some event (e.g., extremely deep or shallow snow) changes
moose or caribou vulnerability to predation (Mech et al.
1998), or if the age or sex structure of a moose population
changes with time, affecting fecundity or vulnerability to
predation (Van Ballenberghe and Ballard 1997). A density-
independent response can strongly influence prey selection
and wolf functional responses (Huggard 1993; Mech et al.
1995), and other factors besides prey density should be mea-
sured when assessing wolf predation rates.
Data quality
Several factors could have confounded our estimates of
kill rate. Caribou are available to more than half of the packs
in summer and fall, but to fewer packs in late winter. By
studying wolves in late winter we probably underestimated
predation on caribou and overestimated predation on moose.
We studied kill rates when moose were increasing from low
to moderate densities (0.26–0.44/km
2
). Kill rates cannot be
expected to remain the same at lower moose densities
(Messier 1994; Hayes and Harestad 2000b) in areas where
relative densities of moose and caribou differ (Dale et al.
1995) or where other factors such as snow depth influence
prey vulnerability (Mech et al. 1995). Our method of deter-
mining winter predation rates did not account for any spatial
differences in moose in late winter, which we knew existed
among wolf-pack territories (R. Florkiewicz, Yukon Fish and
Wildlife Branch, Box 2703, Whitehorse, YT Y1A 2C6, Can-
ada, unpublished data).
Acknowledgements
The Yukon Fish and Wildlife Branch provided generous
financial and logistic support for this study. Field staff
who assisted us in the study include P. Maltais, P. Koser,
C. Promberger, P. Kaczensky, R. Florkiewicz, D. Bakica,
D. Anderson, and D. Thiel. D. Denison, T. Hudgin, and
D. Drinnan flew fixed-wing aircraft with great skill and inter-
est. Helicopter pilots J. Witham and J. Henderson made wolf-
capture flights seem easy. All pilots were invaluable members
of the study team. G. Sharam, M. Oakley, F.L. Bunnell,
E. Cooch, and R. Ydenberg made positive criticisms of the
manuscript. We also thank Dr. A. Angerbjorn and an anony-
mous reviewer for improving the paper. We especially thank
B. Gasaway for his friendship and valuable insights in wolf–
prey systems and for his constructive advice on the manu-
script before his untimely death.
References
Ackerman, B.B., Leban, F.A., Garton, E.O., and Samuel, M.D.
1990. User’s manual for program
HOME RANGE
. 2nd ed. Tech.
Rep. No. 15, Forest, Wildlife, and Range Experiment Station,
University of Idaho, Moscow.
Ballard, W.B., and Van Ballenberghe, V. 1997. Predator/prey rela-
tionships. In Ecology and management of the North American
moose. Edited by A.W. Franzmann and C.C. Schwartz. Smithso-
nian Institute Press, Washington, D.C. pp. 247–273.
Ballard, W.B., Whitman, J.S., and Gardner, C.L. 1987. Ecology of
an exploited wolf population in south-central Alaska. Wildl.
Monogr. No. 98.
Bertram, B.C.R. 1978. Living in groups: predators and prey. In Be-
havioural ecology: an evolutionary approach. Edited by J.R.
Krebs and N.B. Davies. Sinauer Associates Inc., Sunderland,
Mass. pp. 64–96.
Boutin, S. 1992. Predation and moose population dynamics: a cri-
tique. J. Wildl. Manage. 56: 116–117.
Cooper, S.M. 1991. Optimal hunting group size: the need for lions
to defend their kills against loss to spotted hyenas. Afr. J. Ecol.
29: 130–136.
Dale, B., Adams, L.G., and Boyer, R.T. 1994. Functional response
of wolves preying on barren-ground caribou in a multiple prey
ecosystem. J. Anim. Ecol. 63: 644–652.
Dale, B.W., Adams, L.G., Boyer, R.T. 1995. Winter wolf predation
in a multiple ungulate prey system, Gates of the Arctic National
Park, Alaska. In Ecology and conservation of wolves in a chang-
ing world. Edited by L.N. Carbyn, S.H. Fritts, and D.R. Seip.
© 2000 NRC Canada
56
Can. J. Zool. Vol. 78, 2000
Pack size
No. of
wolves
No. of
packs
Mean no. of
moose killed in
winter per pack
Total no. of
moose killed
in winter
Model 1
2
34
17
27
459
6
36
6
35
210
10
30
3
46
138
Total
26
807
Model 2
2
10
5
27
135
6
30
5
35
175
10
60
6
46
276
Total
16
586
Model 3
2
20
10
27
270
6
30
5
35
175
10
50
5
46
230
Total
20
675
Table 4. Three hypothetical models of predation rates by 100 wolves on moose in winter,
depending on differences in pack-size frequency.
J:\cjz\cjz78\cjz-01\Z99-187.vp
Friday, February 25, 2000 9:27:40 AM
Color profile: Disabled
Composite Default screen
Canadian Circumpolar Institute, University of Alberta, Edmon-
ton. pp. 223–230.
Farnell, R., and MacDonald, J. 1988. The demography of Yukon’s
Finlayson caribou herd, 1982–1987. Yukon Fish and Wildlife
Branch Rep., Whitehorse.
Franzmann, A.W., LeResche, R.E., Rausch, R.A., and Oldemeyer,
J.L. 1978. Alaska moose measurements and weights and
measurement–weight relationships. Can. J. Zool. 56: 298–306.
Fuller, T.K. 1991. Effect of snow depth on wolf activity and prey
selection in north central Minnesota. Can. J. Zool. 69: 283–287.
Gasaway, W.C., Stephenson, R.O., Davis, J.L., Shepherd, P.E.K.,
and Burris, O.E. 1983. Interrelationships of wolves, prey, and
man in interior Alaska. Wildl. Monogr. No. 84.
Gasaway, W.C., Boertje, R.D., Grangaard, D.V., Kelleyhouse,
D.G., Stephenson, R.O., and Larsen, D.G. 1992. The role of pre-
dation in limiting moose at low densities in Alaska and Yukon
and implications for conservation. Wildl. Monogr. No. 120.
Gauthier, D., and Theberge, J. 1985. Wolf predation in the Burwash
caribou herd, southwest Yukon. Rangifer Spec. Issue No. 1.
pp. 137–144.
Harrison, S. 1990. Cougar predation on bighorn sheep in the Junc-
tion wildlife management area, British Columbia. M.Sc. thesis,
University of British Columbia, Vancouver.
Hatter, I.W., and Bergerud, W.A. 1991. Moose recruitment, adult
mortality, and rate of change. Alces, 27: 65–73.
Haugen, H.S. 1987. Den-site behavior, summer diet, and skull inju-
ries of wolves in Alaska. M.Sc. thesis, University of Alaska,
Fairbanks.
Hayes, R.D., and Harestad, A.S. 2000a. Demography of a recover-
ing wolf population in the Yukon. Can. J. Zool. 78: 36–48.
Hayes, R.D., and Harestad, A.S. 2000b. Wolf functional response
and regulation of moose in the Yukon. Can. J. Zool. 78: 60–66.
Hayes, R.D., Baer, A.M., and Larsen, D.G. 1991. Population dy-
namics and prey relationships of an exploited and recovering
wolf population in the southern Yukon. Yukon Fish and Wildlife
Branch Rep. TR 91-1, Whitehorse.
Heinrich, B. 1991. Ravens in winter. Vintage Books, New York.
Huggard, D.J. 1993. Effect of snow depth on predation and scav-
enging by gray wolves. J. Wildl. Manage. 57: 382–388.
J
drzejewski, W., Jdrzejewska, B., Okarma, K., and Ruprecht, A.L.
1992. Wolf predation and snow cover as mortality factors in the
community of the Bialowieza National Park, Poland. Oecologia,
90: 27–36.
Jingfors, K. 1988. Moose population characteristics in the North
Canol and Frances Lake areas, November 1987. Yukon Fish and
Wildlife Branch Rep., Whitehorse.
Krebs, C.J., Boutin, S., Boonstra, R., Sinclair, A.R.E., Smith,
J.N.M., Dale, M.R.T., Martin, K., and Turkington, R. 1995. Im-
pact of food and predation on the snowshoe hare cycle. Science
(Washington, D.C.), 269: 1112–1115.
Larsen, D.G., and Ward, R.M.P. 1995. Moose population character-
istics in the Frances Lake and North Canol areas. Yukon Fish
and Wildlife Branch Rep. PR 95-1, Whitehorse.
Larsen, D.G., Gauthier, D.A., and Markel, R. 1989. Causes and rates
of moose mortality in the southwest Yukon. J. Wildl. Manage.
53: 548–557.
Mech, L.D. 1974. Current techniques in the study of elusive wil-
derness carnivores. In Proceedings of 11th Congress of the In-
ternational Union of Game Biologists, Stockholm, Sweden, 3–7
September 1973. Edited by I. Kjerner and P. Bjurholm. Swedish
National Environment Protection Board, Stockholm. pp. 315–
322.
Mech, L.D., and Karns, P.D. 1977. Role of the wolf in a deer de-
cline in the Superior National Forest. U.S. For. Serv. Res. Rep.
NC-148.
Mech, L.D., Meier, T.J., Burch, J.W., and Adams, L.G. 1995. Pat-
terns of prey selection by wolves in Denali National Park,
Alaska. In Ecology and conservation of wolves in a changing
world. Edited by L.N. Carbyn, S.H. Fritts, and D.R. Seip. Cana-
dian Circumpolar Institute, University of Alberta, Edmonton.
pp. 231–243.
Mech, L.D., Adams, L.G., Meier, T.J., Burch, J.W., and Dale, B.W.
1998. The wolves of Denali. University of Minnesota Press,
Minneapolis.
Messier, F. 1991. The significance of limiting and regulating fac-
tors on the demography of moose and white-tailed deer. J.
Anim. Ecol. 60: 377–393.
Messier, F. 1994. Ungulate population models with predation: a
case study with North American moose. Ecology, 75: 478–488.
Messier, F., and Crête, M. 1985. Moose–wolf dynamics and the
natural regulation of moose populations. Oecologia, 65: 503–
512.
Neiland, K.A. 1970. Weight of dried marrow as indicator of fat in
caribou femurs. J. Wildl. Manage.
34: 904–907.
Nudds, T.D. 1978. Convergence of group size strategies by mam-
malian social carnivores. Am. Nat. 112: 957–960.
Packer, C., and Ruttan, L. 1988. The evolution of cooperative hunt-
ing. Am. Nat. 132: 159–198.
Packer, C., Scheel, D., and Pusey, A.E. 1990. Why lions form
groups: food is not enough. Am. Nat. 136: 1–19.
Peterson, R.O. 1977. Wolf ecology and prey relationships on Isle
Royale. U.S. Natl. Park Serv. Sci. Monogr. Ser. 11.
Peterson, R.O., and Page, R.E. 1983. Cyclic fluctuations of wolves
and moose at Isle Royale National Park, U.S.A. Acta Zool.
Fenn. 174: 252–254.
Peterson, R.O., Allen, D.L., and Dietz, J.M. 1982. Depletion of
bone marrow fat in moose and a correction for dehydration. J.
Wildl. Manage. 46: 547–551.
Peterson, R.O., Woolington, J.D., and Bailey, T.N. 1984. Wolves of
the Kenai Peninsula. Alaska. Wildl. Monogr. No. 88.
Promberger, C. 1992. Wölfe und Scavenger. [Wolves and scaven-
gers.] [With English abstract.] Diplomarbeit, Ludwig Maximil-
lians Universität, München, Germany.
Rodman, P.S. 1981. Inclusive fitness and group size with a recon-
sideration of group sizes in lions and wolves. Am. Nat. 118:
275–283.
Schmidt, P.A., and Mech, L.D. 1997. Wolf pack size and food ac-
quisition. Am. Nat. 150: 513–517.
Schwartz, C.C., Regelin, W.L., and Franzmann, A.W. 1987. Sea-
sonal weight dynamics of moose. Swedish Wildl. Res. Suppl.
No. 1. pp. 301–310.
Seip, D.R. 1991a. Predation and caribou populations. Rangifer
Spec. Issue No. 7. pp. 46–52.
Seip, D.R. 1991b. Wolf predation, wolf control and the manage-
ment of ungulate populations. In Wildlife 2001: populations.
Edited by D.R.J. McCullough and R.H. Barrett. Elsevier Ap-
plied Science, New York. pp. 331–340.
Seip, D.R. 1992. Factors limiting woodland caribou populations
and their interrelationships with wolves and moose in southeast-
ern British Columbia. Can. J. Zool. 70: 1494–1503.
Sergent, D.E., and Pimlott, D.H. 1959. Age determination in
moose from sectioned incisor teeth. J. Wildl. Manage. 23: 315–
321.
Skoog, R.O. 1968. Ecology of the caribou (
Rangifer tarandus granti)
in Alaska. Ph.D. thesis, University of California, Berkeley.
© 2000 NRC Canada
Hayes et al.
57
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