ENCOUNTERCOMPETITION BETWEEN BEARS AND COUGARS: SOMEECOLOGICAL IMPLICATIONS

KERRYM. MURPHY,Hornocker Wildlife Institute, P.O. Box 526, MammothHot Springs,WY 82190, USA, email: kmurph@ gomontana.com GREGORYS. FELZIEN,'Hornocker Wildlife Institute, 3246, UniversityStation, Moscow,ID 83843, WA, USA MAURICEG. HORNOCKER,Hornocker Wildlife Institute, P.O. Box 3246, UniversityStation, Moscow,ID 83843, USA, email: [email protected] TONIK. RUTH,Hornocker Wildlife Institute, 3246, UniversityStation, Moscow,ID 83843, WA, USA, email: RUTH8744@NOVELL. UIDAHO.EDU

Abstract: Black bears (Ursus americanus)or grizzly bears (Ursus arctos) visited 8 of 55 cougar-killed (Felis concolor) ungulates in Glacier National Park(GNP), Montana,from 1992 to 1995, and 19 of 58 cougarkills in Yellowstone NationalPark (YNP), Wyoming, from 1990 to 1995. Bears displaced cougars from 4 of 8 carcasses they visited in GNP and 7 of 19 in YNP. Cougar predationprovided an average of 1.9 kg/day (range= 0-6.8 kg/day) of biomass to bears that fed on cougar-killedungulates. This biomass was an importantpercent (up to 113%) of the daily energy needs of bears when comparedto their caloric requirementsreported in the literature. We suggest that ungulate carrionresulting from cougar predationis importantnutritionally to bears in some regions and seasons. Cougars that were displaced from their kills by bears lost an average of 0.64 kg/day of ungulatebiomass, or 17-26% of their daily energy requirements. Biologists modelling or measuringcougar predation rates should be aware that losses to scavengers may be significant.

Ursus 10:55-60

Key words: black bear, competition, cougar, Glacier National Park, grizzly bear, predation, Puma concolor, scavenging, Ursus americanus, Ursus arctos, Yellowstone National Park.

Encountercompetition is a form of interferencecom- documentthe frequencythat cougars were displacedfrom petitionthat occurs when 1 or more mobile, nonspatially- ungulateprey and calculate the quantityof biomass that attachedindividuals are harmedas they directlypursue a cougars lost to bears. common resource (Schoener 1983). This harmincludes Ourresearch was fundedby G.C. Hixon, M.J.Murdock injuriesresulting from physical interactions,loss of time, CharitableTrust, Montanaof Fish, Wildlife and Parks, or theft of food. For carnivores,the disputed resource Nathaniel P. Reed, the P.W. Busch Family Foundation, may be prey that a subordinatecarnivore has killed and a The NationalFish andWildlife Foundation,The National dominantcarnivore intends to scavenge. Geographic Society, The National Wildlife Federation, Interactionsbetween cougarsand scavengersthat were The R.K. Mellon Foundation,the U.S. Fish and Wildlife presentnear cougar-killed prey have been reported(Boyd Service, and Yellowstone National Park. The Gallatin and O'Gara 1985, Spreadbury 1989, White and Boyd National Forest, GardinerRanger District, and Glacier 1989, Harrison 1990, Green 1994). Koehler and National Park provided logistical support. We thank J. Horocker (1991) found 4 bobcats (Lynx rufus) and 2 Cole, T. Fredrickson,B. Holmes, M. Johnson,J. Jonkel, coyotes (Canislatrans) killed by cougarsnear prey cache J. Murnane, B. O'Gara, T. Parker, S. Relyea, J. sites. Harrison(1990) found that a maternalfemale cou- Tischendorf, and B. Wiesner for their work in the field where gar residing coyote abundance was reduced by or laboratory. B. Chapman and D. Stradley provided humans killed ungulate prey less frequentlythan a ma- aerial support on short notice. P. Munholland played ternalfemale where living coyote numberswere not ma- an important role in designing the cougar predation nipulated. Coyotes displacedcougars from theirkills less studies. D. Pac graciously provided his unpublished frequentlywhere coyote numberswere controlled. data on the weights of mule deer carcasses. We thank Althoughinteractions between cougarsand scavengers agency personnel S. Frye, G. Green, T. Lemke, J. near have been cougar-killedprey documented,the eco- Mack, J. Logan, C. Sime, T. Their, D. Tyers, J. Varley, logical importanceof encountercompetition remains un- and R. Wuertz. We especially thank K. Aune and T. clear. Our was objective to (1) documentthe frequency Moore of the Montana and Wyoming wildlife labora- that black bears and bears used grizzly cougar-killedun- tories, respectively, for their technical support and estimate the biomass gulates, (2) ungulate made avail- guidance. We thank I. Ross and an anonymous per- able to bears as a result of cougar predation, and (3) son for reviewing this manuscript.

1Deceased. 56 Ursus 10:1998

STUDYAREAS 1992-95, in GNP and during spring-autumn,1990-95, in YNP. Using methods reportedby Shaw (1977), cou- GlacierNational Park gars were located 1-3 times daily, between 0600 and Cougar-bearinteractions were documentedconcurrent 2300 hours from the ground or from airplanes,without with studies of cougar-wolf (Canis lupus) relationships disturbing them. All location sites were intensively in a 790-km2area along the North Fork of the Flathead searched by walking the contours of slopes at 1-20 m River in GlacierNational Park (GNP) in northwestMon- intervals to locate carcasses after cougars left. Track- tana. Cougars preyed on elk (Cervus elaphus), white- ing hounds were used to assist searches of locations tailed deer (Odocoileus virginianus), moose (Alces and to trail cougars between location sites. Intact un- alces), and mule deer (Odocoileus hemionus). The val- gulate carcasses were necropsied to distinguish cougar ley was gently rolling terrainsupporting a montanefor- predationfrom that of other carnivoresby looking for est interspersedwith meadows. It was borderedby steep gross pathology or feeding behaviors described in mountains, 1700-3000 m in elevation. Snow accumu- O'Gara (1978), Wade and Bowns (1982), and Alberta lation promptedungulates to winter at elevations <1600 Agriculture(1990). Cougars were monitored on con- m from late November to April. Thereafter,ungulates secutive days until at least 2, but typically 4 ungulates used progressivelyhigher elevations associated with phe- were killed. We attemptedto document all ungulates nological changes in vegetation. killed by cougars during this period, called a predation Black bears and grizzly bears were common. Some sequence. grizzlies were active outside their dens for at least part of the winter, particularlyin the Kintla Lakes area of BearVisits to CougarPrey GNP, where carrionwas relatively abundant. Bear visits to cougar-killedungulates were detected by observing bears or by noting the presence of bear YellowstoneNational Park scats, hair, or tracks near carcasses. Hair samples of Cougarswere studied in the northernportion of Yel- carnivores were identified to genus or species by per- lowstone National Park (YNP), Wyoming, and the con- sonnel at the Wyoming Game and Fish Laboratoryin tiguous ParadiseValley of south-centralMontana. The Laramie,following Moore et al. (1974). We could not winter density of adult-subadultsranged from 2.1 to 3.5 always discernthe species of bear that used cougarprey. per 100 km2 on a 662-km2core area where they spent Displacementof cougarsfrom cougarkills was recorded wintermonths on ungulateranges between 1550-2500 m. as a special case of bear visitation. To identify dis- Elk and mule deer were far more abundantthan moose placement,we comparedthe weight of the ungulatecar- and white-taileddeer. Winteringelk counts rangedfrom cass that remained(after use by the bear) to the amount 9,400 to 19,000 from 1990 to 1995 (Mack and Singer present,on average, after cougars left kills without bear 1992; J. Mack, YNP, unpubl. data). Mule deer counts displacement. When possible, we interpretedtracks of and radiotelem- ranged from 1,600 to 2,500 between 1990 and 1994 cougars and bears visible in the snow (Lemke 1994). Duringlate spring,summer, and autumn, etry data to discern bear displacement. used elevations to 2900 m and on un- cougars up preyed Bears gulates that were dispersedrelative to theirrestricted dis- Biomass Eaten by tributionin winter. Ungulateranges supportedmontane We estimated the wet ungulate biomass eaten by kills in YNP. forest, sagebrushsteppe, and grasslandsteppe. bears (BEB) feeding on cougar only if A minimum of 236 grizzly bears were present in the Biomass was considered available to bears only the 20,000-km2Greater Yellowstone Ecosystem in autumn we detected bears at a cougar kill. BEB was of the 1992 (U.S. Fish and Wildl. Serv. 1993, Eberhardtet al. difference between the live-weight ungulate 1994). Black bears were commonly observed. Bears and the amount consumed by the cougar, multiplied used dens from mid-Novemberto mid-April. by the estimated fractional consumption of carcasses by bears. To approximate the energy content of BEB, we converted BEB to its caloric equivalent by METHODS assuming dry weight was 32.4% of wet weight (Robbins et al. 1974, Robbins 1993) and multiply- DocumentingCougar Predation ing dry weight by its digestible energy of 4.6 kcal/g BEB for each kill was Responses of bears to ungulates killed by (Mealey 1975). cougar and divided the radiocollaredcougars were documented during winter, summed to estimate total BEB by BEARS AND COUGARPREDATION * Murphyet al. 57 length of the predation sequence in days to estimate on a small numberof observations,(2) coyotes, avifauna, daily BEB. decomposers,tissue autolysisand decay, andwater evapo- Weightsof UngulatePrey.-The weights of ungulates ration reduced carrionbiomass, particularlyif bears in- killed by cougars were estimatedusing age-specific and termittentlyfed over extendedperiods (>3 days) on cougar sex-specific growth models constructedfrom empirical kills, and(3) >1 bearmay have fed fromcarcasses. There- data on live and field-dressedweights (Greerand Howe fore, BEB values were crudeestimates of individualbear 1964; D. Pac, unpubl.data). Field-dressedweights were consumption. correctedfor loss of viscera using coefficients obtained from Quimby and Johnson (1951) or calculated from Biomassthat Cougars Lost Andersonet al. (1974). Birthweights and dates of partu- The biomass cougars lost (BCL) was estimated when rition were estimatedfrom Johnson (1951), Robinetteet bearsdisplaced cougars from cougarkills. The fractional al. (1973), Pac et al. (1991), or elk calf mortalitystudies consumptionby cougarswas multipliedby estimatedlive (J. Mack, YNP, unpubl.data). Weight maxima,minima, weight of the ungulateto predictthe biomass that would rates of weight loss in winter, and rates of weight gain in have been consumed if cougars had not been displaced. spring-summer were obtained from Johnson (1951), The estimatedbiomass the cougarconsumed before it was Greer(1965), Robinetteet al. (1973), and Andersonet al. displaced(daily consumptionrate multiplied by the num- (1974). Ages were estimatedfor deer and elk using tooth ber days the cougarwas presentat the kill) was subtracted replacementand wear patterns(Quimby and Gaab 1957, from this predicted cougar consumption to determine Robinetteet al. 1957). BCL. BCL for kills was summedfor predationsequences CougarConsumption.-The ungulatebiomass cougars to estimate total BCL and divided by the length of a se- consumed from their kills was estimated as the product quence to estimatedaily BCL. Total BCL for sequences of the daily cougar consumption(specific to cougar so- was less than total BEB because bears often scavenged cial class) and the days the cougar remainedat the car- cougar kills that cougars had alreadyabandoned. cass. Daily consumption was estimated by subtracting the weight of uneaten portions of ungulates from esti- mated live weights and dividing by the numberof days RESULTS (to the nearest0.5 day) thatthe cougarfed. Daily cougar Fifty-five ungulateswere killed by cougarsin GNP and consumption was independently determined from in- 58 in YNP (Table 1). Fifteen (27%) of 55 ungulatekills stances when scavengersdid not use cougar kills. in GNP occurredin the Kintla Lakes area where bears Portionof UngulatesEaten by Bears.-Bear consump- were often active outside their dens during the winter. tion was estimatedat 50% of cougar-killedelk based on Of these 15 kills, 5 were visited by grizzlies (3 cases of 3 visual estimatesmade by Green(1994). Bear consump- displacement)and 2 by an unknownbear species (1 dis- tion of deer was estimatedat 93%, based on a visual esti- placement). Bears visited 42% (n = 26) of cougar kills mate made by Green (1994), 2 estimates in this study, we monitored in YNP during spring, 25% (n = 24) in and 2 estimates calculatedby subtractingestimated cou- summer,and 25% in autumn(n = 8). Visitation during gar consumption and weights of carcass remains from spring was greaterthan summerand autumncombined, live weights of deer fed on by bears. Our estimates of but not significantlyso (X2= 1.95, P = 0.09, 1-sidedtest). bear consumptionwere imprecise and probablyover-es- The mean total BEB for predationsequences in YNP timatedindividual bear use because (1) they were based was 45 kg (SD = 55, n = 11). The range was from

Table 1. Frequencies bears visited or displaced (disp.) cougars from cougar-killed ungulates, Glacier National Park, 1992- 95, and Yellowstone National Park, 1990-95.

GlacierNational Park YellowstoneNational Park (winter, n = 55) (spring-autumn,n = 58)

No. visitsa(%) No. disp.(%) No. visitsa(%) No. disp.(%) Black bear 0 (0) 0 (0) 8 (14) 4 (7) bear Grizzly 6 (11) 3 (5) 1 (2) 1 (2) Unknown bear 2 (4) 1 (2) 10 (17) 2 (3) a Visits include instances when bears displaced cougars from cougar kills. Data for visitation by bears that were not associated with predation sequences were included. 58 Ursus 10:1998 zero kg during a 55-day sequence to 157 kg in 23 days. fully defend at least some of their kills from challengers The mean daily BEB was 1.9 kg/day (SD = 2.5, n = 11, or cope with encountercompetitors by feeding on their range = 0-6.8). prey between periods of use by dominantspecies. The mean total BCL for predationsequences was 16 Infrequentbut windfall feeding opportunitiesfor bears kg (SD = 31, n = 11). The rangewas from zero kg during on cougar-killedungulates were suggested by the high a 55-day sequence to 94 kg in 20 days. The mean daily standarddeviation (SD = 55) of the total BEB for preda- BCL was 0.64 kg/day (SD = 1.4, n = 11, range = 0-4.7). tion sequences relative to its mean (45 kg). BEB was Daily consumptionrates of cougars averaged 8.5 kg/ zero kg for 27 of 38 cougar-killedungulates found dur- day for subadults (self-sufficient cougars <24 months) ing predation sequences. However, the ungulate and nonmaternalfemales combined(n = 7 cougars), 16.7 biomass availableto bearswas potentiallysignificant en- kg/day for family groups(n = 5 groups), and 13.8 kg/day ergetically to them. The mean daily BEB (1.9 kg/day) for an adult male. Prey consumptionby cougars aver- convertedto about2,830 kcalday. This value represented aged 82% by subadultsand 46% by adults (n = 12 cou- 71% of the 4,000-kcal/day energy budget of a gars). Cougar predationrates averaged 1 ungulate/8.7 nonhiberating103-kg captive black bear (David 1987), days (SD = 4.1, n = 11 sequences; 11 cougars). and equaled 113% of the 2,500-kcal/daybudget of a hi- berating, 204-kg captive grizzly bear (Wattsand Jonkel 1988). DISCUSSION The daily BEB was highest when cougars killed large Bears in our study areas used cougar kills frequently. (>80 kg) ungulates and bears visited a high numberof Although reportsof bear-cougar interactionsare nearly cougar kills during a sequence. The highest daily BEB absentfrom the literature,we found about 1 in 7 cougar- (6.8 kg/day) occurredwhen a female cougar accompa- killed ungulateswere scavenged by bears in GNP and 1 nied by 2 large (42 and 55 kg) kittenskilled 4 elk (2 large in 3 in YNP. Bears displacedcougars from about 1 in 14 calves and 2 cows) in 23 days. Bears visited 3 of these kills in GNP and 1 in 8 kills in YNP. Consideringonly kills and displacedthe cougars once. We estimatedthat the Kintla Lakes area of GNP, bears visited about 1 in 2 bears obtained 157 kg of carrionduring this sequence. cougar kills and displaced them from 1 in 4 kills during BEB values were crude estimates because we lacked wintermonths. Green(1994) documentedthat bears vis- adequate data concerning consumption of cougar- ited 3 of 14 cougar-killedungulates (1 displacementby a killed prey by bears. More than 1 bear may have fed grizzly bear) in northernYNP. on individual cougar kills. We also did not evaluate We assume thatthe frequencywith which bears detect the direct and indirect energy costs and benefits, or cougar-killedprey is highest where ungulates, cougars, the risks of injury, associated with obtaining this food andbears exhibit strongspatial overlap and occur at high relative to alternative foraging strategies available to densities. Because bears and cougars use low elevation bears. Therefore, we can only hypothesize that cou- habitatsduring the springin the mountainousportions of gar-killed prey provided significant energy gains to the northwestern United States and western Canada bears. (Seidenstickeret al. 1973, Murphy1983, Servheen 1983, Interactions between cougars and other carnivores Logan and Irwin 1985, Mack 1988, Raine and Kansas at cougar kills may directly influence the behavior and 1990, this study), encountercompetition between bears survival of dominant competitors. Bears may develop and cougars may increase during spring in this region. behaviors that, over long periods (>2 weeks) increase Our YNP data weakly supported(P < 0.09) that bears their likelihood of detecting cougar kills. For example, visited cougarkills more frequentlyin springthan during the habitat selections and activity schedules of bears summerand autumn. may be altered if they predictably and more efficiently The absence of elaboratecaching (e.g., in the trees) by obtain food through encounter competition than cougars supportsthe hypothesis that frequentresponses throughalternative foraging strategies. Bears may also by ursidsand canids to cougar-killedprey are not univer- temporarily change their behavior in direct response sal. Although large felids cache more extensively than to carrion they have discovered. Bear survival may small ones, food cachingis not as commonor stereotyped be reduced if the prospective food rewards provide in felids as in canids (Kleimanand Eisenberg 1973). Fre- sufficient incentive for them to take risks. We found quent displacementby scavengerscould provide natural 5 coyotes that were killed by cougars near cougar- selection for more elaboratecaching of kills by cougars. killed ungulates. Boyd and O'Gara(1985) and Koehler Alternatively,it may suggest that cougars can success- and Hornocker (1991) made similar observations. BEARS AND COUGARPREDATION * Murphyet al. 59

Mean daily BCL (0.64 kg/day) was surprisinglyhigh, giving them a competitive edge over felids in detecting about 26% of the 2.2-2.7 kg/day requiredfor a single carrion. adult female cougar, or 17% of the 3.4-4.3 kg/day re- Although it appears that encounter competition con- quired for a single adult male cougar as estimated from fers effects that are negative on cougars and positive on an energetics model (Ackermanet al. 1986). The high bears, some proximateand ultimate benefits to cougars standarddeviation (SD = 31) of total BCL relative to its may result from encounterand exploitationcompetition mean (16 kg) suggested that losses by cougars to bears between cougars and their co-evolved competitors. For were sporadic. example, although spacing in cougar territoriesis prob- The cougar's solitary natureand predatoryspecializa- ably driven indirectly by interspecific competition for tion on large vertebrateprey may predispose it to the the resources that space provides, displacementof cou- adverse effects of displacement. Cougars may lose a gars from their kills by other carnivores could further considerable energy investment when displaced by an enhance spacing and decrease the likelihood that indi- aggressive scavengeror may incurinjuries when defend- vidual cougars might deplete their local food supplies. ing their kills. Cougar death due to interspecific fight- ing with scavengersat cougarkills has been documented (White and Boyd 1989). The alternativeof killing ad- LITERATURECITED ditional prey to compensate for losses to scavengers, ACKERMAN, B.B., F.G. LINDZEY, AND T.P. HEMKER. 1986. however, also carries energetic costs and risk of injury. 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