A polar bear (Ursus maritimus) was observed unsuccessfully stalking and chasing caribou (Rangifer tarandus) in western Hudson Bay. Before chasing the caribou, the polar bear appeared to make use of wind direction and vegetation cover in order to move close to them. While there have been very few documented cases of the two species interacting, our observations indicate that polar bears will stalk and chase caribou.On a observé un ours polaire (Ursus maritimus) traquer et poursuivre sans succès le caribou (Rangifer tarandus) dans l'ouest de la baie d'Hudson. Avant de se lancer dans sa poursuite, l'ours polaire semblait s'aider de la direction du vent et du couvert végétal pour s'approcher des animaux. Bien que très peu de cas d'interaction des deux espèces aient été documentés, nos observations révèlent qu'en réalité les ours polaires traquent et poursuivent le caribou

Brook, Ryan K.

Richardson, Evan S.

English

University of Calgary Journal Hosting

ARCTICVOL. 55, NO. 2 (JUNE 2002) P. 193–196Observations of Polar Bear Predatory Behaviour toward CaribouRYAN K. BROOK1 and EVAN S. RICHARDSON2(Received 20 December 2000; accepted in revised form 13 September 2001)ABSTRACT. A polar bear (Ursus maritimus) was observed unsuccessfully stalking and chasing caribou (Rangifer tarandus) inwestern Hudson Bay. Before chasing the caribou, the polar bear appeared to make use of wind direction and vegetation cover inorder to move close to them. While there have been very few documented cases of the two species interacting, our observationsindicate that polar bears will stalk and chase caribou.Key words: polar bear, Ursus maritimus, caribou, Rangifer tarandus, predation, Hudson Bay, Manitoba, Wapusk National ParkRÉSUMÉ. On a observé un ours polaire (Ursus maritimus) traquer et poursuivre sans succès le caribou (Rangifer tarandus) dansl’ouest de la baie d’Hudson. Avant de se lancer dans sa poursuite, l’ours polaire semblait s’aider de la direction du vent et du couvertvégétal pour s’approcher des animaux. Bien que très peu de cas d’interaction des deux espèces aient été documentés, nosobservations révèlent qu’en réalité les ours polaires traquent et poursuivent le caribou.Mots clés: ours polaire, Ursus maritimus, caribou, Rangifer tarandus, prédation, baie d’Hudson, Manitoba, parc national WapuskTraduit pour la revue Arctic par Nésida Loyer.1 Natural Resources Institute, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada; umbrook1@cc.umanitoba.ca2 Canadian Wildlife Service, 5320-122 St., Edmonton, Alberta T6H 3S5, Canada; Evan.Richardson@ec.gc.ca© The Arctic Institute of North AmericaINTRODUCTIONPolar bears (Ursus maritimus) feed primarily on the ringedseal (Phoca hispida) and to a lesser degree on other marinemammals, including bearded seal (Erignathus barbatus),beluga whale (Delphinapterus leucas), narwhal (Monodonmonoceros), and walrus (Odobenus rosmarus) (Stirlingand Archibald, 1977; Lowry et al., 1987; Smith, 1980;Smith and Sjare, 1990; Rugh and Shelden, 1993; Stirlingand Øritsland, 1995). However, some populations of bearsare forced onto land during the summer months by thecomplete or partial melting of the sea ice, which limitstheir access to seals (Stirling et al., 1999). Polar bears arewell adapted to fast through these onshore periods (Wattsand Hansen, 1987), but they do feed opportunisticallyduring this time. While polar bears are known to useterrestrial food sources (Russell, 1975; Abraham et al.,1977; Stempniewicz, 1993; Donaldson et al., 1995; Smithand Hill, 1996), urea/creatinine ratios (Ramsay et al.,1991), stable-carbon isotope analyses (Ramsay and Hobson,1991; Hobson and Stirling, 1997), and behavioural obser-vations (Knudsen, 1978; Lunn and Stirling, 1985) suggestthat terrestrial environments form only a minor componentof their diet.Grizzly bears (U. arctos), close relatives of polar bears(Kurtén, 1964) with similar physiology and morphology,are known to be effective predators of caribou (Rangifertarandus) (Boertje et al., 1988; Young and McCabe, 1997)and occasionally muskox (Ovibos moschatus) (Gunn andMiller, 1982; Case and Stevenson, 1991; Clarkson andLiepens, 1993). However, there are few records of polarbear predation on large terrestrial mammals. Derocher etal. (2000) documented several observations of polar bearspreying on Svalbard reindeer (R. t. platyrhynchus).Ovsyanikov (1996) noted a muskox that may have beenkilled by a polar bear. F. Miller (pers. comm. 2000)observed a female polar bear with cubs chasing muskoxand caribou on Bathurst Island. An Inuk from Resolutetold I. Stirling of a muskox killed on the sea ice by a polarbear, and an Inuk from Tuktoyaktuk told him of a polarbear unsuccessfully chasing reindeer on the TuktoyaktukPeninsula along the southern Beaufort Sea (I. Stirling,pers. comm. 2000). This paper describes observationsmade of a polar bear stalking and chasing caribou inWapusk National Park, Manitoba, 3 km inland from theHudson Bay coast. Our observations were madeopportunistically, during a vegetation sampling project,from a tower ~3.5 m above ground level.DESCRIPTION OF OBSERVATIONAt 20:15 local daylight time on 16 July 1998, a subadultpolar bear of unknown sex was observed approaching agroup of approximately 120 grazing caribou. The windwas blowing from the north-northwest at approximately20 km/h, and the bear was 500 m downwind.  The beargenerally kept its head down, below shoulder level, stop-ping every five seconds to face the caribou as it ap-proached. The bear moved slowly along the inside edge of194 • R.K. BROOK and E.S. RICHARDSONthe nearby lake within the 2 m tall willow fringe. The bearbriefly moved its head partially out of the willow fringedirectly facing the caribou and then remained in the wil-lows while slowly stalking the herd over the next 20minutes. During this time, the caribou exhibited no obvi-ous signs of nervousness and continued feeding as the bearapproached. Many of the caribou were facing away fromthe bear.The bear was within 20 m of the caribou herd when itbroke out of the willows and ran toward the nearestindividuals. The herd immediately began running away.Most of the caribou fanned out in an easterly direction, buttwo individuals moved south. The bear then turned towardand chased the two caribou that had separated from theherd, but did not get closer than 10 m. After only about 20seconds of running, the bear slowed to a walk but contin-ued moving toward the herd, which by then had dispersedsomewhat. The herd had also slowed to a walk, but contin-ued to move away from the bear. At this time the two lonecaribou rejoined the herd. The group continued walkingnortheast and resumed grazing.After ~45 seconds of walking toward the herd, the bearcharged toward the herd again from ~40 m away. The bearcontinued chasing the herd for ~90 seconds and thenstopped. The caribou herd continued moving slowly northand began grazing shortly after the chase ended. The bearremained within 500 m of the herd for 45 additionalminutes, but was not observed stalking or chasing againthat day.On 17 July 1998, a subadult bear was observed movingslowly toward a group of caribou. It is unknown if this wasthe same bear observed on the previous day. Again, thewind was blowing from the north-northwest. The bearemerged from the willows on the edge of a small lake andmoved west toward a small group of caribou that wasmoving slowly along an open beach ridge. On this occa-sion, the caribou stopped grazing when the bear was 100 maway and began running to the south almost immediately.The bear did not run after the caribou.On four additional occasions during the summers of1998 and 1999, we observed polar bears within 100 m ofcaribou, but no other chasing behaviour was observed. Apolar bear was observed feeding on a caribou calf carcasson 15 July 1998, but the cause of the calf’s death wasunknown. Polar bears are adept scavengers, so it is impos-sible to tell if the bear killed the calf or if it was alreadydead when found.DISCUSSIONThe behaviour we observed was similar to the behav-iour of polar bears hunting seals (Stirling, 1974) andwillow ptarmigan (Miller and Woolridge, 1983). There-fore, we interpret the behaviour as a predation attempt.A bear would realize a nutritional benefit from a suc-cessful caribou hunt during the summer months. However,there is a significant energetic cost involved in chasingcaribou. Caribou are generally highly vigilant animals,and they are well adapted to travelling at high speeds tooutrun predators such as wolves (Canis lupus). Thus, thelikelihood of a polar bear capturing a healthy, adult cari-bou is presumably low. Furthermore, polar bears are sus-ceptible to hyperthermia during almost any bout of exercise,especially during warm weather (Best, 1982).Lunn and Stirling (1985) predicted that because of thehigh cost of running, a bear chasing snow geese would notreceive a net gain in energy unless it caught a goose within12 seconds. Similarly, chasing caribou would likely pro-duce a benefit only over short distances. Lions (Felis leo),which are also inefficient runners, are ambush predatorsthat normally chase prey only for short distances (Schaller,1974; Taylor, 1976; Stirling, 1988). Both vegetation coverand wind direction greatly influence the success of lions incapturing ungulates (Schaller, 1974). In our first observa-tion, the polar bear appeared to be using the tall willowsand wind direction to move close to the caribou. In thesecond observation, without the benefit of wind directionand cover, the bear was not able to get as close to thecaribou before being detected and avoided.The attempts that we observed could have been unsuc-cessful because there were no unhealthy individuals oryoung in the groups chased. It is also possible that theyoung bear in this case was simply testing potential prey.Alternatively, subadults may need to further supplementtheir diet during the summer months to reduce weight loss,as they tend to be less successful at hunting and protectingtheir kills on the sea ice (Derocher and Stirling, 1990).Finally, while the current observations strongly suggestpredatory behaviour, we cannot rule out other possibleexplanations, such as play. However, play is an integralpart of developing predatory skills (Fagen, 1976; Martinand Caro, 1985), so predatory and play behaviours are notnecessarily mutually exclusive.Polar bears return annually to Wapusk National Parkduring the ice-free period of Hudson Bay (usually fromJuly to November). They use the coastal area, whichprovides a cooling breeze off Hudson Bay and a potentialsource of beached marine mammals (Derocher and Stir-ling, 1990). During the calving and post-calving period(May to September), the Cape Churchill caribou popula-tion (approximately 4000 individuals) remains in thiscoastal area for insect avoidance and to access graminoidand shrub vegetation (Campbell, 1996). As a result, polarbears and caribou are together at high densities in this areafor up to three months each year, a situation in whichinteractions between them could occur frequently.ACKNOWLEDGEMENTSThese observations were made while conducting researchsupported by Wapusk National Park, the Manitoba Department ofConservation, the Churchill Northern Studies Centre, the NorthernPOLAR BEAR PREDATORY BEHAVIOUR • 195Studies Training Program of the Department of Indian and NorthernAffairs Canada, the Canadian Department of Fisheries and Oceans,the Western Canada Service Centre of Parks Canada, Wat’cheeLodge, the Canadian Wildlife Federation, and the Manitoba Chapterof the Wildlife Society. F. Miller and I. Stirling provided valuablepersonal communications from their extensive experiences in thefield. We also appreciate the ongoing support of N. Kenkel and S.McLachlan. Special thanks to C. Hagen, N. Kenkel, J. Hare, D.Clark, I. Stirling, A. Derocher, and three anonymous reviewers fortheir valuable comments and discussion.REFERENCESABRAHAM, K.F., MINEAU, P., and COOKE, F. 1977. Unusualpredators of snow goose eggs. Canadian Field-Naturalist 91:317 –318.BEST, R.C. 1982. Thermoregulation in resting and active polarbears. Journal of Comparative Physiology 146:63 –73.BOERTJE, R.D., GASAWAY, W.C., GRANGAARD, D.V., andKELLYHOUSE, D.G. 1988. Predation on moose and caribou byradio-collared grizzly bears in east central Alaska. CanadianJournal of Zoology 65:1597 –1606.CAMPBELL, M. 1996. The winter ecology of Cape Churchillcaribou (Rangifer tarandus sp.). MSc. Thesis, University ofManitoba, Winnipeg. 216 p.CASE, R., and STEVENSON, J. 1991. Observation of barren-ground grizzly bear, Ursus arctos, predation on muskoxen,Ovibos moschatus, in the Northwest Territories. Canadian Field-Naturalist 105:105 –106.CLARKSON, P.L., and LIEPINS, I.S. 1993. Grizzly bear, Ursusarctos, predation on muskox, Ovibos moschatus, calves near theHorton River, Northwest Territories. Canadian Field-Naturalist107:100 –102.DEROCHER, A.E., and STIRLING, I. 1990. Distribution of polarbears, Ursus maritimus, during the ice-free period in westernHudson Bay. Canadian Journal of Zoology 68:1395 –1403.DEROCHER, A.E., WIIG, Ø., and BANGJORD, G. 2000. Predationof Svalbard reindeer by polar bears. Polar Biology 23:675 –678.DONALDSON, G.M., CHAPDELAINE, G., and ANDREWS,J.D. 1995. Predation of thick-billed murres, Uria lomvia, at twobreeding colonies by polar bears, Ursus maritimus, and walruses,Odobenus rosmarus. Canadian Field-Naturalist 109:112 –114.FAGEN, R. 1976. Exercise, play and physical training in animals.Perspectives in Ethology 2:189 – 219.GUNN, A., and MILLER, F.L. 1982. Muskox bull killed by abarren-ground grizzly bear, Thelon Game Sanctuary, NWT.Arctic 35:545 –546.HOBSON, K.A., and STIRLING, I. 1997. Low variation in bloodδ13 C among Hudson Bay polar bears: Implications for metabolismand tracing terrestrial foraging. Marine Mammal Science 13:359 –367.KNUDSEN, B. 1978. Time budgets of polar bears, Ursus maritimus,on North Twin Island, James Bay, during summer. CanadianJournal of Zoology 56:1627 –1628.KURTÉN, B. 1964. The evolution of the polar bear, Ursus maritimusPhipps. Acta Zoologica Fennici 108:1 –30.LOWRY, L.F., BURNS, J.J., and NELSON, R.R. 1987. Polar bear,Ursus maritimus, predation on belugas, Delphinapterus leucas,in the Bering and Chukchi Seas. Canadian Field-Naturalist101:141 –146.LUNN, N.J., and STIRLING, I. 1985. The significance ofsupplemental food to polar bears during the ice-free period ofHudson Bay. Canadian Journal of Zoology 63:2291 –2297.MARTIN, P., and CARO, T.M. 1985. On the functions of play andits role in behavioural development. Advances in the Study ofBehaviour 15:59 –103.MILLER, G.D., and WOOLRIDGE, D.R. 1983. Small game huntingbehaviour of polar bears, Ursus maritimus. Canadian Field-Naturalist 97:93 –94.OVSYANIKOV, N.G. 1996. Interactions of polar bears with otherlarge mammals, including man. Journal of Wildlife Research1:254 –259.RAMSAY, M.A., and HOBSON, K.A. 1991. Polar bears makelittle use of terrestrial food webs: Evidence from stable-carbonisotope analysis. Oecologia 86:598 – 600.RAMSAY, M.A., NELSON, R.A., and STIRLING, I. 1991. Seasonalchanges in the ratio of serum urea to creatinine in feeding andfasting polar bears. Canadian Journal of Zoology 69:298 –302.RUGH, D.J., and SHELDEN, K.E.W. 1993. Polar bears, Ursusmaritimus, feeding on beluga whales, Delphinapterus leucas.Canadian Field-Naturalist 107:235 –237.RUSSELL, R.H. 1975. The food habits of polar bears of James Bayand southwest Hudson Bay in summer and autumn. Arctic28:117 –129.SCHALLER, G.B. 1974. The Serengeti lion: A study of predator-prey relations. Chicago: University of Chicago Press.SMITH, A.E., and HILL, M.R.J. 1996. Polar bear, Ursus maritimus,depredation of Canada goose, Branta canadensis, nests. CanadianField-Naturalist 110:339 – 340.SMITH, T.G. 1980. Polar bear predation of ringed and beardedseals in the land-fast sea ice habitat. Canadian Journal of Zoology58:2201 –2209.SMITH, T.G., and SJARE, B. 1990. Predation of belugas andnarwhals by polar bears in nearshore areas of the Canadian HighArctic. Arctic 43:99 –102.STEMPNIEWICZ, L. 1993. The polar bear, Ursus maritimus,feeding in a seabird colony in Frans Josef Land. Polar Research12:33 –36.STIRLING, I. 1974. Midsummer observations on the behaviour ofwild polar bears, Ursus maritimus. Canadian Journal of Zoology52:1191 –1198.———. 1988. Polar bears. Ann Arbor: University of Michigan Press.STIRLING, I., and ARCHIBALD, W.R. 1977. Aspects of predationof seals by polar bears. Journal of the Fisheries Research Boardof Canada 34:1126 –1129.STIRLING, I., and ØRITSLAND, N.A. 1995. Relationshipsbetween estimates of ringed seal (Phoca hispida) and polarbear (Ursus maritimus) populations in the Canadian Arctic.Canadian Journal of Fisheries and Aquatic Sciences 52:2594 – 2612.STIRLING, I., LUNN, N.J., and IACOZZA, J. 1999. Long-termtrends in the population ecology of polar bears in westernHudson Bay in relation to climatic change. Arctic 52:294 –306.196 • R.K. BROOK and E.S. RICHARDSONTAYLOR, R.J. 1976. Value of clumping to prey and the evolutionaryresponse of ambush predators. The American Naturalist 110:13 –29.WATTS, P.D., and HANSEN, S.E. 1987. Cyclic starvation as areproductive strategy in the polar bear. Symposia of the ZoologicalSociety of London 57:305 –318.YOUNG, D.D., and McCABE, T.R. 1997. Grizzly bear predationrates on caribou calves in northeastern Alaska. Journal of WildlifeManagement 61:1056 –1066.

Observations of Polar Bear Predatory Behaviour toward Caribou

in western Hudson Bay. Before chasing the caribou, the polar bear appeared to make use of wind direction and vegetation cover in order to move close to them. While there have been very few documented cases of the two species interacting, our observations indicate that polar bears will stalk and chase caribou

Ryan K. Brook

Evan S. Richardson

CiteSeerX

Observations of polar bear predatory behaviour toward caribou. Arctic 55(2

https://journalhosting.ucalgary.ca/index.php/arctic/article/download/63760/47695

Observations of Polar Bear Predatory Behaviour toward Caribou

Abstract

Similar works

Full text

Available Versions

University of Calgary Journal Hosting

CiteSeerX