Louis Daniel Frenzel

“ This may be the wolf's favorite part of a deer, for the stomach of one wolf that we examined in January 1967 contained nothing but such fat.
The average consumption and kill rate of deer by wolves has not yet been determined, but we have some information bearing on the subject. Because our data were obtained during a winter of unusually deep snow, and it was obvious that wolves were killing more deer than they could eat at the moment (see Mech et al., page 51) , our figures should be considered much higher than average. ”

“ Significantly higher incidences of abnormalities and pathological conditions of both mandibles and lower limbs were found in wolf-killed deer than in hunter-killed deer, and these conditions are described. It is concluded that wolf predation on white-tailed deer in the study area during winter generally is selective in that it tends to remove members of the prey population that are old, debilitated, or abnormal. Apparently these classes of deer represent such a small percentage of the population that they are seldom taken by human hunters. ”

“ 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. ”

“ In conclusion, our data on both age and condition of wolf-killed deer show that at least during winter, wolves in our study area usually do not kill just any deer they discover, although they do try to. Evidently, most deer can usually escape wolf predation. The most frequent exceptions are those 51⁄2 years old and older, those born late, those suffering from poor nutrition, those with abnormalities or pathological conditions, and possibly fawns. ”

“ 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) . ”

“ Although both wolves and deer floundered in the extremely deep snow, the relatively lighter weight-load-on-track of wolves evidently gave [Pg 59] them a greater advantage than under the usual snow conditions, when wolves were observed floundering more than deer. This factor, plus a decline in the health and vigor of some segments of the deer population and a tendency for deer to congregate on frozen lakes, where wolves have an advantage, help explain the increased vulnerability of deer to wolf predation during the winters of deep snow. ”

“ Thus we feel that an estimated kill rate of about one deer per 18 days per wolf is a close approximation of the average kill rate for most winters. This is about 50 percent less than the kill rate of one deer per 4 days estimated by Stenlund (1955) for two packs of three wolves (one deer per 12 days per wolf) . However, it compares favorably with the actual kill rate of one deer per wolf per 17.6 days found for a pack of eight wolves in Ontario. ”

“ Hunting, Killing, and Feeding Behavior
The primary prey of most wolves in our study area is the white-tailed deer (fig. 29) , but some moose (fig. 30) are also killed. We have examined the remains of six moose that were eaten by wolves, two of which were killed by them (fig. 31) . One was found on February 25, 1967, on Gillis Lake and the other on March 7, 1969, on Twinkle Lake. These locations are within 3 miles of each other, suggesting that a wolf pack in that area may be more accustomed to preying on moose than other packs. ”

“ Wolves that have ranges small enough to cover in a few days form a network of their own trails, which they can maintain merely by traveling regularly over them. Packs on Isle Royale depended a great deal on such a system of trails (Mech 1966a) , and so did Pack No. 1059 in our study area.
Wolf packs can travel up to 45 miles in a day but it is usually larger packs that do so (Stenlund 1955, Burkholder 1959, Mech 1966a, Pimlott et al. 1969) . In our study area we sometimes saw evidence of long moves by large packs along strings of lakes and waterways. ”

“ It is significant that the pack of five wolves had a lower kill rate per wolf than did single wolves and pairs. This is explainable because the ability of wolves to kill deer during early 1969 was much greater than usual (see Mech et al., p. 51) . Thus single wolves probably could kill deer just as easily as could packs, but they did not need to share them. This differs markedly from the situation on Isle Royale, where lone wolves usually feed only on moose remains left by packs (Mech 1966a, Jordan et al. 1967) . ”

“ We employed a similar analysis for deer killed by wolves in northeastern Minnesota, but used a more refined aging technique and included comparisons of the age and sex structures of various subsamples of wolf-kills. Whereas the Ontario research involved a prey population unlimited by man, our work was carried out on both a hunted population and on one relatively unhunted. Further comparisons were made between deer killed during periods of normal snow conditions and those taken during unusually high snow accumulations. ”

“ This is because until the snow becomes dense enough to hold a running deer, each increase in density would further the advantage of the wolf, which would require only half the density to support it, while it would hinder the deer. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ However, frozen lakes also provide wolves with good running conditions, and even seem to give them an advantage (Rutter and Pimlott 1968, Mech 1970) , so many of these deer were killed (fig. 11) .
Figure 11.—On frozen lakes, wolves often seem to have the advantage over deer, such as in this case where the wolf (center) has just killed a deer and is trying to discourage a raven from joining him in the feed. ”

“ This implies that extreme or unusual conditions might sometimes occur, to which either the wolf or the deer is poorly adapted.
One of the most important environmental factors that can influence the interactions of wolves and deer is snow. The total fall, depth on the ground, and the density are all aspects of snow that may vary considerably and affect the ability of wolves to capture deer. ”

“ Under more usual conditions, a running deer might sink through the snow to the ground and thus obtain a firm footing from which to spring again. In discussing wolf-caribou relations in snow, Kelsall (1968, p. 249) stated the following: "While caribou (Rangifer tarandus) will sink into snow even deeper than wolves, their longer legs permit them to run efficiently where a wolf will bog down. Nasimovich (1955) considered that roe deer and sika deer could be taken by wolves when snow was not more than 30 cm. ”

“ Because wolves in the known range of nubilus are thought to be extinct, and because the animals in northeastern Minnesota are legally unprotected and subject to a control program, it seems highly desirable that the question of their taxonomy be studied intensively while specimens are still available. ”

“ One animal in an apparent dispersal was tracked a straight line distance of 129 miles between extreme points.
A reddish male wolf was the leader of the pack of five and led two observed chases after alien wolves in the pack's territory. This animal was also most active during scent marking by the pack. Lone wolves were apparently indifferent to other wolves, and thus exclusive areas, or territories, were not observed among lone wolves.
Hunts involving a total of seven deer were observed and described, and two successful attacks on deer were interpreted from tracks in the snow. ”

“ 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. ”

“ On the basis of data presented in this paper, the following hypothesis about the organization of the wolf population studied is proposed: The wolf population consists basically of groups of breeding packs defending territories of limited size, with lone wolves and other nonbreeding population units, tolerant of each other, shifting about in much larger nonexclusive areas among these territories. ”

“ 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 [Pg 40] (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.) ”

“ However, it appears that when snow becomes extremely deep, wolves then gain the advantage. With 22 to 48 inches or more of snow to plow through, a deer would have trouble even touching a firm foundation. According to Kelsall (1969) , deer measure only 20 to 24 inches from hoof tip to chest, with legs extended.
It is true that wolves stand even shorter than deer and so might be expected to flounder even more. However, this is where another factor becomes important, the "weight-load-on-track" or total weight per area of track. ”

“ For wolves, this measure varies from 89 to 103 gm./cm.2 (Foromozov 1946) . This means that for the same amount of force applied during running, a wolf would have twice as much support as a deer. It also means that in deep snow a walking wolf generally is much less restricted than a walking deer. Late in February 1969, for example, when deer were seriously limited in their ability to travel, wolves were able to travel widely (Mech et al., p. 1) . ”

“ 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. ”