredall the mate range from 60 to 30.000 m'?in size.The e;Lrliest rial in the stomachsof lizards basedon dissec- breedingactivity occurs at the Hohman pond in tion of a few lizards after f'lushingthe stomach; late March and the latestoccurs at Rainbowpond however,no fiogs werekilled to testthis assump- in late April or early May (Table 1). The infor- tion. We attemptedto collect tive diet samples mationonbreeding dates was obained by checking from thc first five frogs capturedin both thc pond the ponds every l-2 days atier ice melted. Tim and river at eachstudy site, but limited the time ing of breedingactivity at thesestudy sites is a searchingfor frogsto 2 hr at eachsite. Food frag- function of elevation.exposure, and temperature mentswere identified to ordcr or family and cat ofthe water source.The pondsat HohmanrrLrely egorizedinto six sizeclasses (l-.1.5. 5-9.5. l0- fieeze,while all otherpond srufaces typically frccze 14.5,l5 19.5.20-21.5,>25 rnm)when enough in Novemberand thaw betweenMarch and May. ol'the inr enebrute u r( presentto estirnate.i,/e. Biomass (mg) was determinedby oven-dry- D et Sample ing cach samplefor 24 hr at 40' C. The largest Diet sampleswere collcctcd every 2 wk fiom tiogs sampleswere dried for,18hr. Because size offrog capturedin pond and river habitatsat thc Gun, largely determinedtlte size and amount of prey Starkey.Tailings, irnd Rainbow study areas.Five the frog could consume,I devised an index to percent standardizefor frog size(biomass divided by SVL of frogs captured lacked any stomach * contents.and thcse fiogs were not included in 100). thc sample.Diet was not determinedin two study The nunber ol prey items, diet composition, sites due to difnculty in locating fiogs firr diet andbiornass indices were compared by ( 1) sex.

TABLE l. Pond sizc and depth. datesof breedimg,elevation, and location of sir study sites usedto monitor Columbia spotted liogs in northeanem Oregon,2002.

Study Area Pund depth t|ll) Dalcs of egg layiDg Elevation(m)

Gun 887 0.8 7 17Apr 02 921 Hohman 100 I 3l N{ar-I 2 Apr 02 935 Starke)_ '1,132 30 N{aFApr 98 1.001 30,000 0.1 8 1'1Apr02 t.188 Tailings 86 26,1 0.6-2 15 25Apr 02 1,380 Ranrbo'\, 28,526 3 ll 2EMa! 02 1,810

350 Bull (2) frog sizeclass (355 mn. 56-70mm. and>70 The two methodsof samplingprovide a mea- mm SVL), (3) watertype (pond versusriver), (,1) sureof the relativeabundance of aerialand aquatic month. and (5) study site. For number of prey invertebrutes, but theyare not dfuecdycompamble. itemsand biomass iodices. t-tests were used for Forinvefiebratescaptured on sticky trapsand dip comparisonsbetween sexes and water types. nets,the numberof jnvertebrates,the number by Analysis of Variance (ANOVA) and a post-hoc invertebratesize class, and the compositionwere Tukey's B pair-wise comparisoutest were used comparedby water type, month (June through to comparc frog sizc classes.months. and study August),and site usingt-tests and ANOVA and a arcas.Chi-squarc Lcsts wcrc usedfor all diet com- post-hocTukey's B pair wisecomparison test. The po.itioneonrprri.onr. lt' thc initialcomlrri:on compositionoforders comprising >5'l,: ofthe total betweensex revealeddifferences, subsequent numberol pre; item. ul. usedfor comparison. compadsonswere done for each sex separately. Becausedata were aggregatedby day, the mean Significancelevel was sel at P = 0.05. tbr multiple samplescollected on individual days was usedas thc variable.The relativeabundance lnvertebrateAva ability (proportion)ofinvertebrates occuning in thc diet and within each trap type was comparedusing lnvefiebrateswere sampled using two methods chi-squaLreanalyses for the ordersthat were rela- (sticky ffap and dip net) at the same2-wk inter- tively common. val that diet sampleswere collected fion June until late August (when wasps startedconsum- Besults ing most of the invertebrateson the sticky traps). This time periodwas selected fbr samplingbecause Numberof Preylterns it coincidedu'ith liog presenceat thesites. Sam- BetweenJuneand October, 296 diet sampJeswere pling occumedbetween the hoursof 0900 and collectedat the 4 studysites tiom i7l femaleand 1800,and the sequencethat the six studysites 125male frogs.A total of 1.299prey items wcrc werc samplcdwils rotatedto reducebias. Place- identified(t =.1.410.23) rangingfiom no iden- mcntofsticky raps anddip ncttingoccuncd whcrc titiable prev to 28 prey items per sample.No sig- frogswould likely be teedingbased on telemetry nificant diffcrcnccs were detectedin number of Iocationsin a previousstndy (Bull andHayes 200I) preyitems by sex.water type. month, or site.Frogs Slicky traps were usedto sampleaerial invcr- >70 mm SVL ate significantly more prey items tcbratcsat thc pond or rivcr at cach sitc. A sticky (x = 5.l prey itens) than frogs 56-70 mm SVL trap consistedof a clear four-sidedplastic cover (x = 3.1iprey items) (P = 0.04). lor planfs that was 2,1cm high and attachedto a piece of white styrofoam floating on the water DietCompos t on surface.Four pieces ofclear plastic sprayed with A wide variety ofprey was found in the diet samplcs Tanglefbotwere four sides attachedon the ofeach with only three ordersrepresenting 2107r of the plant with velcro.These were cover traps collected composition:beetles (21%), ants/wasps (21 7.), every 2 wk, returned to the lab where inverte- and flies ( l0'/o) (Table2). Only l47o of the prey bratesin a 10 by 10 cm squarein the centerof itemsuere in lcr\al.lages. Pre) ilem: \ erepri- eachpiece were identifiedto order(Bemor and marily in the smallcrsizc classes: 407. $ere l- Delong1971), and catcgorized into six size classes. 4.5mm in length,29olcwere 5-9.5 mm, 219rwere Aquatic invertebrateswere sampledwith lbur 10-14.5mm, and 10% > 15mm (Figurel). Com- swcepsof a dip net (35 by 20 cm frameand 2 positionof frog diet by orderofinvertebrates dif- mm mesh) at eachpond or river stretch.Sweeps f'eredsigniticantly by watertype (P < 0.01) (Table wcrc perpendicularto the shore,I n in length on 2) and among frog size classes(P = 0.02), but thesubstrate. ending at theshoreline, and at Ieast not by sex. For those477 prey items that could 10 m fiom previous sweeps.Invertebmtes were be identitied to tirmily, composition of diet by idcntificdto ordcr(Mcritt andCummins 1978). farnily differed significantly by waler typc (P < categorizedinto the same six size cllrsses.and 0.01),by sex(P < 0.01)and among lrog size classes releasedto reduceimpact on invenebratepopu- (P < 0.01).A higherproponion of stoneflies,water lations. striders,and beetlesoccurred in diet samplesin

ColumbiaSpotted Frog Diet 35| 'IAtsLE 2. Number of 1.299 prey items identilied to ord.r Two rcccntly transformcd Columbia spottcd or frmily thar lvere lbund in dict s.rnplcs ofCo frogs were fbund in the stoorachof a temale at in ponds and riv lumbia spottcd lrog! caplurcd Rainbow pond, and a Pacifrc txeefto9(H!"la ragilki) cn in nonhcastcrnOregon,2002. Pref iremscom- prising

352 Bull 100 f-= 1-4.5mm m 5-9,5mm F80 I 10-14.5mm N\\\ 15-19.5mm E : 20-24.5mm 460 |re > 24.5 mm

o 640 .ct a, E a) E20

Dieisample Stickytrap Dip net Sampletype

Figurc L Proporlionofinlcrlebralcs b! sizc classconsumedby liogs andcapturedon sticky trapsand in dip net salnples.

8uo E '[o oo E o 9 q) E20 0 o Eo E10

Gun Starkey Taillngs Rainbow Studysltes

Fieure 2. Pfoportion of in|ertebratesin six orders found in Columbia spotrcdliog diel in lbur nudy sites.Only orders$'irh > 50 prey items afe di\pla!ed.

ColumbiaSpotted Frog Diet 353 - Splders Nl True bugs I Leaf hoppers F40 m Baelles .9 t-l Flies El Ants/waaps o30

(,o t20 o o - 10

July August September Month

Figure L Proportionof in\edebratesin six ordersfound jn Columbia spotlcdfrog dicl in cach of four months.Only orderswjth > 50 pre]' items are displa,vcd.

were larger when comparedb sticky traps (Fig- Discussion ure 1). Higher numbersof all invertebrates(P < Prey items found in diet samplessuggested that 0.0l.)and of dragonflies(P < 0.01).damselflies the Columbia spottedliog is a generalist.con- (P < 0.01),back swinmers (P < 0.0l) diving , suminga widerarietl ofprcl u ithinthe.ize runge waterbeetles (P = 0.03) leeches(P = 0.03),crus , that it can catch and ingest (Table 2). Frog diet (P < maytlies(P < taceans 0.01),and 0.01)oc- con\isledof a higherpercentage ol'lrrger inrer- cuffed in pondsthan in rivers.No significantdif- lehrale\Ihan \\a\ \apluredon stickl trap.or in in ferencesoccurred total number by size class dip nets (Figure l), which suggestsa selection in ponds in rivers.No or sizeclass b), site or sig- forlarger prcy to maximizecaloric return for cap nificantdit'ferences occurred in compositionby ture effofi. It appearedthat male frogs in rivers sitc. were able to obtain more biomassthan males in AvailabiJityof invertebratesby ordercaptured pondsbased on biomassindices, although no dif- in sticky traps and dip netsdiftered significantly ferenceswere detectedin biomassobtained by fiom whatwas firund in thefiog diet(P < 0.01;P femalesamong water types. < 0.01).Size class also dift'eredbetween avail- Findings of this study concur with the great able invertebratesand thosein the diet sample diversity of fbod items lbund in the three other (stickytrap: P < 0.01;dip net:P < 0.01).Invene- quantitativestudies evaluating diet of this frog bratescaptured on sticky traps and dip netsrep species.[n westemMontana, 5 L7prey items iden resentedonly a portion of prey availableto Co- tified in 50 stomachcontents included 357. beetles. Iumbia spottedfi'ogs. By taxonomic group,52clr 2270ants/wasps, l47o spiders.9% flies,5% true and 227r of the frog diet comprisedinvefiebrates bugs,57. butterfliesand ,and <57c in other capturedin sticky trapsand dip net samples.Ter- orders(Miller 1978).In centralOregon, 206 diet restrialinveftebrates (e.9., ants, beetles,larvae of samplesrevealed representatives of 63 families buttedlies and moths) and waspsmade up l77r in 19orders (Whitnker et al. 1983).In Yellowstonc and 87r,ofthe frog diet but werc not detectedwith Parl in Wloming. 70-g0r;of 802 prel itenr. my samplingtechniques. fromlT8 fiogs were spiders,true bugs, beetles,

35,1 Bull TABLE 3. Percentof invertebratesin frog diel samples,on had larger diet samplesthan males of the same sticky traps. and in dip net sanples identified to size,while females(55 mm SVL consumedless ordcr or lamil) thal werelbund in Columbiaspot- prey ted frog diet samplcsor capluredin lrapsin ponds thao males of the samesize. These smaller and rivers in northeasternOregon.2002. Invcrtc ltmales will probably not be reprcductive the bratescomprising <5% of the die!. nicky traps. following year (Licht 1975), so that there may of dip nets are not listed. not havebeen the energyneeded for egg produc- tion. Frog Stickt' Dip Ph)lurn/Cla\vOrder,f amily Diet Trap Nct Ourfindingssuggest that fiogs foragedactively fiom June through Septemberand into October ('nolluskt at the Gun and Rainbow siteswith greaterbiom- Castropoda(snails) Aft hropoda () assindices in Septemberthan in July.It is likely Crustacea(crustaceans) that active foraging occured prior to Junc, al- Amphipodr (scuds) thoughdiet sampleswere not collectedthen. These Arachnida () observationssuggest fiogs weremaxirnizing their Arancac (spidcrs) foraging late in the season.presumably for over- wintering, or for egg production in the case of Ephemeroptera(mayfl iet females.The differencesin composition of diet Larvac by month may well reflect relativeavailability of Odonata(draSonflies invertebratesat different times during the sum- and dansellliet (Figure La ac 6 mer 2). Spidersandleafhoppers were most Hemiptera (!rue bugs) abundantin July on both sticky traps and in diet Corixidae ($'aterboaxnen) 8 samples.Beetles \\,ere most abundantin Junc in Geffidae (water striders) the diet but in July on sticky traps. No|oncclidae(backswinnen) 6 Differencesin diet amongstudy sites were ob Holnoprera(leaf hoppers) l6 servedin this study (Figure 2) and Whitaker et Coleoptera(beetles) al. ( 1983).They suggestedthat pastmanagement Aduhs I Larvae 3 practices,particularly livestockgrazing, contrib- Carabidae(ground beetles) uted to dift'erencesin diet. The Starkeysite was Trichoptera(caddisfl iet the only one with livestock grazing in our study, 1 andthis site had a moreeren distribulion among Diptcra (tlics) the primary orders used for prey than the other 11 studysites. An obviousdifference among the study Hynenoplera (ants.bees. wasps) t siteswas the high percentagesof wasps at Tail- Formicidae(ants) t2 ings and Rainbou the two siteswith the highest E elevatiors.Either thesesites had a higher Total t.299 38.589 1.521 density ofwasps thanthe other sitesor a lower densityof otherprey. Wasps were able to escapefrom sticky flies. and ants/wasps(Tumer 1959).In , traps,so that relativeavailability ofthis prey item 8,1%of prey iternswere <9.5 mm in lengthin can not be detemined amongthc sites. comparisonto 69cloin this study.Tumer (1959) The resultsof samplingavailable inveftebrates rugge.teLllhc pcrk of foragingin W;omingurs \uggestthat ponds pror ided more aqurtic inver- July and August with less foraging in June and tebrates,but abundalceof aerialinvertebrates was SeptemberIn contrast.the greatestbiornass in- fairly evenbetween ponds and rivers.In spite of dicesoccurred in Septemberin this study.Some this presumablygreater prey basein ponds,diet of these difterences in prey size and temporal samplesof males had greaterbiomass on nvers. foraging behavior may be due to the higher el- which may be a primary reasonfrogs inhabited evation,colder climate, and smaller fiogs fbund rivers over ponds (Bull and Hayes 2001). Addi- inYellowstonePark than in northeastemOregon. tional facton that could enter into the selection Femalelrogs appeiuedto maximize the amount of habitatinclude predationand water tempera- of prey they could ingestbecause of the needto ture,as it relatesto metabolicmte. Research com- produce eggs annually.Females >55 mm SVL paring kinds and rates of and water

ColumbiaSpotted Frog Diet 355 temperaturesbetween ponds and riverswould be fiog diet samples,and Kent Coe and Bdttany intbrmativcand may shedsome light on the de- McKinnon identified insectson sticky traps.Jay clinesofthis specieswithin ponionsofits range. Shepherdconducted the statisticalanalyses. Roy Beckwith,Jane Hayes, Jim Mclver, and David Acknowledgements Pilliod reviewedan earlierdrati ofthe manuscript. Abe Clark andJanetHohmann assisted with field Fundingwas provided by theU.S. FishandWildlife work. Roy Beckwith identilied arthropodsin the Scrvicc and Pacific NorthwestResearch Station.

LiteratureCited Licht, L. E. 1975. Comparativelife history featufes of the wcncm spotlcd frog. R.rr.r /,"erior.J.lioln low and Borror, D. J., and D. \1. Delong. 1971.An Introduction to high-elelation populations.Canadian Joufnal of Zo- the Srud,,-ol lnsecrs.Third edirion.Holr. Rirehaftand olog_v53:125,t 1257. Winslon. \er York. Medu, R. W. and K. W. Cu'nnins (editofs). 1978.An In- Bull. E. L...tnd !1. P Hayes.2001. Poslbreeding season troduction to thc Aqualic lnsec6 ol Norlh America. movements oi Colunbia spotted fiogs (Rdfld Kendall/Hunt Publishing Company. /l/€ircr/ri.r) in nonheastemOregon. Wesrem Norrh Mijler. J. D. 1978.ObservalioNon thediets ofRdrdtr"/i,r!rr. AmcrlcanNatLrralin 6l il19 123. pipien\. and Bufu boreu iiom wcstcm Mon Bull. E. L.. and M. P Hayes.2001. Over\l'interingofColun- una. Northwest Science52:243 2,19. bia spottedfrogs ln notheastern Oregor. Northwest N{orell.V I 999.Are pathogensfelline frogs?Science 284:728 ScieDce76:1.11-147. 7lL Patla. D. A., and C. R. Peterson.1999. Are amphibiansde Cowardin. L. N1..V Carrer, F C. Goler, and E. T. LaRoe. clining in Yellownonc National Parkl Ycllo$stone 1979.Classilicalion oI lretlands and deepwaGrhabi Science1999:2-l L mN oi lhe United SuGs. United Slales Departmenl Reascr.J. K. 2000. Demographic analysisof the Columbia of the lnlerior. Fish and Wildlile Service. Oilice of spotted frog (Runu luteitentrit). casc study in spa Bi,toAi.ul s

-156 Bull