SHORTCOMMUNICATIONS 377 Wild mammals of North America-biology, management, Pennsylvania,USA. and economics. The John Hopkins University Press, MEALEY,S.P. 1975. The naturalfood habits of free ranging Baltimore,Maryland, USA. grizzly bears in Yellowstone National Park, 1973-1974. , J.S. SUMNER,AND J.A. MITCHELL.1995. The grizzly Thesis, MontanaState University, Bozeman, Montana, USA. bears of Yellowstone: their ecology in the Yellowstone MECH,L.D. 1966. The wolves of Isle Royale. Fauna of the ecosystem, 1959-1992. Island Press, Washington, 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,Wyoming, 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 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 predation America: biology, management, and economics. John on elk 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,Canada. 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 bearsin the western North American ecosystems. 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, Ursus 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. Wolf-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 game 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 meat is one of the most concentrated sources MT59030, USA, email: [email protected] of digestible and available to bears KERRYA. GUNTHER,Bear 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 foraging,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 Hayden Valley 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