AgricultureU:i::dSJ:t_):,. Wolf Populationin the C nt.ra/

sFNo_tr__tnCEexptrra/ent up rior NationalResearchPaper NC,270

N Forest, 1967-198' _'/ L. DavidMech

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Mech, L. David.Wolf population in the central Superior National Forest, 1967-1985.

Res. Pap. NC-270. St. Paul, MN: U.S. Department of Agriculture,Forest Service, North Central Forest Experiment Station; 1986. 6 p.

Aerial radio-tracking and observation showed total number ofwolves per year in 2,060-kin 2area varied from 35 to 87 _n winter andfrom 30 to 78 in spring and generally declined because of a decreasingdeer herd. Since winter 1977-1978, the population has remained rela-tively stable because an increasing proportion of it has switched topreying on moose. The number of wolves preying on deer has contin-ued to decline.

KEY WORDS: Deer, moose, territoriality, home range, radio-• tracking, telemetry, predator, prey, Minnesota.

North Central Forest Experiment StationForest Service--U.S. Department of Agriculture

1992 Folwell AvenueSt Paul, Minnesota 55108

Manuscript approved for publication February 6, 1986' 1986

WOLF POPULATION IN THE CENTRAL SUPERIORNATIONAl. FOREST, 1967-1985°

..

- L. David Mech,Wildlife Research Biologist,.

Patuxent' Wildlife Research Center,U.S. Fish and Wildlife Service

..

Large carnivores are long-lived. Wolves (Canis lu- with the following species present: jack pine (Pinuspus), f0rexample, can livesome 16years in captivity banksiana Lamb.), white pine (P. strobus L.), red(Young 1944) and at least 13 years in the wild (Mech pine (P. resinosa), black spruce (Picea mariana1981). Thus acomplete understanding of their ecol- (Mill.) B.S.P.), white spruce (P. glauca (Moench)ogy and population dynamics requires long-term in- Voss), balsam fir (Abies balsamea (L.) Mill.), whitevestigations. The longest study of wolf numbers has cedar (Thuja occid, ntalis L. ), and tamarack (Lar/xbeen conducted in Isle Royale National Park, Lake /ar/cina (DuRoi) K. Koch). However, as a result ofSuperior, where wolves have been censused annu- extensive cutting and fires much of the conifer coverally since 1959 (Mech 1966, Jordan et al. 1967, is interspersed with large stands of white birch (Be-Peterson 1977, Peterson et al. 1984). That study has tu/a papyrifera Marsh.) and aspen (Populus tremu-yielded several new insights into wolf and prey rela- /o/des Michx.). Detailed descriptions of the foresttionships (Allen 1979, Peterson et al. 1984). How- vegetation were presented by Ohm_nn and Reamever, Isle Royale is a 544-km 2 island with the wolves (1969).

living on a moose (Alces alces) economy. Thus it is In the northeastern half of this study area, as welluseful to study wolf.numbers in a larger, mainlandecosystem with a more complex prey base. as in the region imm_ediately north and east of it, the _

In 1966 such an investigation was begun in thecentral Superior National Forest of northeastern o.tn /Minnesota. This area had the added advantage of /background data from other studies (Olson 1938, ..........._-............

Stenlund 1955). Earlier results of the present study ihave been reported (Mech 1973, 1977), but the _ lO ...present document summarizes the data from 1967 ....." s ...'•. /through 1985. my• _..._ _

STUDY //""''---/, /. . .....The present study area encompasses some 2,060

kin_2 immediately east of Ely in the east-central Su- ... jperior National Forest (48°N, 92°W). Although I

somewhat smaller than the areas reported on ear- ".... :eKe: !lier, this Study area encompasses the core of that ,_l_region in which I have been able to monitor the wolfpopulation .during the entire 19-year period (fig. 1).

The area represents approximately 3 percent of the Figure 1.--Wolf census area (2060 km 2 in the centraltotal wolf range in Minnesota. Superior National Forest of northeastern Minne-

The topography varies from large stretches of sota. Outlined, numbered areas represent mini-swamps torocky ridges, with altitudes ranging from mum wolf pack territory boundaries for winter325 to700 meters above sea level. Winter tempera- 1984-1985 as follow: 1, Ensign L. Pack; 2, Pagamitures lower than -35°C are not unusual, and snow Pack No. 2; 3, Wood L. Pack; 4, Birch L. Pack; 5,depths (usually from about mid-November through Little Gabbro Pack; 6, Jackpine Peek No. 4; 7, Saw-about mid-April) generally range from 50 to 75 cm bill Pack; 8, Quadga L. Pack No. 2;"9. Maniwaki L.on the!evel. Summer temperatures rarely exceed Pack No. 2; 10, Malberg L. Pack (approximate terri-+35°C. Conifers predominate in the forest overstory, tory because packwas not radioed in 1984-85).

r |

overwintering population of white-tailed deer (Odo- and later year's data for radioed packs occupyingcoileus virginianus) were depleted about 1975 by a those territories. Data from before 1968 were basedcombination of a series of severe winters, maturing solely on observations of nonradioed packs duringvegetation, and high wolf numbers (Mech and Karns intensive aerial observation of the area.

1977). Mooseinhahit the entire study area but occur In this estimate of wolf population trend, the hum-at a higher density in the northeastern half (Peek etal. 1976). In spring, some 32 percent of the deer ber of lone wolves was considered inconsequentialinhabiting the southwestern half of the study area because their proportion of the population was low.migrate into the northeastern half Or beyond and During the earlier part of the present study, 10nereturn in fall (Hoskinson and Mech 1976, Nelson wolves were estimated at 7-14 percent of the popula-

tion (Mech 1973), and loners comprised 16 percent ofand Mech 1981, 1986). Beaver (Castor canadensis)282 wolves captured in and around the present study

are available throughout the study area, but gener-area (Mech unpublished).ally only from about April through November be-

cause of ice during the rest of the year. Although all Some data pertaining to individual pack years inthree prey species are consumed, by wolves in the the present article may differ from data presentedre.on (Frenze] 1974), Since about 1975 the primary previously (Mech 1973, 1977) because of reinterpre-prey of wolves inhabiting the northeastern half has tation of the data based on additional experienceeen moose, whereas those in the southwestern half with these packs. Furthermore the wolf population

have consumed primarily deer (Mech, unpublished), trend may also vary slightly from previous publica-• tions because of the difference in the preciseYear-around hunting and trapping of wolves was boundaries of the study areas considered. Neverthe-

legal until October 1970 when they were fully pro-te_ on federal land Within the Superior National less, tlze earlier results remain basically the same inForest by the U.S. Forest Service. In August 1974, the present study.wolves were protected by the Endangered Species

Act of 1973. In 1978, the wolf in Minnesota was RESULTSreclassified from endangered to threatened but re-

mains legally protected except when taken by U.S. Some 250 wolves representing up to 13 packs inFish.& Wildlife Service agents reacting to depreda- this study area were radio-tagged and studied fromtions on livestock outside the present study area. 1968 through 1985 (table 1). The number of radioedHowever, in parts of the study area adjacent to towns packs in the study area each winter and spring(fig. 1), moderate illegal taking continues, primarily ranged from 1 to 8. Each radioed wolf was located anin fall and winter (Mech 1977, and unpublished), average of approximately 38 times per year, and

they and their pack members were observed an aver-

METHODS age of approximately 18 times per year. Pack sizesvaried from 2 to 15 during winter and from 2 to 11

• The primary technique used in this investigation during spring. Some packs disappeared as deter-mined by the individual histories of radioed mem-

hasbeen live-trapping wolves, outfitting each with a bets of those packs (Mec]i unpublished). Sometimesradi0-collar, _aerially radio-tracking them at least their places were taken by new colonizing packs

•Once per week from April through November and at• • least twice per week from December through March, which may or may not have settled in precisely the

same territories. A pack occupying a general areaand aerially observing and counting them as often as inhabited earlier by a radioed pack was usuallypossible, primarily from December through April listed under the same name (table 1) even though(Mech 1974): The maximum number of wolves seenin each pack during December through February is continuity via overlapping radio tenures was not al-considered the winter pack size, and the maximum ways documented.seen in each pack in March and April represents the Generally the wolf population increased each yearspring pack size (Mech 1973). up to 86 percent from spring to winter as a result of

Pack territories based on.radio locations were de- reproduction, although during two summers wolflineated for each radioed pack in the study area each numbers actually decreased (table 2). From winteryear, The existence of nonradioed packs in the Study to spring the population decreased as much asarea in any year were inferred from voids in the 40 percent per winter as a result of mortality (Mechmaps ofthe territorial mosaic. Incidental observa- 1977) and dispersal (Mech in press).tions ofnonradioed packs in these voids were used to The total number of wolves in the census area inrepresent sizes of these nonradioed packs. If such winter varied.from 35 to 87 and in spring, from 30 todata were unavailable in a given year, pack-size es- 78 over the 19-year period, and generally declined_imates were made subjectively based on previous (fig. 2). However, about 1978 wolves began recoloniz-

2

Table 2.--Wolf population changes in the central Superior National Forest, based On data from table 1

PorcentchangeInwolfnumbersm• Percentchangeintotalnumbersinstudyarea deereconomyInstudyarea

Winterto Springto Winterto _d_ to Wintwto Mmr to IkNriqtoYear spring nextwinter wintw spnng spdng mS_rl__ln_ winter1967-1968 - - +4 - - - +4 -

1969 - - +11 - - - +11 --1970. - - +6 - - - +6 -1971' -7 +5 -3 - -7 +5 -3 -1972 -27 +17 -2 -23 -27 +17 -2 -231973 .. -40 +55 -15 -30 -40 +55 -15 -301974 -35 +5 -7 O0 -35 +5 -7 O01975 -14 +47 -32 -10 -14 +47 -32 -10.1976 ,-14 -6 +27 +26 -14 -6 +27 +281977 -27 +52 -20 -3! -27 +45 -20 -311978 .-26 " +24 +11 +12 -29 +15 +7 +31979 -24 +54 -8 -5 -26 +62 -19 -151980 -19 +9 . +17 +26 -19 +8 +21 +311981 -15 +15 -11 -7 -15 +3 -13 -81982 -6 +14 -2 +7 -8 +15 -12 -61983 " -26 -5 +6 -16 -32 -12 +6 -211984 -14 +80 -30 -19 -13 +50 -39 -231985 -20 - +54 +43 -27 - +30 +10

qnsuflidentdataavailablebeforeSislimebecausepackswerenotradioed.

ing the northeastern part of the study area in which The fate of the other mx members of the originaloverwintering deer and deer.killing wolves were Ms]berg L. Pack is unknown, except that pups werethen absent(Mech and Karns,1977). The newly colo- produced in the north end of the territory, so thenizing Malberg L. Pack increased to 12 members by pack probably persisted.

1983, preyed exclusively on moose during winter, Meanwhile by winter 1984-1985, a pack of fiveand occupied some 20 percent of the study area. including pups, was colonizing the southwestern 20

In spring 1984, four members of the Malberg L. percent of the 1983-1984 Malberg L. Pack territoryPack, including radioed 2-year-old wolf 6417, appar- and expanding southwestward (Quadga Lake Pack).ently split from the remainder of the pack and colo- In addition, the Ensign L. Pack, radioed in springnized the southeastern half of the previous winter's 1984, numbered seven animals by winter 1984-1985,territory, expanded southeastward, and increased to and preyed primarily on moose. The last time a pack

; seven; this pack was renamed '_Ianiwaki L. Pack" in that area had been radio-tagged (winter 1979-because it occupied the territory of the former Mani- 1980) they had migrated out of their territory duringwaki L. Pack which had died out the previous year. winter and preyed on deer several miles westward.

The result of the wolf population's partial switch

_. - to a moose economy from 1978 through 1985 was to

" allow the total .population of the study area to re-"_ main relatively stable during that period (fig. 2).

Meanwhile, the number Ofdeer-killing wolves in thestudy area continued to decline, although both this

t: so subpopulation and the entire population of the study_ area increased from 1984 to 1985 (fig. 2).

m \..,V DISCUSSION AND CONCLUSION

o , , .... ....• The wolf population decline in this study area re-

Figure 2.--Wolf population trend in the central Su- suited from a decrease in the wows main prey, theperior National Forest during winter. Solid line in- white-tailed deer (Mech and Karns 1977). The deerdicates total population in the 2,060-km _ study decline ended about 1977, and since then the popula-area. About 1976-1977, part of the population be- tion has remained low although relatively stablegan preying primarily on moose during winter. The (Nelson and Mech 1986). Nevertheless the wolf popdottedline represents the trend in number of wolves ulation on a deer economy continued to decline forcontinuing to prey on deer. several more years (fig. 2). This fact seems to indi-

4

cate that at low deer numbers wolves are unable to provals, permits, and miscellaneous support and en-kill enough deer to enable the wolves to maintain couragement. G. DelGiudice, L. Rogers, andtheir numbers. Further evidence is found in the T. Fuller offered helpful suggestions to improve theswi'tching of part of the wolf population to a moose manuscript.economy which allowed the wolf population to stabi-lize in the study area at a density of about 2.3 per100 km 2 for several years (fig. 2). LITERATURE CITED

It is unknown whether the wolves colonizing the Allen, D. L. Wolves of Minong. Boston: Houghtondeer-free area in 1978 dispersed from packs on a deer

Mifflin Co.; 1979. 499 p.economy and then learned to exploit moose, orwhether they came from a moose-killing population Frenzel, L. D. Occurrence of moose in food of wolvesas revealed by scat analyses: a review of Northto the north. Wolves can disperse distances of at American studies. Naturaliste Can. 101" 467-479;least 866 km (Fritts 1983), but it apparently took 1974.several years for wolves to fill the void in the north-eastern part of the study area (Mech unpublished) Fritts, S. H. Record dispersal by a wolf from Minne-sota. J. Mammal. 64: 166-167; 1983.even though dispersers were available from deer-killing wolves to the west and south (Mech in press). Hoskinson, R. L.; Mech, L. D. White-tailed deer mi-

• gration and its role in wolf predation. J. Wildl.The second alternative seems more likely. Althoughwolves that prey primarily on deer can learn to kill Manage. 40: 429-441; 1976.moose (Mech unpublished), there was no indication Jordan, P. A.; Shelton, P. C.; Allen, D. L. Numbers,turnover, and social structure of the Isle Royalethat this process took place in the northeastern part wolf population. Am. Zool. 7: 233-252; 1967.of the study area. Mech, L. D. The wolves of Isle Royale. Fauna ser. 7.

The wolf population trend in this study area does Washington, DC" U.S. National Park Service,not necessarily apply to surrounding regions or to 1966. 210 p.the remaining 97 percent of Minnesota wolf range. Mech, L. D. Wolf numbers in the Superior NationalBecause the deer decline itself was localized to the Forest of Minnesota. Res. Pap. NC-97. St. Paul,immediate vicinity of the study area (Mech and MN: U.S. Department of Agriculture, Forest Ser-Karns 1977), wolves throughout most of the rest of vice, North Central Forest Experiment Station;their Minnesota range almost certainly were not 1973. 10 p.similarly affected. Mech, L. D. Current techniques in the study of elu-

sive wilderness carnivores. Int. Conf. Game Biol.Switchingof part of the wolf population to a moose Proc. 11: 315-322; 1974.

economy minimized the effects of a drastic deer de- Mech, L. D. Natality, mortality, and populationcline on wolf numbers. Although extreme fluctua- trend of wolves in northeastern Minnesota. J.tions in both wolves and prey can occur in wolf- Mammal. 58: 559-574; 1977.moose systems (Peterson etaI. 1984), the presence of Mech, L. D. A decade of data from a single wolf.the white-tailed deer as an alternate prey in this

Endangered Species Tech. Bull. 6: 4; 1981.study area should help stabilize wolf numbers. Mech, L. D. Age, season, and social aspects of wolf

dispersal from a Minnesota pack. In: Chepko-Sade, B. D.; Halpin, Z., eds. Proceedings, Sympo-

ACKNOWLEDGMENTS sium on patterns of dispersal among mammalsand their effects on the genetic structure of popu -

This study was supported by the USDI Fish & lations; in press.Wildlife Servi'ce, the USDA North Central Forest Mech, L. D.; Karns, P. D. Role of the wolf in a deerExperiment Station, the Mardag Foundation, World decline in the Superior National Forest. Res. Pap.Wildlife Fund and the New York Zoological Society. NC-148. St. Paul, MN: U.S. Department of Agri-Numerous technicians, volunteers, and students as- culture, Forest Service, North Central Forest Ex-sisted with live-trapping, radio-tagging, radio-track- periment Station; 1977. 23 p.ing and observing the wolves,, and many bush pilots Nelson, M. E.; Mech, L. D. Deer social organizationprovided skillf_ flying. The following individuals and wolf predation in northeastern Minnesota.bear special mention: M. E. Nelson, J. Renneberg, Wildl. Monogr. 77; 1981.53 p.S.T. Knick, J. Burch, P. Magie, D. Mahl, Nelson, M. E.; Mech, L. D. Deer population in theJ. Ortmann, Jr., S. Gheen, J. Grummet, D. Glaser, central Superior National Forest, 1967-1985. Res.G. Riley, R. Himes, D. Monson, F. H. Harrington. Pap. NC-271. St. Paul, MN: U.S. Department ofThe USDA Superior National Forest and the Minne- Agriculture, Forest Service, North Central Forestsota Department of Natural Resources granted ap- Experiment Station; 1986. 7 p.

°

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Ohmann, L. F.; Ream, R. R. Vegetation studies inthe BWCA- a brief report on plant communities.Naturalist 20: 20-29; 1969.

Olson, S. F. A study in predatory relationship withparticular reference to the wolf. Sci. Monthly 46:323-336; 1938.

Peek, J. M.; Urich, D. L.; Mackie, R. J. Moose habitatselection and relationship to forest managementin north-eastern Minnesota. Wildl. Monogr. 48:65 p.; 1.976.

Peterson, R. O. Wolf ecology and prey relationshipson Isle Royale. Sci. Monogr. Ser. II. U.S. NationalPark Service; 1977. 210 p.

Peterson, R. O.; Page, R. E.; Dodge, K. M. Wolves,moose, and the allometry of population cycles. Sci-ence 224: !350-1352; 1984.

Steniund, M- H. 1955. A field study of the timberwolf (Canis lupus) on the Superior NationalForest, Minnesota. Tech. Bull. 4. St. Paul, MN:Minnesota Department of Conservation, 1955.55 p.

Young, S. P. The wolves of North America, Part I.Washingtzn, DC: Am. Wildl. Inst.; 1944. 385 p.

f966- 6NORTHCENTRAL

EHPERIIIIENTSTATION,