Part 6

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_.

_Table 4.--Age and sex distribution of deer killed by wolves and hunters in northeastern Minnesota_

:-------------------------------:------------------------------- : Wolf-killed deer : Hunter-killed deer Age :---------------------------:---:---------------------------:--- (years): Number of: : : Number of: : :Males Females Unknown Total: % :Males Females Unknown Total: % -------:---------------------------:---:---------------------------:--- Fawns 9 13 2 24 17 54 54 4 112 26 1+ 5 7 1 13 9 63 26 1 90 21 2+ 3 8 5 16 11 42 19 2 63 15 3+ 2 4 2 8 6 47 16 1 64 15 4+ 6 3 4 13 9 32 22 1 55 13 5+ 12 9 -- 21 15 15 12 1 28 6 6+ 9 2 1 12 8 3 -- -- 3 -- 7+ 12 4 -- 16 11 7 4 -- 11 3 8+ 4 2 -- 6 4 5 1 -- 6 1 9+ 4 2 -- 6 4 1 -- -- 1 -- 10+ -- 3 -- 3 2 -- -- -- -- -- 11+ -- 1 -- 1 } -- -- -- -- -- 12+ -- -- -- -- } 4 -- -- -- -- -- 13+ -- 1 -- 1 } -- -- -- -- -- 14+ -- 2 -- 2 } -- -- -- -- --

Total 66 61 15 142 100 269 154 10 433 100 -----------------------------------------------------------------------

Mandibles from the 142 wolf-killed deer and 259 hunter-killed deer were examined closely for abnormal dentition (table 5, figs. 8-10) (Mech _et 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.

_Table 5.--Abnormalities in the mandibular dentition of deer from the Superior National Forest, Minnesota_

:---:-------:--------:-------:-------------------------------- Specimen: : :Cause of:Side of: number :Sex:Age[28]: death :jaw[29]: Abnormality --------:---:-------:--------:-------:-------------------------------- _Years_

M-8 F 3+ Wolves Right P_1 present (fig. 9) Left Normal; no P_1 present outside or inside jaw

M-31 F _17 mon._ Wolves Both Deciduous P_1 present (fig. 8) and permanent P_1 present inside left ramus; right side not examined internally

M-45 M _4+_ Wolves Right P_2 rotated 90° Left P_2 absent

M-52 M 4+ Wolves Right P_2 absent Left Normal

M-96 F _2+_ Hunters Right 2 permanent P_4s present; both crooked in orientation (fig. 10) Left P_2 diagonal; P_3 normal; P_4 below gumline, pointed posteriorly and wedged against M_1; appears to have pushed out original P_4 (fig. 10)

M-117 M 5+ Hunters Right Third column of M_3 reduced

M-191 M 4+ Wolves Right Third column of M_3 absent although rudimentary root present Left Third column of M_3 much reduced, peg-like, and almost separate

M-225 -- 4+ Wolves Right P_2 absent Left P_2 situated diagonally

M-234 F 5+ Wolves Right Third column of M_3 reduced

M-254 M 2+ Hunters Right P_2 slightly crooked in orientation Left P_2 slanting posteriorly and crowding P_3

M-272 M 5+ Hunters Right Third column of M_3 reduced, peg-like, and almost separate Left Third column of M_3 peg-like and separated from second column by 4 mm.

M-296 F 5+ Wolves Right Normal Left Extra permanent P_4 crowding original P_4; much like M-96

M-369 M 3+ Hunters Right Permanent P_2 still not emerged but appears to be wedged against root of P_3 --------:---:-------:--------:-------:--------------------------------

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.

_Table 6.--Pathological conditions in the lower jaws of deer killed by wolves or hunters[30]_

:---:------:--------:-----------:----------------------------- Specimen: : :Cause of:Approximate: number :Sex: Age : death : date of : Condition : : : : death : --------:---:------:--------:-----------:----------------------------- _Years_

M-70 M 6-1/2 Wolves Feb. 1968 Lump in left side of mandible near M_1 and M_2

M-192 M 7-1/2 Wolves Jan. 1969 Large lump in left diastema apparently from healed fracture

M-206 M 8-1/2 Wolves Jan. 1969 Light necrosis around base of teeth

M-218 M 3-1/2 Wolves Feb. 1969 Large lump in left diastema apparently from healed fracture

M-228 F 11-1/2 Wolves Mar. 1969 Heavy necrosis around molars and extending into bone; half of each M_3 destroyed, both roots and crown

M-236 F 14-1/2 Wolves Feb. 1969 Light necrosis around base of teeth

M-402 F 10-1/2 Hunters Nov. 1968 Heavy necrosis and lumps on both sides of mandible --------:---:------:--------:-----------:-----------------------------

FOOTNOTES:

[30] Not including dental abnormalities, which are described in table 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 5-1/2-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_

:---:-----:------:-------------------------------------------- : : :Cause : Specimen:Sex: Age : of : Condition number : : :death : --------:---:-----:------:-------------------------------------------- _Years_

M-28 M 5-1/2 Wolves Right hind foot: "Old healed ankylosis of the pastern joint ... a spontaneously healed bacterial arthritis with the destroyed joint cavity filled in by solid bone. This deer probably had defective gait"[31] (fig. 14).

M-29 F 5-1/2 Wolves Front foot: "A 3×4×5 cm. fibrous mass in the subcutis about the digital flexor tendon on the volar surface of the metacarpus. The surface was denuded, ulcerated, and superficially infected by surface bacteria.... Probably did detract from the animal's speed of flight"[31] (fig. 15).

M-37 F 7-1/2 Wolves Hind foot: "Probable that the lesion was at one time an active bacterial bone marrow infection that had eventually fistulated to the skin.... Regional tendons and their sheaths were also present among this inflammation and scarring, and it would be fair to assume that the animal's agility was impaired to some extent."[31]

M-115 M 4-1/2 Hunter Right front hoof: Broken at tip.

M-196 F 4-1/2 Wolves Left front foot: "Two severe transverse lacerations on the volar surface. Each was approximately 4 cm. in length. One was located at the margin of the heel, and the other was located several cm. proximad. The more proximal wound had severed the flexon tendons, and the consequent uselessness of the limb was suggested by the splayed toes, the unmarred hoof wall and unworn soles"[32] (fig. 16).

M-227 M 9-1/2 Wolves Left hind leg: "A diffuse swelling of the distal metatarsal bone, the surface of which was studded with small osteophytic spicules. The major flexor and extensor tendons were forced to assume a convex course over the summits of the dorsal and plantar surfaces of the defect, but the tendon sheaths were clean and the normal wear on soles of the involved toes suggested that functional deficit and pain were probably minimal ... quite certainly a callus from previous fracture"[32] (fig. 17). --------:---:-----:------:-------------------------------------------- 1 FOOTNOTES:

[31] D. M. Barnes. Personal correspondence to L. D. Mech, April 11, 1967.

[32] D. M. Barnes. Undated laboratory report transmitted to L. D. Mech in 1969.

DISCUSSION AND CONCLUSIONS

It has been established that wolves hunting Dall sheep (Murie 1944), caribou (Crisler 1956), moose (Mech 1966a), and other species usually have a low percentage of success. In the case of a pack of 15 wolves hunting moose on Isle Royale during winter, only 4.6 percent of all the moose detected by the pack were killed; considering only the moose that the wolves caught up to or held at bay, the kill rate was 7.6 percent (Mech 1966a).

What little evidence there is about wolves hunting deer indicates that the success rate is also low with this prey species, at least in winter. The senior author has now observed a total of 14 deer being chased by wolves in northeastern Minnesota, mostly by packs of five, seven or eight wolves (Mech 1966b, and see Mech _et al._, p. 1). In only one case (6.7 percent) did the wolves (a pair) succeed in catching their prey.

Low hunting success rates imply that the circumstances influencing hunts are seldom favorable enough, or the prey animals encountered are seldom vulnerable enough for the wolves to succeed. When the evidence cited earlier that most wolf-killed animals are inferior members of their populations is considered, the most cogent explanation for the low hunting success of wolves is that relatively few prey animals are vulnerable.

_Table 8.--Incidence of various abnormalities and pathological conditions in wolf-killed deer compared with that in hunter-killed deer_

#: _Number_ %: _Percent_

:----------------:----------------:------------- : Wolf-kills : Hunter-kills : :------:---------:------:---------: Level of Condition : Deer : Deer : Deer : Deer : significance : in : with : in : with : :sample:condition:sample:condition: ---------------------:------:---------:------:---------:------------- # # % # # % %

Dental abnormalities 142 8 5.6 259 5 1.9 [34]90

Jaw necrosis, lumps, 142 6 4.2 259 1 0.4 [34]95 or fractures[33]

Pathology of lower 75 5 6.7 126 1 0.8 95 limbs ---------------------:------:---------:------:---------:-------------

FOOTNOTES:

[33] Two mandibles from wolf-killed deer had large lumps from healed fractures in the region of the diastemas.

[34] If all dental and jaw abnormalities are pooled, the difference between the incidence in the wolf-kill sample (9.8 percent) and that in the hunter-kill (2.3 percent) is significant at the 99 percent level.

Age Structure

Our data strongly indicate that in northeastern Minnesota wolves prey much more heavily on the older members of the deer population, at least during winter (fig. 7). Substantial vulnerability to wolves seems to begin at about the age of 5 years (fig. 13), because the percentage of wolf-killed deer in each year class increases from 9 percent for 4-1/2-year-old animals to 15 percent for 5-1/2-year-olds (table 4). Indeed, 48 percent of the wolf-kills were aged 5-1/2 and over, which compares favorably with the Ontario figure of 58 percent for these age classes (Pimlott _et al._ 1969).

These figures assume added significance when compared with a sample of deer killed by hunters in the same general area (fig. 1). Only 10 percent of the hunter-killed deer were 5-1/2 years old or older, and the percent killed in each year class dropped off suddenly from 13 percent aged 4-1/2 to 6 percent aged 5-1/2. If the age structure of the hunter-kill sample is reasonably representative of the age structure of the population at large, the wolf-kill data show that wolf predation in our study area during winter has a definite selective effect on the deer population.

There is no direct way of knowing that the age structure of the hunter-killed deer represents the age structure of the deer population at large. However, sampling hunter-kills is the most practical means available for gaining an index to the age structure of the existing herd. Further, there are three indirect pieces of evidence indicating that the hunter-kill sample represents the actual age structure of the population, just as Maguire and Severinghaus (1954) found in New York. First, our sample has the basic theoretical form expected of a stable deer herd; i.e., the youngest year class contained the most members, and each older cohort included fewer (fig. 7). Second, the age structure of our sample has the same form as most other deer age structures from widely diverse areas, (Ontario, Pimlott _et al._ 1969; southern Minnesota, Erickson _et al._ 1961; Massachusetts, Shaw 1951). Third, there is no reason to believe that in our area rifle hunting is especially selective for any particular age classes. In talking with large numbers of hunters, we have learned that most shoot at any and all deer they happen to see.

Even if the age structure of the hunter-kill sample did not approximate that of the actual herd, the comparison of the wolf-kill with the theoretical population dictates the same conclusion: the rate of kill of older deer by wolves was several times greater than that of younger deer, excluding fawns (fig. 13). In any case, if the actual deer population in our study area had an age structure similar to that of our sample of wolf-kills (which would be the only age structure that would contradict our conclusion), its numbers would be declining by orders of magnitude each year, and there would now be only a remnant population. Such obviously is not the case.

The only other question that might arise from a comparison of the age structure of our wolf-killed deer with that of the hunter-killed deer concerns the area from which each sample was taken. Fifty of our wolf-kills came from a region almost inaccessible to hunters (fig. 1). However, the other 92 came from the same general area as the hunter-kills. Nevertheless, there was no statistically significant difference in age structure between the wolf-kills from the wilderness versus those from the hunted area (table 1). This fact also suggests that the human hunting in the area is relatively light and has little effect on the age structure of the deer population in the area.

Wolves may also be taking a disproportionately high number of fawns, although our data do not show this. Nevertheless, there may be a bias against fawns in our method. It is not unusual to discover the remains of a wolf-killed deer so completely eaten that there is no indication left of the animal's age. Because fawns often are only about half the size of adult deer, and their skeletons have not yet completely ossified, the chances are better that fawns will be more completely eaten. Pimlott _et al._ (1969) also recognized this possible bias, although their data did indicate that wolves were killing a higher percentage of fawns than occurred in the population.

Our study does support the other conclusion of Pimlott _et al._ (1969), based on a study of 331 kills, that wolf predation on deer during winter shows a definite selection for older animals. It does not agree with the tentative conclusion of Stenlund (1955) that wolves in the Superior National Forest do not prey disproportionately on old deer. However, Stenlund's conclusion was based on 36 kills and on the assumption that only deer at least 7 years old were "old." Deer 5 years old and older composed 33 percent of Stenlund's sample, a figure considerably higher than the 10 percent in these age classes in our hunter-kill sample (table 4). Thus Stenlund's data do not contradict our conclusion.

The age of 5 years seems to be the beginning of the period of vulnerability for adult deer. Although 5 years might not seem especially old, there are two aspects of significance concerning deer of this age and older. First, they are in the second half of the life span for most members of the species, and their alertness and ability to bolt quickly away might be expected to decline. It is of interest in this regard that Klein and Olson (1960, p. 87) believed 5 years of age to be "the upper limit of physiological efficiency" of black-tailed deer (_Odocoileus hemionus_) in Alaska. Second, up to the age of at least 4-1/2 years, and perhaps beyond, the apparent weight-load-on-track of deer increases with age (Kelsall 1969). Thus older deer would sink farther into the snow than younger ones, and their escape might be slowed and hindered more. For further discussion of the effect of snow on the vulnerability of deer, see Mech _et al._ (p. 51).

Sex Ratio

Statistical tests comparing a number of subsamples of both wolf-killed deer and hunter-killed deer showed a series of significantly different sex ratios (tables 1-3). The ratio of males to females in the fawn cohort of the hunter-kill, which is probably the most representative of the actual fawn sex ratio, was even (table 2). With wolf-kills, however, a significantly higher percentage of females was taken in the fawn subsample (59 percent) than in the adult subsample (46 percent). These results compare favorably with those of Stenlund (1955), who found that from 1948 to 1953 in the same area as the present study 68 percent of 19 sexable fawn wolf-kills were females and 44 percent of 63 sexable adult wolf-kills were females.

If the sex ratio of fawns began even, and more females than males were killed by wolves, then a higher proportion of males would be left in the adult population, unless some other mortality factor kills more male fawns. Thus it is not surprising that in the wilderness area, where little or no hunting is done, the sex ratio of wolf-kills in the adult cohort is significantly heavy toward males (71 percent: 29 percent). This was also true of the wolf-kills in Algonquin Provincial Park, where males made up 57 percent of the total sexable wolf-kill (Pimlott _et al._ 1969). The latter figure may even have been higher if calculated for adults alone, for a preponderance of female fawns in the Algonquin Park data (such as occurred in our and Stenlund's samples) would tend to obscure the preponderance of males in the adult sample.

The adult subsample of hunter-kills also contained a higher percentage of males (66 percent : 34 percent). Although this might also reflect the influence of wolf predation on female fawns, it probably is more a result of the greater movement of bucks during the hunting season, which overlaps with the rutting season. Even the sex ratio of adult deer killed in wolf-free areas shows a preponderance of males (Erickson _et al._ 1961).