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Oale E. Toweill' ano Roben G. Anthony OregonCooperat ve W ldlifeResearch llnil Departmentof Flsheriesand W ldlle OregonState Universty, Corvals, 97331

AnnualDiet of Bobcatsin Oregon'sCascade Range

Abstract

Becauselittle informarion existson the role of the (-FeIsrz/zs) as a predator in coniferousforesl ecosyslems,rhis srudl wasinitiated to determinethe annual diet ofbobcats in the coniferousfor€st of 0regon's CascadeRange. Diet wasderernined from analysiso{ 494 scats.Dominant pr€} sp€ciesidentified w€re sno{shoe hare\Lepus anericanusl,biackraileddeer (Odo.o;le&r [en;ozzs), and nountain (Aplodontia rufa); renains ofrhese speciesoccurred in 30 percent,22 percenl,and l2 percent of scal! eramined, resp€ctively.A variety of c.icelid and sciurid rodents,birds, insectivor€s,and reptiles rere also identified. The greatestdiversity in the seasonaldiet o{ bobcat occurred during spring, {hil€ the least diversity occurred during winter. Mean prey size taken by bobcarsin the spring (426 g) was approainately half durins winter (827 g). Diets of were nost dissinilar be|{een winter and spring. The vsriety of prey taken seasonatlyby bobcatsand the wide range in prey size indicate the potential for comp€tiiion with othe. predators.Kno{ledge of the seasonalvariation in rh€ bobcatdiet should allow wildlife managersto more effectively nanage both bobcats and their potenlial prey specres. lntroduction Vegetation was typical of the Western (?szgo Little informationis availableconcerning bob- Hemlock heterophylla\ Zone as de- cat food habitatsin coniferousforests of the scribed by Franklin and Dyrness (1973). Logging, PacificNorthwest. Several authors reported on reforestation projects, and forest fires have smallsamples from the CoastRange of western resulted in a dominance of Dou glas- (Pseuclo- Oregon(Schwartz and Mitchell 1945,Sweeney tsuga menziesii) with smaller, isolated stands of 1978,Witmer and deCalestra1986); only Nuss- western red cedar (\. Grand lir baumand Maser(1975) reported bobcat diet in (Abies grand,is),P acific silver fir (), the CascadeRange, This paper reportson the western yew (l"arus 6rez'ilolid), and western white annualand seasonaldiet of bobcatsfrom the cen- (Pinus monticola) occurred commonly. tral CascadeRange of western0regon. Understories were dominated by creambrush oceanspray (Holodiscus discolor) on dry sites, StudyArea Pacific rhododendrot (Rhododend,ron macro This studywas conducted in 0regon'sCascade phyllum) and Cascade hollygrape (Berberis ner- ,within the Willamette National ooia) on intermediate sites, and sword fern Forestapproximately 55 km eastof Eugene,Lane (Polystichum munitum) and Oregon oxalis (Or- County,Oregon (43',55'N; t22',30'W). Ter- alis oregana) onmesic sites (Franklin and Dyrness rain wasabruptly dissected by drainagesof the r973). North Fork of the Middle Fork . Elevationsrange from about500 m to 1,500m. Methods Climate was typical of the Western Cascade Scatswere collected on thestudy area from 15 maritimearea vith mild, wet wintersand warm, Octoberl9B2 through 30 June1984. All roads dry surnmers.Precipitation occurredabout 160 on the280 km' studyarea were cleared of scats daysper year and averagedabout 150cm annual- prior to initiation of daily collectionsso that ly. Meanannual snowfall averaged about 163cm; only freshmaterial was collected. Each scat vas the latestdate with 150cm of snov usuallyoc, labeledand air dried prior to separationand curred in late March (Lahey 1979).Annual identificationof prey remains.Prey items rn some lemperatureextremes ranged from lB to 3BoC. of the scatswere separated from other undigested rPresent address: Fish and Game,109 Vesr 4-1$ Sireet, residuesas collected,but boneswere separated Boise,83714. fiom mostscats using an B percent(2M) solution

NorthwestScience, Vol. 62, No. 3, I98B 99 of NaOH to digestthe associatedcongromerate occurringin 22 percentof scatsexamined (Table (Greenet aL 1986).Samples of hair wereremoved l). remainsoccurred in 27 percentof fall from scats prior to NaOH digestion for com- and3l percentofwinter scats, and were the most parisonwith hair keys(Mayer 1952, Stains 1958, frequentlyidentified prey irem during December Adorjan and Kolenosky1969) to aid in prey and January,when they occurred in 46 percent speciesidentificarions. Bones in the scatswere of bobcatscats. BIack-tailed deer were the sec- identifiedby comparisonwith skeleralmaterials ond mostabundant prey in the bobcatdiet dur- in the vertebratemuseum of the Departmentof ing February,March, April, and May (Tablel). Fisheriesand Wildlife, OregonState University. Remainsof fawnswere identified from a single Eachscat was subjected to a three-partiden- bobcatscat collected in May,from 6 scats(B%) (lB%) tificationprocedure. Each scat was identified to in June,8 from July, and I (2%) from August. speciesin both the field and the laborarorybas, Fawnsaccounted for ll, 55, 6, and 17 percent ed on coloi, texture, odor, and (in the field) of all deerremains identified from bob- associatedtracks and scrapes. A portionof each cat scatscollected in May,June, July, and August, scat wassubjected to thinJayer chromatography respectively.In July, black-taileddeer rernains (fawns for identificationof bile acid residuespresent and adults)were the mostfrequently iden- tified food item. (Majoret ol. 1980,Johnson el al I9Bl, Johnson Remainsof calf (Ceroas et aL 1984).Chromatography was used to derive e/op&.zs)were identified in four bobcatscats from final identification where other characteristics June and July. werenot definitive. Mountain beaverwere the third-rankingitem in bobcatdiets, and occurredin greatestfrequen- Similarity indices(SI) betweenseasonal diets cy during spring (16%) and summer (17%) were calculatedaccording to Horn (1966);using months.Cricetid rodents of 9 species(Table l) the index,values could range between zero (no occurredin 23 percentof the scats,varying from food items in commonbetween seasons) and I 9 percent in winter to 37 percent (identicaldiets betweenseasons). in spring. Six speciesof sciuridrodents (Table l) comprisedl7 Meanprey size was calculated seasonally for percentof the bobcat diet. Squirrelswere eaten all speciesidentified from bobcat scats and by bobcatsmost frequently in the fall (28%)and weighted by frequency of occurrence.This least frequentlyin the sumrner(ll%). Insec- calculationprovided a slight over-estimateof tivoreswere found in l7 percentof bobcatscats meanprey size since several specimens of small duringspring months, but did not occurrn scats prey of the samespecies in a singiescat were from other seasons(Table l). The mostfrequently recordedas one occurrence,as was a single identified insecrivore,the coastmole (Scapozzs specimenof larger"ize. Ungulate remains werp orarias),occurred in 13 (7%) springscats. excludedfrom thesecalculations sincemany may Remainsof birdsoccurred in 4? (10%)scats. havebeen eatenas carrion.Weights of adult Most rryerepasserines, but only I slate,colored mammalswere (l98l) takenfrom Maserer al and jrnco (lunco hyemalis) and ll ruffed grouse fromweights recorded for museum specimensal (Bonasaumbellusl could be positivelyidentified. OregonState University.Mammal nomenclature Eggshellfragments occurred in 5 scats.Reptile follows et (1982); Jones al, plant nomenclature remainsoccurred in 9 percentof springscats. follows Garrison et al. (1976). Like insectivores,reptiles occurred in the bob- cat diet only during spring(Table l). Results Masticatedgreen grass was found in 55 (l I %) Four hundred ninety-fourbobcat scats were of the scats,and somescats consisted solely of analyzed (Table l). hares (Lepus grass.On two occasions,freshly passed scats that americanus),black-tailed deer (Odocoileushe- consistedsolely of masticatedgrass and entwined mionus),al;d (lplod.ontia rufa) tapewormswere found. Blackberries(Rz6as sp.), werethe food itemsmost commonly identified. huckleberries (I/accinium sp.), Cascadeholly- Haresmade up the largestportion of the diet grape(Berberis neraosa), and manzanita(Arcto throughoutthe yearand occurredin ) 33 per- staphylossp.) were identified in 33 (7%) scats. cent of scatsduring fall and winter. Secondin In eachinstance, fruit wasassociated with other, frequency of occurrencewas black-tailed deer, animal prey and may representfood of other

100 Toweill and Anthony TABLE l. Prey items identified fron 494 bobcat scats{ron Oregon'sCascade Range. Values are number of occurrences;per- cent f.esuencv of occurrencefollors.

Jan-Mar Apr-Jun July-Sep 0ct-Dec {N= 2) iN= r87) (N= 105) (N= 90) lN =494) Prey Item No. Percent No. Percent No. Percent No. Pe.cent

MAMMALS Od.ocoileushenionus 35 3l 30 l6 20 t9 27 I09 22 5 4 4 2 2 2 4 4 l5 3 spitosale srdcitis 0 t 1 0 0 I t 2 0 0 2 I 0 0 2 38 48 26 29 28 30 33 150 ; Ochotonaprinceps 2 2 4 2 8 8 I I 15 3 8 30 l6 IB t7 0 0 57 l2 Thononys nazana I l t0 5 l0 10 2 2 23 5 I I 0 0 0 0 0 0 I Glaucomyssabrinus 5 4 I I I I IO It l7 3 Tamiu ciu rus d.oug lasii 7 6 3 I I 3 3 t8 4 Tanias tounsendii 2 2 1l 6 5 5 7 I 25 2 2 3 2 0 Spermophilus beecheyi 0 0 3 2 2 2 6 Spe rmop hilu s lat eralis 0 0 2 I I I 4 Unknown Sciurid I I I I 2 2 6 3 3 5 3 2 2 1t P ero myscus manicu latus 2 2 l3 7 3 3 22

2 2 6 3 t I II 2 0 0 2 t 2 0 0 5 3 0 l0 2 0 0 2 I 1 I 4 1 0 0 I3 7 1 I l5 3 Microtus ichardsoni 0 4 2 2 2 7 I Mic.otus longicaud.us I 1 4 2 0 0 b I Unknorn cricetid 2 2 t6 9 b 2 2 26 5 0 0 l3 7 0 0 13 3 Scapanustounsendii 0 0 2 I 0 0 2 Neurotrichusgibbsii 0 0 4 2 0 0 4 Sorez troubrid.gii 0 0 3 0 0 0 6 1 I 4 2 0 0 5 0 0 I I 0 0 t 0 t I 0 ; t Unknown Mamnal 5 16 9 7 I 37 , BIRDS 1 I 3 2 3 3 4 4 II 2 (_) 0 0 0 0 1 I I Unlnown Passerine o 9 5 t0 10 4 4 30 6 Eggshell 0 4 2 I t 0 0 5 I REPTILES ScelopotLsoccidental| 00 0000 2 Euneces sLiltonianus 00 0000 Diad.ophispunctatus 00 0000 00 0000 Unknown Snake 00 0000 I n'stcrs 004200115 I FRUIT 33ll252444 33 7

AnnualDiel of Bobcatsin Oregon'sCascade Range l0l animalsingested by bobcats.Human refuse in- kinds of prey (21in summer,19 in fall) and meau cludingplastic sandwich bags, cotton cloth, and prey size(529 g in summerand 539 g in fall) were paper was found in 5 scats. nearlyidentical. Fall and winter diets (SI = weremost similar Discussion 0.942),comprised primarily of snowshoehsres, black-taileddeer, and a varietyof sciuridand Lagomorphsare impo ant preyin bobcatdiets cricetidrodents (Table 2). Bobcat diets changed throughoutthe UnitedStates (McCord and Car- in the spring.Spring dietsincluded all prey eaten doza l9B2) as well as in eastern0regon (Toweill during fall and winter, along with increasedfre- l9B2), severalportions of the Coast Range quency of mountain beaver,ryestern pocket (Schwanzand Mitchell 1945,Nussbaum and gophers (Thomomys mazamal, microtines. Maser 1975)and in the CascadeRange (Nuss- cricetines,and birds. Insectivoresand reptilesoc- baum and Maser 1975,this study).Mountain curredin the springdiet only. The varietyof prey beaverdominated bobcat diets in some(typical- identifiedin the bobcatdiet increasedfrom 17 ly low-elevarion)portions of the Coast Range during the winter to 35 during the spring (Table (Sweeney1978, Witmer and deCalesta1986). 3).Mean prey sizeduring springaveraged 426 g (Table 3), about half that during winter (827 The frequencyof occurrenceof black-tailed g). Wintei and spring diets were the most dis- deerin the diet of bobcatsin the CascadeRange similar(SI = 0,759)of anyseasonal comparison was unexpectedbecause of the size differential (Table2). The second-greatestchange in bobcat of the two species(approximately 6.0 kg vs. 68 diet betweensuccessive seasons occurred be- kg). Many authors have attributed remains of tweensummer and fall (Table 2). Percentagesof deer found in bobcat food habir studies to snowshoehares, black-tailed deer, and sciurids scavenging(Hamilton and Hunter 1939,Rollings in the bobcatdiet increasedfrom summerto fall, 1945,Pollack 1951, Erickson 1955, Progulske with declinein useof mountainbeaver, mice, and 1955, Cashwiler et al. 196l),.In this study, re- birds.Despite the differencein seasonaldiet in- mainsof deerin bobcatscats occurred primari dicatedby a low SI value(0.779), the numberof ly during the fawning period and again during the winter, when alternateprey was probably TABLE 2. Pair-wise diet sinilarity indices for bobcars in least available.However, the high incidenceof Oregon'sCascade Mountain Range. deerin the bobcatdiet during periodswhen alter- nate prey availabilitywas believed to be low leads to speculationthat bobcatsmay prey on deer,as Spring Fall has been suggestedby others(Marston 1942, Spring 0.759 Westfall 1956,McCord 1974,Beasom and Moore 197?,Fritts and Sealandert9?B). The abilityof 0.803 bobcatsto kill adult aswell asfawn deerhas been Fall 0.942 0.770 0.779 well documented(see McCord and Cardoza Annual 0.906 0.935 0.906 l9B2).Major changesin bobcatdiet between warmand cold seasons (winter/spring SI - 0.7591 summer/fallSI = 0.779),were noted in this study. TABLE prev 3. Vari€!y of and weighted nean size of prey Thesechanges were associatedwith a steady identifi€d from 494 bobcat scatscollected from seasonaldecline in prey diversity and increase 0regon'sCascade Range. in weightedmean prey size from springthrough winter (Table3).

Spring Sumner Fall Acknowledgements

Variety of Prey" t7 We thank S. Cehmanand N. T. Weiss who Weighrcd M€an assistedin field work and T. C. Crippen who Prey size (g)! 539 assistedwith thin-layerchromatography. L. N. Carraway,B. J. Verts,and C. Maserassisted in 'Fron Table 1. identificationof specimens.J. W. Thomas,D. S. 'Ungu)ates excluded. deCalesta,W. J. Overton,R. K. Fendall,and

102 Toweilland Anthony r

R. L. Krahmer assistedwith study design.This ing wasprovided by the OregonDep. of Fish and study was conductedunder the auspicesof the Witdlife. This is Agri- OregonCooperative Wildlife ResearchUnit: Ore- cultural Experiment Station Technical Paper gon State University, Oregon Dep. of Fish and 8278. C. Barlow and B. R. Mulligan typed the Wildlife, U. S. Fish and Wildlife Service,and the manuscript,C, H. Nellisand L. J. Nelsonreviewed Wildlife ManagementInstitute cooperating. Fund- the manuscriptand offered helpful comments.

LiteratureCited Major, M., M. K. Johnson,V. S. Davis, and T. F. Ketlogg. 1980. Identifyins scatsby recoveryof bile acids. J. Adorjan,A. S.,and C. B. Kolenosky.I 9. A nanual for id€n- Wildl. Manage. 44:290-293. rification of bairs of selectedOntario nannals. On- Marston, M. A. 1942.Vinter relations of bobcatsto white' tario Dep. Lands For., Res. Rep. (wildl.) 90. tail€d deer in Maine. J. Vildl. Manage. 6:328-337. Beason,S. L., and R. A. Moore.197?. Bobcat food habit Maser,C., B. R. Mate,J. I. Franklin,and C. T. Dlan€ss.l9Bl. responseto a changein prey abundance.Southw. Nar Natuial hislory of Oregon coastlnannals. U.S. For. 2l:451-457. Seru. Gen. Tech. Rep. PNWl33. Erickson, A. V. t955. An ecologicalstudy of rhe bobcat in Mayer,W. V. 1952.The hair ofCalifornia nalnnals wirh keys Michigan. Michigan State Univ., East Lansing.M.S. ro the dorsal guard hairs of mammals. Thesis. Amer. Midl. Nat. 48:480-512. Franklin, J. F., and C. T. Dyrness.t973. Natural v€getation McCord, C. M. 1974.Seleclion ofwinter habitat by bobcats of Oregon and . USDA For. Serv. Gen. (Lynr tufus) on the Quabbin Reservation, Tech. Rep. PNn/-8. Massachusett.J. Mamnd. 55:428437. Fritts, S. H., and J. A. Sealander.t978. Diets of bobcatsin McCord, C. M., and J. [. Cardoza.1982. Bobcat and lynx. Arkansaswith special referenceto age and sex dif- /n J. A. Chapnan and G. A. Feldhaner (eds.).Wild ferences.J. Wildl. Manage. 421533-539. manmals of . Johns Hoptins Univ. Garison, G.4., J. M. Skovlin,C. f,. Poulton,and A. H. Vin- Press,Bahimore, Maryland. Pp. 728-766. ward. 1976.Northw€st plant nanes and symbolsfor Nusbaum, R. A., and C. Maser. 19?5. Food habits of the ecosysteminventory and analysis.4th ed. USDA For. bobcat(Zynr ral.s), in the Coastand Cascaderanges Serv. Cen. Tech. R€p. PNV-46. ofwesrernoregon in relation io presentmanagement Gashwiler,J. S., W. L. Robineti€, and 0. W. Morris. 1961. policies. Northw. Sci. 49:26I-266. Foods of bobcais in Utah and easlern Neyada. J. Pollack, E. M. 1951.Food habits of the bobcat in the New W ildl. Manaee. 24,226-229. England states.J. Wildl. Manage. I5:209-213. Green,G.4., C. W. Witmer, and D. S. deCalesta.1986. NaOH Progulske,D. R. 1955.Cane aninals urilized as food by the preparationo{mannalian predator scatsfor dietary bobcst in the southern Appalachians. J. Wildl. anallsis. J. Marnmal. 67:742. Manage. l9:249-253. Hanilton, V. J. Jr., and R. P. Hunter. 1939.Fall and winter Rollings,C. T. 1945.Habits, foods,and parasitesofthe bob- food habits of Vermont bobcats.J. Wildl. Manage. cal in Minnesota.J. Wildl. Manage.9:l3l-145. 3:99-103. Schwartz,J. E. tl, and G. E. Mitchell. 1945.Th€ Rooseveh "orerlap" Horn, H. S. 1966.Measurement of in conpararive elk on the Olynpic Peninsula,Vashington. J. Wildl. ecologicalstudies. Amer. Nat. 100:419-424. Manage.9:295-3I9. Johnson,M. K., D. R. Aldred, E. V. Clinite,and M. J. Kutilek. Stains,H. J. 1958.Field key to guard hair ofmiddle wesrern I9SL Biochenicalidentification ofbobcai scats.Proc. furbearers.J. Vildl. Manas€. 22:9s-97. BobcatRes. Cont, Nat. Wildl. Fed.,Sci. Tech. Ser. Sweeney,S. J. l9?8. Diet, reproduction,and populationst.uc- 6:92-96. ture of the bobcat (l,yrr rufusfasciatus) in westett Johnson,M. K., R. C. Belden, and D. R. Aldred. 1984.Dif- Washington.Univ. Washington,. M-S. Thesis. f€rentiatingnountain lion and bobcatscats. J. Wildl. Toweill, D. E. 1982.Winter foodsofeastern 0regon bobcats. Manaee. 48:239-244. Northw.Sci. 56:310-315. Jones,J. K. Jr., D. C. Carter, H. H. Cenoways,R. S. Hoff- Vesrfall, C. Z. 1956. Foods earen by bobcarsin Maine. J. nan, and D. W. Rice. 1982.Revised checllisi ofNorth witdl. Manage. 20:r99-200. American mammals north of Mexico, 1982. occas. Vitmer, C. V., and D. S. deCalesra.1986. Resource use by Pap. 80, The Mus., Texas Tech Univ., Lubbock. unerploitedsynpatric bobcatsand coyotesin Oregon. Lahey,J. F. 1979. Clirnate.In R. M. Highsmith Jr. and A. Can. J. Zool. 64.2333-n3a. J. Kinerling (eds.).Atlas of rh€ . Sixth ed. Oregon State Uni!. P.ess, Corvallis. Pp. 43-54.

Receioed.10 September1987 Acceptedfor publication 17 February 19BB

Annual Diet of Bobcatsin Oregon'sCascade Range 103