Once the average rate of kill is known, the average food consumption per wolf can be calculated. The average deer (considering both fawns and adults) from the Superior National Forest during winter weighs about 113 pounds (calculated from Erickson _et al._ 1961), and an arbitrary 13 pounds can be deducted from this for inedible portions.
This leaves 100 pounds of deer per wolf per 18 days, or 5.6 pounds per wolf per day. This figure is much less than the 10 to 14 pounds estimated consumption rate for wolves feeding on moose on Isle Royale (Mech 1966a). However, much variation can be expected in an animal whose physiology must be adapted to a feast-or-famine existence.
Wolves can be maintained in captivity on 2.5 pounds of meat per day, and large active dogs (_Canis familiaris_) require 3.7 pounds per day, so it is likely that the minimum daily requirement for wolves in the wild is about 4.0 pounds per day (Mech 1970). This figure agrees well with the estimated consumption rate for our study area.
FOOTNOTES:
[19] _Kolenosky, G. B. Wolf movements, activities and predation impact on a wintering deer population in East-Central Ontario. (Ma.n.u.script in preparation for publication.)_
Relative Population Density
Censusing wolves in a 1.5-million-acre study area is a difficult task, and we have no direct information on which to base a population estimate. However, some deductions can be made about the relative population densities in our study area between the period 1948 to 1953 and the period of the present study, 1967 to 1969.
R. A. Rausch (1967a) hypothesized that the frequency of large packs is higher when population density is high, and presented evidence supporting this idea. On this a.s.sumption, a comparison of pack-size distributions between various periods can indicate relative population densities between periods. The advantage of this method is that it eliminates the usual type of year-to-year biases in wolf censuses such as might result from differences in precise census route, type of aircraft, skill of observers, and other conditions. Only a difference that would cause a bias in the _size_ of the packs seen would be of importance.
Therefore, we tested the difference in size distributions of population units between the 1948-53 study period and the present period (table 1), using a Kolmogorov-Smirnov two-sample test (Siegel 1956). The average "pack" size in the earlier years was 2.8, compared with 4.2 at present; thus pack sizes are significantly larger at present (95 percent level). This indicates that the population density from 1967 to 1969 may have been higher than from 1948 to 1953. This apparent change may be attributable to a reduction in snaring, trapping, and aerial hunting that took place between the two periods as a result of changes in State game regulations.
A similar comparison between our observations from 1967 and those from 1968-69 (table 1) shows no significant difference between these years, so it appears that the density of wolves in our area has remained about the same over the period of three winters. This agrees with the results of several other studies summarized by Mech (1970) in which wolf populations unaffected by man have been found to remain relatively stable from year to year.
DISCUSSION AND CONCLUSIONS
The movements, behavior, and ecology of the wolves in our study area during winter are variable, and are influenced considerably by snow conditions. This may explain the fact that in late February 1969 wolves 1051, 1053, and 1055 suddenly extended their travels and range (fig.
F-34 and table 4).
However, increased travel may have resulted from other factors. For one thing, the wolves apparently did not need to spend so much time hunting as before. Because of the deep snow, the ability of wolves to capture deer increased, and the animals had a surplus of food. Perhaps under such conditions wolves may use more of their energy for traveling than for hunting.
[Ill.u.s.tration: _Figure 34.--Net weekly (straight-line) distances traveled by three radiotagged wolves._]
In this respect it is interesting that 1051 moved right out of his area and traveled into country that presumably was unknown to him. Wolves 1053 and 1055 each ventured into an area that was almost devoid of deer and that even had few moose in it. Without sufficient fat reserves in all these animals, it would seem disadvantageous for them to have made these travels.
Evidently wolves can obtain enough food in much smaller areas than these three animals used after February. Both 1059"s pack of five and 1057 lived in relatively small areas throughout the winter and seemed to survive well. Before late February, 1051, 1053, and 1055 did also.
Thus some factor other than food must have influenced the movements of these three animals from late February through April.
The fact that the increased movement began during the breeding season makes one suspect a relationship between the two. One possibility is that the factors increasing the hormonal flow a.s.sociated with breeding in adults stimulate a hormone output in immature or subordinate individuals that causes an increase in their movements. An alternative is that the breeding behavior of resident packs involves the beginning of, or an increase in, aggression toward neighboring nonmembers. This might force the lone animals to shift about over large areas in avoidance of such aggression.
Whatever the cause of the changes in movements of these animals, the fact that the pack used a much smaller area than any of the lone wolves may be of central importance in trying to understand the organization of the wolf population. The following pieces of information are also pertinent to such an understanding: (1) the pack, which can be presumed to include a breeding pair (Mech 1970), chased other wolves in its area; (2) the lone wolves, which apparently did not breed, were tolerant of, or indifferent to, other lone wolves in their areas; (3) the ranges of the lone wolves overlapped considerably (fig. 35); (4) the lone wolves seemed to avoid certain large areas that one might logically think would have been visited by them (fig. 35); and (5) packs of wolves were sometimes observed in these large areas (fig. 35).
[Ill.u.s.tration: _Figure 35.--Locations of all radiotagged wolves and unmarked packs observed during winter 1968-69, except dispersal of 1051 out of the study area. Only selected lakes shown._]
From the above information it can be hypothesized that the wolf population consists basically of groups of breeding packs defending territories of limited size, with lone wolves and other nonbreeding population units that are tolerant of each other shifting about in much larger nonexclusive areas among these territories. The information from Isle Royale (Mech 1966a, Jordan _et al._ 1967) is consistent with this idea, but the area of that island (210 square miles) is too small to allow untested extrapolations to be made about s.p.a.cing in much larger wolf populations. Data from Algonquin Park, Ontario (Pimlott _et al._ 1969) also strongly suggest this hypothesis. However, the packs studied there could not be identified with certainty, and little information was obtained about nonbreeding population units.
To test the proposed hypothesis with certainty, a larger number of identifiable breeding and nonbreeding population units from the same general area must be followed during at least one winter. This will be the main objective of our next study.
SUMMARY
During the winters of 1966-67, 1967-68, and 1968-69, aerial observations of timber wolves (_Canis lupus_) were made in the Superior National Forest in northeastern Minnesota, where the primary prey is white-tailed deer (_Odocoileus virginia.n.u.s_). In 480 hours of flying during the study, 77 sightings involving 323 wolves were made. In addition, during 1968-69, five radiotagged wolves and their a.s.sociates were tracked via receivers in aircraft for a total of 570 "wolf-days."
Visual observations were made during 65 percent of the times the wolves were located from December through April.
The average size of each population unit (including single wolves, pairs, and packs) observed was 4.2, although packs of as many as 13 wolves were sighted. Radiotagged wolves spent most of their daylight hours resting during winter, and when traveling, hunting or feeding during the day, tended to do so before 11:00 a.m. and after 3:00 p.m.
Considerable variation was discovered in the movement patterns of individual wolves, with straight line distances between consecutive daily locations ranging from 0.0 to 12.8 miles, and between weekly locations, 0.0 to 49.0 miles. A pack of five wolves used a range about 43 square miles in extent, whereas lone wolves covered areas many times this size. 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. Wolves generally consumed all the flesh and much of the hair and bones from kills, except during February and March 1969 when extreme snow conditions increased the vulnerability of deer to an unusual degree. At that time kills were found that were partly or totally uneaten. The kill rate by radiotagged wolves and a.s.sociates during the winter of 1968-69, based on 468 wolf-days of data, varied from one deer per 6.3 days to one per 37.5 days per wolf, with the average being one deer per 10 to 13 days. The rate was much lower per wolf for members of the pack of five than for lone wolves, and much lower before February 1, 1969, than after. The average rate of kill during more usual winters was estimated to be about one deer per 18 days. This is a consumption rate of about 5.6 pounds of deer per wolf per day.
Indirect evidence based on comparisons of pack-size distributions for different periods indicates that the wolf density in the study area may have increased since 1953, but that it has remained the same from 1967 to 1969.
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.
ACKNOWLEDGMENTS
This study was supported by Macalester College, the U.S. Bureau of Sport Fisheries and Wildlife, the USDA Forest Service, the Minnesota Department of Conservation, and the New York Zoological Society.
Special thanks are due the following for their help and cooperation with this project: Mr. J. O. Wernham, former Supervisor, Mr. L. T.
Magnus, Wildlife Biologist, numerous District Rangers, and other supporting personnel of the Superior National Forest, Mr. J. T. Morgan, North Central Forest Experiment Station; and Mr. S. E. Jorgensen and Mr. C. E. Faulkner, U.S. Bureau of Sport Fisheries and Wildlife.
Drs. C. T. Cushwa, L. F. Ohmann, Catherine Ream, and D. G. Schneider aided in the field work. Mr. W. W. Cochran provided advice and suggestions on the radiotracking technique, Dr. U. S. Seal furnished the drugs and the advice on their use with wolves, and Mr. R. Himes contributed significantly in the wolf trapping. Mr. L. Ringham, Ontario Department of Lands and Forests, granted permission for research personnel to radiotrack wolves crossing into Quetico Park, Canada.
Numerous students from Macalester College also contributed to the field effort.
Thanks are also due pilots Robert Hodge, Pat Magie, Ken Bellos, Don Murray, Jack Burgess, and several others, who along with pilot-biologist John Winship, expertly flew the aircraft used in the study.
This report was reviewed by the following biologists: Mr. G. B.
Kolenosky, Dr. P. A. Jordan, Mr. M. H. Stenlund, and Dr. D. L. Allen.
Mr. Wallace C. Dayton, Miss Elizabeth Dayton, and the Quetico-Superior Foundation, all of Minneapolis, generously contributed funds to support Mech during the preparation of the paper.
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