SHORTCOMMUNICATIONS Interactions between wolves and female grizzly bears with cubs in Yellowstone National Park A. 3 Kerry Gunther1 and Douglas W. Smith2'4 adult males, solitary adult females, and female grizzly bears accompaniedby yearling or 2-year-old offspring Bear ManagementOffice, PO Box 168, Yellowstone would occasionally usurp wolf-killed ungulates and National WY Park, 82190, USA scavenge the remains. We hypothesized that these 2Wolf PO Box YellowstoneNational Project, 168, Park, cohorts of grizzly bears would be more successful than WY,82190, USA subadultsat usurpingwolf-kills. We furtherhypothesized Key words: Canis lupus, cub bear, mortality, grizzly that due to potential danger to cubs, females with cubs interferencecompetition, interspecific killing, klepto- would not attemptto displacewolf packs from theirkills. Ursus Yellowstone National parasitism, arctos, wolf, Our of interactions between Park monitoring interspecific wolves and bears is From wolf Ursus15(2):232-238 (2004) grizzly ongoing. reintroductionin 1995 until Januaryof 2003, 96 wolf- grizzly bear interactionshave been recorded(Ballard et al. 2003; D. Smith, National Park Service, Yellowstone NationalPark, Wyoming, USA, unpublisheddata). Here we observationsof interactionsbetween wolves Gray wolves (Canis lupus) were extirpated from report and female bears with cubs and evidence of wolf Yellowstone NationalPark (YNP) by the 1920s through grizzly bear cubs near carcasses. Due to predatorcontrol actions (Murie 1940,Young and Gold- packs killing grizzly man 1944, Weaver 1978), then reintroducedinto the grizzly bears' low reproductiverate (Schwartz et al. and statusas a threatened park from 1995 to 1996 to restore ecological integrity 2003) species (USFWS 1993), the effects of wolves on carcass and cub and adhere to legal mandates (Bangs and Fritts 1996, availability survival is an Phillips and Smith 1996, Smith et al. 2000). Prior to importantconsideration for wolf reintro- reintroduction,the potential effects of wolves on the duction and grizzly bear conservationefforts. YNP ha in the states of region's threatenedgrizzly bear (Ursus arctos) popula- encompasses 891,000 tion were evaluated (Servheen and Knight 1993). In Wyoming, Montana,and Idaho,USA. The parkcontains areas where wolves and grizzly bears are sympatric, a variety of habitatsfrom high elevation alpine to low interspecifickilling by both species occasionally occurs elevation sagebrush grasslands (Despain 1990). YNP (Ballard 1980, 1982; Hayes and Baer 1992). Most and the surroundingarea (GreaterYellowstone Ecosys- agonistic interactionsbetween wolves and grizzly bears tem, GYE) support an estimated 56,100 elk (Cervus involve defense of young or competition for carcasses elaphus), 29,500 mule deer (Odocoileus hemionus), (Murie 1944, 1981; Ballard 1982; Horbeck and Horejsi 5,800 moose (Alces alces), 3,900 bighorn sheep (Ovis 1986; Hayes and Mossop 1987; Kehoe 1995; McNulty canadensis), 3,600 bison (Bison bison), and smaller et al. 2001). Servheen and Knight (1993) predictedthat numbers of whitetail deer (Odocoileus virginianus), reintroduced wolves could reduce the frequency of mountaingoat (Oreamnosamericanus), and pronghom winter-killed and disease-killed ungulates available antelope (Antilocapra americana) (U.S. Fish and for bears to scavenge, and that grizzly bears would Wildlife Service 1994). Large carnivores in the GYE occasionally usurp wolf-killed ungulate carcasses. include grizzly bears, American black bears Servheen and Knight (1993) hypothesized that in- (U. americanus), wolves, and mountain lions (Felis terspecific killing and competition for carcasses would concolor). In 2002, the reintroducedwolf populationin have little or no populationlevel effect on either species. the GYE was estimated at 273 wolves in 31 packs As a component of post-reintroductionwolf and (Smith et al. 2003a). More than 90% of the prey killed grizzly bear monitoringprograms, interspecific interac- by wolves in the GYE is elk (Smith et al. 2003b). Other tions between the species were recorded.We expected prey species killed by wolves include deer, bison, and reintroducedwolves to occasionally kill grizzly bears, moose, but individually none of these prey comprise especiallycubs-of-the-year (cubs). We also predictedthat >2% of GYE wolves' diet. The GYE grizzly bear populationis estimatedat 280-610 bears (Eberhardtand Knight 1996). The GYE is unique among areas [email protected] [email protected] inhabited by grizzly bears in North America because 232 SHORTCOMMUNICATIONS 233 Fig. 1. An interaction between gray wolves and a female grizzly bear with 2 cubs-of-the-year in Pelican Valley, Yellowstone National Park,Wyoming, USA, 2000. The wolves are on the bank of the creek, which is 2-3 meters higher than the bears in the creek bottom. This makes the wolves appear larger in proportion to the bears than they were (photo by D. Smith). of the substantial consumption of ungulate meat by observed interactingwith wolves. Only 7 (7%) inter- bears (Mattsonet al. 1991, Mattson 1997). Priorto wolf actions between wolves and females with yearlings or reintroduction,GYE grizzly bears obtained ungulate two-year olds were recorded. meat primarily by scavenging winter-killed elk and Of the 8 interactions between wolves and female bison carcassesin spring (Greenet al. 1997), by preying grizzly bears with cubs, 5 were at carcasses, 2 were at on elk calves in late spring and early summer (Gunther wolf rendezvoussites, and 1 occurredat a neutralsite. In and Renkin 1990), and by preying on and scavenging 3 of the 5 interactionsat carcasses(Observations 1, 5, 8; rut-weakened and rut-killed elk and bison in late Table 1), the bear family groups were displaced by summer and fall (Mattson 1997). wolves regardlessof the numberof wolves present(1-5 wolves). In 1 of these interactions(Observation 1; Table 1), a larger bear, probably a male, was feeding on the Interactionsbetween wolves and carcass before the female with cubs approached.After female grizzlies with cubs the lone bear left the carcass, a wolf fed on the carcass From 1995 through 2002, 96 wolf-grizzly interac- and the female with cubs left the area.The outcome of 1 tions were recorded (Ballard et al. 2003, D. Smith, interactionnear a carcass was neutral (Observation2; unpublished data). Only 8 (8%) of these interactions Table 1; Fig. 1). A female grizzly with 2 cubs were between wolves and female grizzly bearswith cubs encountered 4 adult wolves that were walking away (Fig. 1). Females with older offspring were also rarely from the carcass of a bull elk that was being controlled Ursus 15(2):232-238 (2004) 234 SHORTCOMMUNICATIONS Table 1. Interactions between wolves and female grizzly bears with cubs in Yellowstone National Park, 1995-2002. Dominant Observation Date Bears Wolves Location species 1 6 Aug 1998 Adultfemale, 1 cub 1 adult Carcass Wolf 2 12 Jul 2000 Adultfemale, 2 cubs 4 adult Carcass Neutrala 3 17 Jun 2001 Adultfemale, 2 cubs 4 adult,2 yearlings Carcass Bear 4 11 May2002 Adultfemale, 2 cubs 1 adult, 1 yearling n/a Bear 5 22 May2002 Adultfemale, 1 cub 1 adult,2 yearlings Carcass Wolf 6 31 Jul 2002 Adultfemale, 3 cubs 5 adult,3 pups Rendezvous Wolf 7 8 Aug 2002 Adultfemale, 3 cubs 3 pups Rendezvous Neutral 8 21 Sep 2002 Adultfemale, 1 cub 2 adult, 1 yearling, Carcass Wolf 2 unknown alone adultbear had possession of bullelk carcass, female with2 cubs walkingtoward the carcass interactedwith 4 wolves leaving the carcass. by a single grizzly bear. After a brief standoff, the harassed them. At 0734 hours, after feeding on the wolves continued walking away from the carcass and carcass for about 48 minutes, the bears left the kill and the female with cubs continued walking toward the walked away to the southwest. The wolves did not carcass. Although the interactionwith the wolves was harassthe bears as they left. None of the bears was hurt. neutral,the female with cubs did not attemptto usurpthe Two encountersbetween wolves and female grizzly carcass from the single adult bear. bears with cubs were observed at wolf rendezvoussites. In the other interactionat a carcass (Observation3, In late July 2002 (Observation 6, Table 1), 5 adult Table 1), a female with 2 cubs successfully usurped wolves and 3 wolf pups were at their rendezvous site a carcass from 6 wolves. On 17 June 2001 at 0606 when a female grizzly with 3 cubs walked throughthe hours,6 membersof the DruidPeak pack were observed site. One wolf approachedthe bears and followed them in LamarValley feeding on the carcassof a cow elk they out of the area and no furtherinteractions ensued. One had probably killed the previous night. The 6 pack week (Observation7, Table 1) later, the same 4 bears members present included radiomarkedwolves 21 (the walked through the same wolf rendezvous site when alpha male) and adults 106F, 217F, and 224M, as well only the 3 wolf pups were present. The pups fled the as two unmarkedyearlings. The remaining20 adult and area upon sighting the bears;the bears left the area with yearling wolves of the pack were not at the carcass, nor no visible response to the pups. were the 11 pups from two litters. At 0614 hours, an One other interactionbetween wolves and a female adult female grizzly bear with 2 cubs was observed grizzly bear with cubs did not involve a carcass or approachingthe carcass from the west. When the bears rendezvoussite (Observation4, Table 1). A female with neared the carcass, the wolves circled and confronted 2 cubs was walking within 1 km of a wolf den site when them. As the bears faced wolves that were directly in 2 wolves approachedher. The adult bear charged at the frontof them, other wolves rushedin and bit at the bears wolves. The wolves stoppedtheir approach and retreated from behind. The cubs stayed directlybeside or beneath but did not leave the area. The female and cubs left the theirmother as she slowly continuedtoward the carcass. area, and no other interactionwas recorded. Periodically, the female stopped to protect herself and lunged and swatted at the wolves. At times all 3 bears lunged togetherat an approachingwolf; other times the adult or cubs lunged independently at approaching Interspecific killing of grizzly wolves.