Figure 1.—The study area showing locations where wolf-killed and hunter-killed deer were taken. Line arbitrarily separates the hunted area from the wilderness area.Figure 1.—The study area showing locations where wolf-killed and hunter-killed deer were taken. Line arbitrarily separates the hunted area from the wilderness area.(Click for larger image.)
The investigation began in February 1966 and continued through March 1969; the basic objective was to examine as many wolf-killed deer as possible and compare their ages, sex, and condition with a large sample of deer from the population at large in the same area. Wolf-kills were examined only during December through March when they could be found from the air. Aircraft ranging in size from an Aeronca Champ to a Cessna 206 were used to fly over frozen lakes at altitudes up to 2,000 feet to locate wolves (fig. 2), wolf tracks, or kills (fig. 3). We often discovered kills by tracking a wolf pack.
Figure 2.—Wolves were located from the air, usually on frozen lakes. (Photo courtesy of L. D. Mech.)Figure 2.—Wolves were located from the air, usually on frozen lakes. (Photo courtesy of L. D. Mech.)
Figure 3.—Wolf-kills were easily spotted from aircraft. (Photo courtesy of L. D. Mech.)Figure 3.—Wolf-kills were easily spotted from aircraft. (Photo courtesy of L. D. Mech.)
During the winter of 1968-69 this method of finding kills was supplemented by radiotracking five wolves and their associates via aircraft (see Mechet al.,p. 1). The latter technique resulted in increased discovery of inland kills.
A deer carcass was judged killed by wolves if the death had been recent, if tracks or other sign indicated that wolves had fed upon it, and if no other possible cause of death was discovered. Carcasses fed on by wolves but not clearly identifiable as kills were labeled "probable" wolf-kills. Although the cause of death of the specimens in this latter category could not be determined with certainty, there was no reason to believe other agents were involved.
In addition to the wolf-kills examined by project personnel, data and lower jaws from deer judged killed by wolves were contributed by other biologists, game wardens, forest rangers, and others whose competence was known. Nevertheless, if certain identification of carcasses as wolf-kills was not possible, the data were relegated to the "probable" wolf-kill category.
Whenever possible, kills discovered from the air were examined on the ground (fig. 4). Often only skeletal parts remained, but soft parts were also examined when available. Femur marrow, heart, lungs, liver, kidneys, reproductive tracts, and omenta were usually inspected in the field for fat, parasites, and abnormalities, and the degree of subcutaneous back fat was also noted. Hoofs and lower legs were checked, and those showing pathological conditions or abnormalities were collected and examined by the Veterinary Diagnostic Laboratory of the University of Minnesota. All lower jaws found were collected, aged, and examined for dental abnormalities and pathological conditions.
Figure 4.—As many wolf-killed deer as possible were examined from the ground. (Photo courtesy of L. D. Mech.)Figure 4.—As many wolf-killed deer as possible were examined from the ground. (Photo courtesy of L. D. Mech.)
In November 1967 and 1968 hunter-check stations were operated on the study area (fig. 5), and deer bagged by hunters were field-checked for age (Severinghaus 1949) and hoof abnormalities. As many lower jaws as possible were collected from field-checked deer and other deer killed in the area for age determination and examination for abnormal dentition.
Figure 5.—Information about hunter-killed deer in the study area was obtained through hunter-check stations. (Photo courtesy of L. D. Frenzel.)Figure 5.—Information about hunter-killed deer in the study area was obtained through hunter-check stations. (Photo courtesy of L. D. Frenzel.)
An assumption was made that the age structure and incidence of abnormalities in the sample of hunter-killed deer would bereasonably representativeof those in the population at large, an assumption also implicit in a similar comparison made by Pimlottet al.(1969). In this respect, the following statements by Maguire and Severinghaus (1954, p. 109) about deer in New York State are pertinent: "It may be concluded that, considering the open season as a whole, wariness does not significantly distort the age composition of the [deer] kill in relation to that of the corresponding wild population, except possibly for buck seasons of only 1 or 2 days duration.... A reliable appraisal of the age composition of the kill by hunting may be obtained through the operation of roadside checking stations." However, in critically reviewing the present paper Severinghaus stated that in States such as Minnesota, with fewer hunters and higher hunter success rates, age compositions of deer from checking stations may not be the same as those of wild populations. Reviewers Peek and Downing also made similar comments.
Nevertheless, for our comparison with wolf-killed deer it is not necessary that the hunter-kill age structure be exactly representative of the age structure of the actual deer population. All that is required is that there be reasonable agreement between the two. The hunting regulations in our study area allow a 9-day period of taking deer of any age or sex, and a single hunter may legally shoot as many deer as he and his party or associates have permits for. Thus there is no reason for selective hunting, and we feel confident that the age structure of the hunter-kill in our study area does basically represent that of the deer herd at large.
Two laboratory techniques were used for determining the ages of deer from the lower jaws or mandibles—a tooth replacement and wear technique (Severinghaus 1949) and an incisor-sectioning method (Gilbert 1966). The tooth-wear technique requires only the molariform teeth but it is more subjective and inaccurate, particularly in older deer (Ryelet al.1961). Incisor sectioning requires only incisors and appears to be much more accurate.
However, because the incisors had been lost from many of the wolf-kills, and because the tooth-wear technique was used at checking stations, both methods were applied in the laboratory. Mr. David W. Kuehn (1970) sectioned and aged the incisors. Fortunately there was a sufficiently large sample of mandibles with molariform teeth and incisors from both wolf-killed and hunter-killed deer to enable us to devise a table showing the actual ages (based on incisor-sectioning) of each of the jaws assigned to various tooth-wear classes. This table was then used to distribute the ages of specimens that containedonly molariform teeth. For example, because it was found that 37 percent of the jaws aged 4½ years old by tooth wear were actually 5½ years old, we assigned 37 percent of the incisorless jaws aged 4½ by tooth wear to the 5½-year category. Similarly, another conversion chart comparing field age determinations of hunter-killed deer with ages based on incisor sectioning of the same jaws was employed to distribute the ages of field-aged, hunter-killed deer for which jaws or incisors could not be collected.
Figure 6.—All hunter-killed deer examined were checked for age. (Photo courtesy of L. D. Frenzel.)Figure 6.—All hunter-killed deer examined were checked for age. (Photo courtesy of L. D. Frenzel.)
We flew a total of 480 hours during this and related research, mainly during January through March 1967 and December 1968 through March 1969; about one-third of this time was devoted primarily to searching for kills. Jaws were examined from 93 wolf-kills and 49 probable wolf-kills.
Hunter-check stations yielded information from 335 deer (fig. 6), and data on 98 additional hunter-killed deer were contributed by other hunters. Incisors were collected from 82 of 214 hunter-killed deer checked that were older than yearlings; comparisons were then made between ages of the deer based on incisor sectioning and those based on field checks using the wear method. Similarly, incisors were sectioned from 195 wolf-killed and hunter-killed deer older than yearlings that had been aged by the tooth-wear method in the laboratory, so that these two methods could be compared(Kuehn 1970). (Note: incisor-sectioning is unnecessary for fawns and yearlings because animals of these ages can be aged objectively by the progress of tooth replacement.)
Because age or sex distributions might differ in the various subsamples of deer examined during this study, these parameters were compared in subsamples of both wolf-kills and hunter-kills (table 1). No significant differences were found in the age or sex structures between the known wolf-kills and "probable" wolf-kills, so these subsamples were pooled and considered wolf-kills for all subsequent comparisons.
Three significant differences in sex ratio were found among the subsamples of wolf-kills: (1) wolves killed more female fawns than male fawns, but more male adults than female adults (table 2); (2) more of the adults killed in the hunted area were females, while in the wilderness more males were taken (table 3); and (3) after January 1969, when snow was unusually deep, 57 percent of the deer killed were females, compared with only 38 percent before this date.
Table 1.—Results of statistical comparisons between various samples of deer kills from northeastern Minnesota
SamplesizeSample descriptionVSSamplesizeSample descriptionResults of comparisonsDirection ofdifferenceAgestructures[20]Sexratios[21]Wolf-kills:[22]Wolf-kills:[22]93Known49ProbableNonsig.[23]Nonsig.—42Jan.-Mar. 196783Dec. 1968-Mar. 1969Nonsig.Nonsig.—66Male61FemaleNonsig.——50Wilderness area92Hunted areaNonsig.Nonsig.—41Adult, wilderness64Adult, hunted area—Sig., 99 percentMore females in hunted area96Lakes[24]32InlandNonsig.[25]Nonsig.—66Before Feb. 196977After Jan. 1969Nonsig.[26]Sig., 95 percentMore females after Jan.105Adults22Fawns—Sig., 95 percentMore female fawnsHunter-kills:Hunter-kills:110Field aged, 1967225Field aged, 1968Nonsig.Nonsig.—335Field aged98Lab. agedNonsig.Nonsig.—132Lab. aged, males79Lab. aged, femalesNonsig.——89Field aged, fawns246Field aged, adults—Sig., 95 percentMore male adults433Hunter-kills142Wolf-killsSig., 99 percent—Older deer in wolf-kill321Hunter-kills excluding fawns118Wolf-kills excluding fawnsSig., 99 percent—Older deer in wolf-kill
FOOTNOTES:[20]Kolmogorov-Smirnov two-sample test (Siegel 1956).[21]Z test (Downie and Heath 1959).[22]Because test showed no significant differences in age or sex structure between sample of known wolf-kills and probable wolf-kills, these were combined for all subsequent tests and the pooled sample considered "wolf-kills."[23]At 95 percent level or greater. (NOTE: Lack of a significant difference doesnotprove that no difference exists. Rather, it means only that the available evidence does not allow the positive conclusion that a difference does exist.)[24]Wolf-kills found on lakes were compared with those located inland because of the possibility that kills on lakes may not be representative of kills in general.[25]Sample too small for test, but no apparent difference.[26]No significant difference in entire age structures. However, when the percentage of yearlings is compared between the two groups, the difference is almost significant at the 95 percent level.
[20]Kolmogorov-Smirnov two-sample test (Siegel 1956).
[20]Kolmogorov-Smirnov two-sample test (Siegel 1956).
[21]Z test (Downie and Heath 1959).
[21]Z test (Downie and Heath 1959).
[22]Because test showed no significant differences in age or sex structure between sample of known wolf-kills and probable wolf-kills, these were combined for all subsequent tests and the pooled sample considered "wolf-kills."
[22]Because test showed no significant differences in age or sex structure between sample of known wolf-kills and probable wolf-kills, these were combined for all subsequent tests and the pooled sample considered "wolf-kills."
[23]At 95 percent level or greater. (NOTE: Lack of a significant difference doesnotprove that no difference exists. Rather, it means only that the available evidence does not allow the positive conclusion that a difference does exist.)
[23]At 95 percent level or greater. (NOTE: Lack of a significant difference doesnotprove that no difference exists. Rather, it means only that the available evidence does not allow the positive conclusion that a difference does exist.)
[24]Wolf-kills found on lakes were compared with those located inland because of the possibility that kills on lakes may not be representative of kills in general.
[24]Wolf-kills found on lakes were compared with those located inland because of the possibility that kills on lakes may not be representative of kills in general.
[25]Sample too small for test, but no apparent difference.
[25]Sample too small for test, but no apparent difference.
[26]No significant difference in entire age structures. However, when the percentage of yearlings is compared between the two groups, the difference is almost significant at the 95 percent level.
[26]No significant difference in entire age structures. However, when the percentage of yearlings is compared between the two groups, the difference is almost significant at the 95 percent level.
Table 2.—Sex ratios of hunter-killed deer and wolf-killed deer from northeastern Minnesota
AgeHunter-killed deerWolf-killed deerNumberPercentmalePercentfemaleNumberPercentmalePercentfemaleFawns1085050224159Adults31568321055446
In the comparisons of the subsamples of hunter-kills, the only statistically significant difference found was that the adult subsample had a higher proportion of males than the fawn subsample. No significant difference was found in the age structures of the subsamples, so these were all pooled into a sample of 433 hunter-kills for comparison with the wolf-kills. For the same reason, the entire sample of 142 wolf-killed deer was used for a comparison with the hunter-killed sample.
Table 3.—Sex ratios of wolf-killed deer from wilderness areas and from hunted areas
AgeWilderness areaHunted areaTotalNumberPercentmalePercentfemaleNumberPercentmalePercentfemaleNumberPercentmalePercentfemaleFawns40100185050224159Adults4171296444561055644
Wolf-killed deer in our sample, with an average age of 4.7 years, were significantly older (99 percent level) than hunter-killed deer, with an average age of 2.6 years. For example, deer 5 years of age and older made up 48 percent of the wolf-kills but only 10 percent of the hunter-kills (table 4). The oldest hunter-killed deer in our sample was 9½ years old, but the oldest wolf-killed deer was 14½ (fig. 7).
Because of a possible bias against fawns in the method of collecting data from wolf-kills (to be discussed later), the age structure of the sample of wolf-kills excluding fawns was tested against that of the sample of hunter-kills excluding fawns. The result once again was a highly significant difference between these two age structures (table 1).
As an additional test of the degree to which the age structure of the wolf-killed deer might differ from that of the actual population, we compared our wolf-kill age structure with the age structure of a hypothetical deer population. This was considered advisable just in case the hunter-kill data were poorly representative of the age structure of the actual deer herd. Several hypothetical age structures were constructed and compared according to advice from Downing.[27]In all cases, the comparisons produced the same basic results as the tests with the hunter-killed sample. An example of one comparison is given infigure 7.
A further result obtained by aging the wolf-killed deer pertained to the young individuals killed. The deciduous first incisors of fawns and the deciduous premolars of yearlings are usually replaced with permanent teeth by December (Severinghaus 1949). Of 24 wolf-killed fawns examined, however, three (13 percent) taken during January, February, and March had not yet replaced their deciduous first incisors. Of the 13 yearlings found during this same period, nine (70 percent) had failed to replace their deciduous premolars, and two (15 percent) had just replaced them (one deer killed in February and one killed in March).
FOOTNOTES:[27]R. L. Downing. Personal correspondence to L. D. Mech, October 2, 1969.
[27]R. L. Downing. Personal correspondence to L. D. Mech, October 2, 1969.
[27]R. L. Downing. Personal correspondence to L. D. Mech, October 2, 1969.
Table 4.—Age and sex distribution of deer killed by wolves and hunters in northeastern Minnesota
Age(years)Wolf-killed deerHunter-killed deerNumber of:PercentNumber of:PercentMalesFemalesUnknownTotalMalesFemalesUnknownTotalFawns9132241754544112261+5711396326190212+38516114219263153+242864716164154+6341393222155135+129—2115151212866+9211283——3—7+124—161174—1138+42—6451—619+42—641——1—10+—3—32—————11+—1—1}4—————12+—————————13+—1—1—————14+—2—2—————Total66611514210026915410433100
Mandibles from the 142 wolf-killed deer and 259 hunter-killed deer were examined closely for abnormal dentition (table 5,figs. 8-10) (Mechet al.1970) and pathological conditions (table 6), and the lower limbs of 75 wolf-kills and 126 hunter-kills were also checked for abnormalities and pathology (table 7,fig. 11). Statistical comparison showed that the incidence of each condition was significantly higher in the sample from wolf-killed deer (table 8).
Jaw necrosis found in our specimens was similar to that described by Murie (1944) for Dall sheep and Mech (1966a) for moose. Generally animals with this condition are old, and ours were no exception.
Figure 7.—Comparison between the age structures of deer killed by wolves, deer killed by hunters, and a theoretical population from the same general area of northeastern Minnesota.Figure 7.—Comparison between the age structures of deer killed by wolves, deer killed by hunters, and a theoretical population from the same general area of northeastern Minnesota.
Figure 8.—Deciduous first premolar (arrow), usually not present in deer, was found in specimen M-31.Figure 8.—Deciduous first premolar (arrow), usually not present in deer, was found in specimen M-31.
Figure 9.—A permanent first premolar (arrow) was discovered in M-8.Figure 9.—A permanent first premolar (arrow) was discovered in M-8.
Figure 10.—An extra set of fourth premolars (arrows) occurred in specimens M-96.Figure 10.—An extra set of fourth premolars (arrows) occurred in specimens M-96.
Table 5.—Abnormalities in the mandibular dentition of deer from the Superior National Forest, Minnesota
SpecimennumberSexAge[28]Cause ofdeathSide ofjaw[29]AbnormalityYearsM-8F3+WolvesRightP1present (fig. 9)LeftNormal; no P1present outside or inside jawM-31F17 mon.WolvesBothDeciduous P1present (fig. 8) and permanent P1present inside left ramus; right side not examined internallyM-45M4+WolvesRightP2rotated 90°LeftP2absentM-52M4+WolvesRightP2absentLeftNormalM-96F2+HuntersRight2 permanent P4s present; both crooked in orientation (fig. 10)LeftP2diagonal; P3normal; P4below gumline, pointed posteriorly and wedged against M1; appears to have pushed out original P4(fig. 10)M-117M5+HuntersRightThird column of M3reducedM-191M4+WolvesRightThird column of M3absent although rudimentary root presentLeftThird column of M3much reduced, peg-like, and almost separateM-225—4+WolvesRightP2absentLeftP2situated diagonallyM-234F5+WolvesRightThird column of M3reducedM-254M2+HuntersRightP2slightly crooked in orientationLeftP2slanting posteriorly and crowding P3M-272M5+HuntersRightThird column of M3reduced, peg-like, and almost separateLeftThird column of M3peg-like and separated from second column by 4 mm.M-296F5+WolvesRightNormalLeftExtra permanent P4crowding original P4; much like M-96M-369M3+HuntersRightPermanent P2still not emerged but appears to be wedged against root of P3
FOOTNOTES:[28]Based on incisor sectioning method of Gilbert (1966) except that underlined figures are based on tooth replacement or wear (Severinghaus 1949).[29]Where only one side is listed, the other was not available.
[28]Based on incisor sectioning method of Gilbert (1966) except that underlined figures are based on tooth replacement or wear (Severinghaus 1949).
[28]Based on incisor sectioning method of Gilbert (1966) except that underlined figures are based on tooth replacement or wear (Severinghaus 1949).
[29]Where only one side is listed, the other was not available.
[29]Where only one side is listed, the other was not available.
Table 6.—Pathological conditions in the lower jaws of deer killed by wolves or hunters[30]
SpecimennumberSexAgeCause ofdeathApproximatedate ofdeathConditionYearsM-70M6½WolvesFeb. 1968Lump in left side of mandible near M1and M2M-192M7½WolvesJan. 1969Large lump in left diastema apparently from healed fractureM-206M8½WolvesJan. 1969Light necrosis around base of teethM-218M3½WolvesFeb. 1969Large lump in left diastema apparently from healed fractureM-228F11½WolvesMar. 1969Heavy necrosis around molars and extending into bone;half of each M3destroyed, both roots and crownM-236F14½WolvesFeb. 1969Light necrosis around base of teethM-402F10½HuntersNov. 1968Heavy necrosis and lumps on both sides of mandible
FOOTNOTES:[30]Not including dental abnormalities, which are described intable 5.
[30]Not including dental abnormalities, which are described intable 5.
[30]Not including dental abnormalities, which are described intable 5.
The following organs were excised from wolf-killed deer and examined grossly in the field for parasites and abnormalities (fig. 12): lungs (six animals, normal); heart (seven animals, normal); liver (four animals, one small unidentified tapeworm cyst). Twin fetuses were found in each of two adult does examined.
Twelve deer were checked for body fat in one or all of the following areas: back (subcutaneous), kidneys, heart, omenta. Of these animals, seven had large amounts of fat, but five were almost depleted of fat from these stores. These five were all killed in February or March 1969; three were fawns, and two were yearlings that had not yet shed their deciduous premolars.
Of 69 animals examined for femur marrow condition, two had fat-depleted marrow. One was a fawn killed in March 1969 that had not shed its deciduous first incisors, and the other was a 5½-year-old buck killed in February 1966.
A fawn and a yearling that had died in February 1969 from unknown causes also had fat-depleted, marrow. These animals might have been killed by wolves, for wolves had fed on them. However, they could have died from malnutrition and been eaten as carrion.
Table 7.—Pathological conditions in the lower limbs of deer killed by wolves or hunters