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Wild of -biology, management, Pennsylvania,USA. and economics. The John Hopkins University Press, MEALEY,S.P. 1975. The naturalfood habits of free ranging ,, USA. grizzly in Yellowstone , 1973-1974. , J.S. SUMNER,AND J.A. MITCHELL.1995. The grizzly Thesis, MontanaState University, Bozeman, , USA. bears of Yellowstone: their ecology in the Yellowstone MECH,L.D. 1966. The of Isle Royale. Fauna of the , 1959-1992. Island Press, , D.C., NationalParks of the U.S. U.S. GovernmentPrinting Office, USA. WashingtonD.C., USA. DESPAIN,D. 1990. Yellowstone's vegetation: consequencesof NATIONALPARK SERVICE.1984. Fishing Bridge and the history and environment. Roberts Rinehart,Incorporated Yellowstone ecosystem: a report to the director. U.S. Publishing,Boulder, Colorado, USA. Department of the Interior, National Park Service, GREEN,G.I., D.J. MATrSON,AND J.M. PEEK. 1997. Springfeeding YellowstoneNational Park,, USA. on ungulate carcasses by grizzly bears in Yellowstone REYNOLDS,H.W., R.D. GLAHOLT,AND A.W.L. HAWLEY. 1982. National Park. Journalof Wildlife Management61:1040- (Bison bison). Pages 972-1007 in J.A. Chapmanand 1055. G.A. Feldhammer, editors. Wild mammals of North GUNTHER,K.A., ANDR.A. RENKIN.1990. Grizzlybear America: biology, management, and economics. John on calves and otherfauna of YellowstoneNational Park. Hopkins University Press, Baltimore,Maryland, USA. InternationalConference on BearResearch and Management ROE,F.G. 1951. The North Americanbuffalo. University of 8:329-334. TorontoPress, Toronto,. JACOBYM.E., G.V. HILDERBRAND,C. SERVHEEN, C.C. SCHWARTZ, .1970. The North Americanbuffalo. Second edition. S.M. ARTHUR,T.A. HANLEY,C.T. ROBBINS, AND R. MICHENER. University of TorontoPress, Toronto,Canada. 1999. Tropicrelations of brown and black bears in several SCHLEYER,B.O. 1983. Activity patternsof grizzly bears in the western North American . Journalof Wildlife Yellowstone ecosystem and their reproductive behavior, Management63:921-929. predation,and the use of carrion. Thesis, Montana State KNIGHT,R.R., B.M. BLANCHARD,AND P. SCHULLERY.1999. University,Bozeman, Montana,USA. Yellowstonebears. Pages 51-75 in T.W.Clark, A.P. Curlee, SCHULLERY,P. 1992. The bears of Yellowstone. High Plains S.C. Minta, and P.M. Kareiva, editors. Carnivores in Publishing Company, Incorporated,Worland, Wyoming, ecosystems: the Yellowstone experience. Yale University USA Press, New Haven, Connecticut,USA. SHAW,J.H., ANDM. MEAGHER.1998. Bison. Pages 447-466 in MATTSON,D.J. 1997. Use of ungulatesby Yellowstonegrizzly S. Demarais and P.R. Krausman, editors. Ecology and bears, arctos. Biological Conservation81:161-177. managementof largemammals in NorthAmerica. Prentice- , B.M. BLANCHARD,ANDD.R. KNIGHT.1991. Food habits Hall Press, Upper SaddlebackRiver, New Jersey,USA. of Yellowstonegrizzly bears, 1977-1987. CanadianJournal SMITH,D.W., L.D. MECH,M. MEAGHER,W.E. CLARK, R. JAFFE, of Zoology 69:1619-1629. M.K. PHILLIPS,AND J.A. MACK. 2000. -bison MEAGHER,M.M. 1973. The bison of YellowstoneNational Park. interactions in Yellowstone National Park. Journal of U.S. Department of the Interior, National Park Service, Mammalogy81:1128-1135. Scientific Monograph Series No. 1, U.S. Government PrintingOffice, WashingtonD.C., USA. Received: 30 2001. 1978. Bison. Pages 123-133 in J.L. Schmidt and July C.W. Schwartz, editors. Big of North America: Accepted: 19 December 2001. Ecology and management. Stackpole Books, Harrisburg, Associate Editor: Harris.

GRIZZLYBEAR PREDATIONON A BISON CALFIN YELLOWSTONE NATIONAL PARK NATHAN VARLEY,Symbiosis Consulting, P.O. Box 490, Gardiner, Ungulate is one of the most concentrated sources MT59030, USA, email: [email protected] of digestible and available to bears KERRYA. GUNTHER, ManagementOffice, P.O. Box 168, energy protein grizzly YellowstoneNational Park, WY 82190, USA, email: (Ursus arctos horribilis) in the Yellowstone ecosystem [email protected] (Mealey 1975, Pritchardand Robbins 1990, Craigheadet al. 1995). Grizzly bears obtain ungulatemeat primarily Ursus 13:377-381 (2002) throughscavenging winter-killed elk (Cervuselaphus) and bison (Bisonbison) carrion (Craighead et al. 1995,Mattson Key words: bison, Bison bison, grizzly bear, predation, Ursus arctos 1997), usurping wolves (Canis lupus) from their ungu- horribilis late kills (D. Smith, Yellowstone National Park, Wyo- ming, USA, unpublished data), and by predation on elk 378 Ursus 13:2002

calves (Mattson1997). Althoughpredation on elk calves No other bison were visible in the area. Although hills in YellowstoneNational Park (YNP), by bothgrizzly bears blocked the view in some areas, the landscape could be andAmerican black bears (U. americanus),has been well observed for >500 m in all directions, and for a km or documented(e.g., Howell 1921, Johnson1951, Cole 1972, more in most directions. When the cow and calf ap- Craigheadand Mitchell 1982, Guntherand Renkin 1990), proachedthe base of the slope below wherethe bearswere we found no records in the literaturedocumenting bear ,they began to trotpast, the cow in the lead. The predationon bison calves. Although Skinner(1927) re- adultgrizzly, approximately200 metersupslope from the portedthat grizzly bearspreyed on bison calves, he gave bison, stood on her hind legs and looked at the cow and no descriptionto documentthat he actually saw it occur. calf as they trottedpast. The bear then droppeddown to We describe a successful predatoryattack on a bison all 4 legs andran down the slope pursuingthe bison, leav- calf by a grizzly bear in YNP, Wyoming. The event was ing her cubs behind. As soon as the bear began running observed by the senior authorand observed and photo- downslope, the cow andcalf began to runaway. The cow graphedby both a professionalcinematographer (Landis changedposition and ranbehind her calf, keeping herself Wildlife Films, Gardiner,Montana, USA) and a still pho- between the bear and her calf. Within seconds, the bear tographer(Chadwick and Sartore2001). The film foot- had closed the distance and was within a few meters of age allowed repeatedreview by both authors,enabling us the fleeing cow and calf. The chase proceededwest to- to clearly describethe event. We also had an experienced ward the bank of the river and reacheda swale approxi- bison biologist review the videotapedfilm of the preda- mately 1 km from the observerswhere sagebrushand the tion event. low swale partiallyobscured our view. As the bearstarted The kill took place in in central YNP. to pass the cow in pursuit of the calf, the cow whirled Hayden Valley is a large (>8,500 ha) nearly treeless val- aroundand confronted the bear. However,the bearveered ley surroundedby the forested CentralPlateau. Flora in past the cow and continuedchasing the calf. When the 3 the valley consists of sagebrush(Artemisia spp.) and a animalsemerged from the swale, the calf was runningin varietyof forbs,grasses, and sedges (Carexspp.) (Meagher front followed by the bear and then the cow. As the bear 1973). Numerous graminoid-dominatedwetlands are drew near the calf, the calf turnedand ran in tighterand present in the valley. Lodgepole pine (Pinus contorta) tightercircles. The chasemoved back into the swale again, forest types thatoccur on infertilerhyolite soils dominate partiallyobscuring our view. While in the swale, the bear the forestedplateau surrounding Hayden Valley (Despain made contactwith the calf and knockedit down. It made 1990). Spruce(Picea engelmannii)-fir(Abies lasiocarpa) contact again and appearedto bite the calf before jump- standsare interspersed throughout the lodgepolepine zone ing out of the way of the chargingcow, which lowered its in areasof morefavorable moisture regimes such as pond head andtried to hook at the bearwith its horns. The bear margins, north slopes, and drainages (Graham 1978). reappearedfrom the swale holding the calf in its mouth Bison are active in Hayden Valley during all months of with the cow chasing it. The bear stopped, droppedthe the yearand breed and calve in the valley (Meagher1973). calf, and stood its groundover the calf while facing the Grizzlybears are active in the valley throughoutthe non- cow. The cow momentarilystopped pursuingit, but re- denning season from Marchthrough November. mained20-30 metersaway, circling and occasionally rush- The senior authorobserved the event from a vehicle ing in and hooking its horns at the bear. However, the pullout along the GrandLoop Road in Hayden Valley at cow always retreatedquickly when the bear did not run. approximately730 hourson 26 June2000. Observations After the cow stopped chargingat the bear, the bear be- were made with a 40x spotting scope and 8x binoculars. gan to eat the calf. The cow stayed 20-30 meters away An adultfemale grizzly bear accompaniedby 2 cubs-of- and occasionally nibbled grass. After the bear had been the-yearwas foraging approximately2.5 km away, on a feeding on the calf for approximately15 minutes,the cow southwest facing slope on the northeast side of the abruptlyran northand did not return. Yellowstone River. The bear moved throughthe sage- The bearfed on the calf for about30 minutes,then spent brush in a searching patterncommonly observed when approximately10 minutescovering the carcasswith dirt, bearsare huntingfor newbornelk calves, as describedby grass,and sagebrushbranches. By this time, the cubs had Guntherand Renkin (1990) andFrench and French (1990). moved across the slope approximately300 meters to the Several cow elk were scatteredalong the -line 200- east and far uphill from the kill site. The cubs stood up 300 meters upslope from the bears. The 3 bears were often and looked around. The bear then moved directly working their way down slope toward the river as they east upslope to her cubs and led them up a long drawand apparentlysearched the sagebrush for elk calves. We into a forested areaand out of sight. The bear and 2 cubs observeda cow bison andher calf walkingsoutheast along returnedto the carcass at approximately1945 hours that a bench on the northeastside of the riverbelow the bears. evening. The bear uncoveredit and fed on it steadily un- SHORTCOMMUNICATIONS 379 til 2130 hours, when it became too darkto make further Craigheadet al. (1995) studiedgrizzly bearbehavior in observations. The cubs investigated and played around YNP from 1959-70 and documentedgrizzly bears kill- the carcass most of the time theirmother was feeding on ing malnourishedadult bison in spring but did not ob- it. serve predationon bison calves. The InteragencyGrizzly Most bison calves in YNP are born in early May, and Bear Study Team (IGBST) has conducted research on calving is generally over by the end of May, although a grizzly bearsin YNP since 1973 and has not documented few calves are bornas late as September(Meagher 1973). predationon bison calves duringthat 29-year period (M. Based on horn size, body size, and coloration,the bison Haroldson,IGBST, Bozeman, Montana,USA, personal calf killed by the grizzly bear was 7-8 weeks old (M. communication,2001). Long-term(37 years) bison re- Meagher, YNP, Wyoming, USA, personal communica- search and monitoringin YNP also has not documented tion, 2001). It is uncommonfor bison cows with calves bear predation on bison calves (Meagher 1973; M. of that age to be away from mixed herds (females, other Meagher,personal communication, 2001). Extensive re- calves, juvenile males, and often one or more mature views of recentbison literature(Meagher 1986, Reynolds males). Bison cows, especially with calves, are rarely et al. 1982, Shaw and Meagher 1999) found no evidence separatefrom a mixed herd even in winter (Fuller 1960, of grizzly bearpredation on adultbison or calves (but see Meagher1973, Shaw andMeagher 1999). Howeverthere Wyman 2002). In an exhaustive review of historical are exceptions. In the harsh winter environment in sources, Roe (1970) found a credibleaccount of one suc- Yellowstone'sPelican Valley, bison groupsoften disperse cessful grizzlybear kill of a bison cow, butnone on calves. as snow deepens and scatteras individualsor a few ani- Given the extensive documentationin the literatureof mals together,moving into geothermalareas that provide grizzly bearpredation on elk calves, we believe thatpre- the survival margin in the deep snows (Meagher 1970, dationon bison calves is an infrequent,opportunistic event 1973, 1986). An isolated cow with a calf is not rare in or it would have been reportedpreviously. theseconditions. Also, beginningin 1982,the Yellowstone Bison behaviorcoupled with the risks associated with bison populationhas been undergoingmajor changes in predationon bison calves may preclude more extensive distributionand numbers(Taper et al. 2000). As partof use of this resource by bears. We hypothesize that the this, groupsize andcohesiveness has changed,with mixed bison cow and calf were vulnerableto predationdue to herdsdecreasing in size earlierin the breedingseason and being isolated from a herd or mixed group. Most bison bison aggregationsmuch more spreadout. By the sum- arehighly gregarious(Meagher 1973, Shaw andMeagher mer of 1996, there appearedto be a breakingof the more 1999). Situations where cows with calves are isolated usualbison social bonds, even before the end of the grow- fromherds or mixed groupsas in the incidentwe described ing season (M. Meagher,personal communication, 2001). are uncommonexcept for a short period during and im- These changes may have contributedto the presence of mediatelyafter calving (Reynoldset al. 1982). In groups, the apparentlysolitary bison cow with her calf and left adultbison are very formidablein protectingtheir calves. them vulnerableto predation. Gunther(1991) describedan incidentwhere an adultgriz- Injury,disease, or malnutritioncould also have left the zly bear approached19 bison including 5 calves. As the bison cow and calf vulnerable to predation. However, bear approached,the adultbison bunchedtogether into a multiple reviews of the videotaped film did not suggest tight group and stood adjacentto each other facing the that the bison cow was impairedin any way. She did not bear. The calves ran behind the adult bison for protec- limp or appearto be uneven in her gaits. Her agility ap- tion. The bearstopped its approach,sat down and looked peared unimpairedas she changed directionsand turned at the bison, then turnedand walked away. to face the bear. Her physical condition appearedto be Even when isolated from herds, the protectivebehav- prime, with none of the end-of-winterboniness of ribs ior of adultcow bison combinedwith theirsize (318-545 and iliac crest often observed. The condition of her coat kg), sprintingability (66 km/h, Meagher 1986), agility, and timing of the molt were also consistent with those of and horns (Meagher 1973) make them quite formidable a bison in good condition. Nutritioninfluences hair con- when protectingtheir calves, even if the defense is only a ditionand timing of the molt in mammals(Robbins 1983). bluff. In addition,not all behavioralthreats made by bi- At the time of the observation,bison are often still shed- son duringinterspecific interactions are bluffs. McHugh ding wintercoats, which may cling in ragged lighter-col- (1958) observed defensive behavior against humans, oredpatches on top of newly-growingpelage. But a bison horses, ravens (Corvuscorax), a (Antilocapra in poor condition may have much of the winter coat still americana),and a porcupine(Erethizon dorsatum). YNP attached,and look generally unthrifty(M. Meagher,per- files contain one account of a jogger injured by a cow sonal communication,2001). Nothing in the appearance bison with a new calf and multiple accountsof parkvisi- of the bison cow's coat indicatedthat it was malnourished. tors being injured by bull bison almost every year (M. 380 Ursus 13:2002

Meagher,personal communication,2001). In addition, ris, andan anonymousreviewer made substantivehelpful there have been several incidents of horses being gored commentsthat made this a bettermanuscript. We are es- by bison in the park. We hypothesize that the frequency pecially grateful to M. Meagher,who encouragedus to of attemptedgrizzly bear predation on bisoncalves is likely publish this account, sharedher knowledge of bison be- limited by threatsfrom the bison and the potentialfor in- havior, and provided substantiveeditorial comments on jury to predatorybears. the draftmanuscript. A review of the literaturedescribing wolf-bison inter- action may provide some insight into anti-predatorde- fense tacticsbison use againstlarge predators and explain LITERATURECITED why the bison cow turnedto confrontthe bearrather than CARBYN, L.N., S.M. OOSENBRUG, AND D.W. ANIMS. 1993. continue fleeing. Of 45 observed encounters between Wolves, bison, and the dynamicsrelated to the Peace- AthabascaDelta in Canada'sWood Buffalo National Park. groups of YNP bison and wolves, the bison reacted by Canadian Institute, of . tightly grouping38 times (Smithet al. 2000). In 32 of the Circumpolar University CircumpolarResearch Series 4:1-270. 45 observed incidents, the bison stood and faced the CHADWICK,D.H., ANDJ. SARTORE.2001. Grizzlies. National wolves. Of 14 known successful 8 in- predationevents, Geographic200(1):12. volved bison that were impaired. Videotapeof wolf-bi- COLE,G.F. 1972. Grizzlybear-elk relationships in Yellowstone son interactions (D. Smith, personal communication, NationalPark. Journalof WildlifeManagement 36:556- 2001) indicatedthat wolves attemptedto take healthybi- 561. son when the bison were plunging in line in deep snow. CRAIGHEAD,J.J., AND J.A. MITCHELL.1982. Grizzly bear(Ursus As the bison reached solid open ground,the targetindi- arctos). Pages 515-556 in J.A. Chapman and G.A. vidualwould turnand face the wolves, which thenbacked Feldhammer,editors. Wild mammalsof NorthAmerica and economics. John off. In Canada'sWood Buffalo National Park, wolves biology, management, Hopkins UniversityPress, Baltimore, Maryland, USA. often out individuals fromherds (Haynes singled separated , J.S. SUMNER,AND J.A. MITCHELL.1995. The et al. We can infer that grizzly 1982, Carbyn 1993). only grizzly bearsof Yellowstone:their ecology in the Yellowstone bearsare capable of judging theiropportunities and react- ecosystem,1959-1992. IslandPress, Washington, D.C., ing accordinglyto a separatedcow with a calf, especially USA. when the bison are at a disadvantagedownslope from the DESPAIN,D. 1990. Yellowstone'svegetation: consequences of bears. In spite of the speed at which bison can sprint, historyand environment. Roberts Rinehart, Incorporated, they typically react to large predatorssuch as wolves by Boulder,Colorado, USA. AND M.G. FRENCH. 1990. behaviorof standingtheir ground (Smith et al. 2000). This tactic has FRENCH, S.P., Predatory bearbears on elk calves in Yellowstone also been observedto be successfulfor muskoxen(Ovibos grizzly feeding NationalPark. International Conference on BearResearch moschatus;Gunn 1982), (Alces alces: Mech 1966) andManagement 8:335-341. and elk in de- (D. Smith,personal communication, 2001) FULLER,W.A. 1960. Behavior and social organizationof the terring predatory wolves and for bison mixed groups wildbison of WoodBuffalo National Park, Canada. against grizzly bears (Gunther1991). This type of reac- 13:3-19. tion to a threatto her calf, even if a bluff, might explain GRAHAM,D.C. 1978. Grizzly beardistribution, use of habitats, the solitarycow's apparenteffort to keep herself between food habits,and habitatcharacterization in Pelicanand Park. her calf and the bear when initially fleeing and then to Hayden Valleys, YellowstoneNational Thesis, MontanaState Bozeman,Montana, USA. confrontthe bear when it caught up to her and her calf. University, A. 1982. (Ovibos 1021- The incident we described involved a female grizzly GUNN, moschatus). Pages 1035in J.A.Chapman and G.A. Feldhammer, editors. Wild bear with that some cubs have at least cubs, suggesting mammalsof NorthAmerica biology, management,and this behaviorfrom their moth- limitedopportunity to learn economics. JohnHopkins University Press, Baltimore, ers. Although we believe that bear predationon bison Maryland,USA. calves is rare,this incidentindicates that grizzly bearsare GUNTHER,K.A. 1991. Grizzlybear activity and human-induced capable of taking advantageof favorable circumstances modificationsin PelicanValley, Yellowstone National Park. to kill and consume bison calves. Thesis,Montana State University, Bozeman, Montana, USA. , ANDR.A. RENKIN.1990. Grizzly bearpredation on elk calves and other fauna of YellowstoneNational Park. ACKNOWLEDGMENTS InternationalConference on Bear Research and Management 8:329-334. We thankB. Landis of Landis Wildlife Films for pro- HAYNES,G. 1982. Utilizationand skeletaldisturbances of North of his film of this event viding a videotapedcopy footage Americanprey carcasses. Arctic 35:266-281. for our review. C. Schwartz,M. Haroldson,T. Olliff, and HOWELL,B.A. 1921. Theblack bear as a destroyerof game. G. Plumbprovided editorial comments. J. Shaw,R. Har- Journalof Mammalogy2(1):36. SHORTCOMMUNICATIONS 381

JOHNSON,D.E. 1951. Biology of the elk calf (Cervuscanadensis ROE,FG. 1970. The North Americanbuffalo: a critical study nelsoni). Journalof Wildlife Management15:396-410. of the species in its wild state. Universityof TorontoPress, MATTSON,D.J. 1997. Use of ungulatesby Yellowstone grizzly Toronto,Canada. bears, Ursus Arctos. Biological Conservation81:161-177. SHAW,J.H., ANDM. MEAGHER.1999. Bison. Pages 447-466 in MCHUGH,T. 1958. Social behavior of the American Buffalo S. Demarais and P.R. Krausman, editors. Ecology and (Bison bison bison). Zoologica 43:1-40. managementof largemammals in NorthAmerica. Prentice- MEAGHER,M. 1970. The bison of Yellowstone National Park. Hall Press, Upper SaddlebackRiver, New Jersey,USA. Dissertation,University of ,Berkeley, California, SKINNER,M.P. 1927. The predatoryand -bearinganimals of USA. YellowstonePark. Roosevelt Wild Life Bulletin, Volume4, 1973. The bison of Yellowstone National Park. Number2. Roosevelt Wild Life ForestExperiment Station, National ParkService Scientific MonographSeries No. 1. The New YorkState College of Forestry,Syracuse University, . 1986. Bison bison. MammalianSpecies 266:1-8. New York,USA. MEALEY,S.P. 1975. The naturalfood habits of free ranging SMITH,D.W., L.D. MECH,M. MEAGHER,W.E. CLARK,R. JAFFE, grizzly bears in Yellowstone National Park, 1973-1974. M.K. PHILLIPS,AND J.A. MACK. 2000. Wolf-bison Thesis, MontanaState University, Bozeman, Montana, USA. interactions in Yellowstone National Park. Journal of MECH,L.D. 1966. The wolves of Isle Royale. Fauna of the Mammalogy81:1128-1135. NationalParks of the U.S. U.S. GovernmentPrinting Office, TAPER, M.L., M. MEAGHER,AND C.L. JERDE. 2000. The WashingtonD.C., USA. phenology of space: spatial aspects of bison density PRITCHARD, G.T., AND C.T. ROBBINS. 1990. Digestive and dependence in Yellowstone National Park. Final Report. metabolicefficiencies of grizzly and black bears. Canadian U.S. Geological Survey, Biological Research Division, JournalZoology 68:1645-1651. Bozeman, Montana,USA. REYNOIDS, H.W., R.D. GLAHOLT,AND A.W.L. HAWLEY. 1982. WYMAN,T. 2002. Grizzly bear predationon a bull bison in Bison (Bison bison). Pages 972-1007 in J.A. Chapmanand Yellowstone National Park.Ursus 13:375-377. G.A. Feldhammer, editors. Wild mammals of North America: biology, management, and economics. John Received: 27 March 2001. Hopkins University Press, Baltimore,Maryland, USA. 23 ROBBINS, C.T. 1983. Wildlife feeding and nutrition. Academic Accepted: November 2001. Press, Incorporated,Orlando, Florida, USA. Associate Editor: Harris.