Part 5

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.

LITERATURE CITED

Burkholder, B. L. 1959. Movements and behavior of a wolf pack in Alaska. J. Wildl. Manage. 23: 1-11.

Erickson, A. B., Gunvalson, V. E., Stenlund, M. H., Burcalow, D. W., and Blankenship, L. H. 1961. The white-tailed deer of Minnesota. Minn. Dep. Conserv. Tech. Bull. 5, 64 p.

Fuller, W. A., and Novakowski, N. S. 1955. Wolf control operations, Wood Buffalo National Park, 1951-1952. Can. Wildl. Serv., Wildl. Manage. Bull. Ser. 1, No. 11, 23 p.

Goldman, E. A. 1944. The wolves of North America, Part II. Classification of wolves, p. 389-636. Washington, D. C.: The Amer. Wildl. Inst.

Jordan, P. A., Shelton, P. C., and Allen, D. L. 1967. Numbers, turnover, and social structure of the Isle Royale wolf population. Amer. Zool. 7: 233-252.

Kelly, M. W. 1954. Observations afield on Alaskan wolves. Alaska Sci. Conf. Proc. 5: 35 (and mimeo).

Kolenosky, G. B., and Johnston, D. H. 1967. Radio-tracking timber wolves in Ontario. Amer. Zool. 7: 289-303.

Mech, L. D. 1966a. The wolves of Isle Royale. U. S. Nat. Park Serv. Fauna Ser. 7. 210 p.

Mech, L. D. 1966b. Hunting behavior of timber wolves in Minnesota. J. Mammal. 47: 347-348.

Mech, L. D. 1970. The wolf: the ecology and behavior of an endangered species. 389 p. New York: Natural History Press, Doubleday.

Mech, L. D., Kuechle, V. B., Warner, D. W., and Tester, J. R. 1965. A collar for attaching radio transmitters to rabbits, hares, and raccoons. J. Wildl. Manage. 29: 898-902.

Mohr, C. O. 1947. Table of equivalent populations of North American small mammals. Amer. Midl. Nat. 37: 223-249.

Murie, A. 1944. The wolves of Mount McKinley, U. S. Nat. Park Serv. Fauna Ser. 5, 238 p.

Nellis, C. H. 1968. Some methods for capturing coyotes alive. J. Wildl. Manage. 32: 402-405.

Ohmann, L. F., and Ream, R. R. 1969 Vegetation studies in the BWCA--a brief report on plant communities. Naturalist 20(1): 20-29.

Olson, Sigurd F. 1938a. Organization and range of the pack. Ecology 19: 168-170.

Olson, Sigurd F. 1938b. A study in predatory relationship with particular reference to the wolf. Sci. Mon. 46: 323-336.

Pimlott, D. H., Shannon, J. A., and Kolenosky, G. B. 1969. The ecology of the timber wolf in Algonquin Provincial Park. Ont. Dep. Lands and Forests Res. Rep. (Wildlife) 87, 94 p.

Pulliainen, E. 1965. Studies of the wolf (_Canis lupus_ L.) in Finland. Ann. Zool. Fenn. 2: 215-259.

Rausch, R. A. 1967. Some aspects of the population ecology of wolves, Alaska. Amer. Zool. 7: 253-265.

Rutter, R. J., and Pimlott, D. H. 1968. The world of the wolf. 202 p. Philadelphia and N. Y.: J. B. Lippincott Co.

Schenkel, R. 1947. Expression studies of wolves. Behaviour 1: 81-129. (Translation from German by Agnes Klasson.)

Seal, U. S., and Erickson, A. W. 1969. Phencyclidine hydrochloride immobilization of the Carnivora and other mammals. Fed. (Symp. Lab. Anim. Anesthes.) Proc. 28: 1410-1419.

Siegel, S. 1956. Non-parametric statistics for the behavioral sciences. 312 p. New York: McGraw-Hill.

Stenlund, M. H. 1955. A field study of the timber wolf (_Canis lupus_) on the Superior National Forest, Minnesota. Minn. Dep. Conserv. Tech. Bull. 4, 55 p.

Young, S. P. 1944. The wolves of North America, Part I. 385 p. Washington, D. C.: The Amer. Wildl. Inst.

AN ANALYSIS OF THE AGE, SEX, AND CONDITION OF DEER KILLED BY WOLVES IN NORTHEASTERN MINNESOTA

L. David Mech and L. D. Frenzel, Jr.

The selective effect of predation on prey populations is of significance in studies of evolution and population dynamics. Selective predation can be an important agent in the process of natural selection, and it influences the extent to which predators limit the numbers of their prey.

One of the predators most commonly chosen for investigating the selective effect upon prey is the wolf (_Canis lupus_). Because animals preyed upon by wolves generally are large, their remains can be more easily located and examined. It already has been established that in most areas wolves kill primarily young, old, and other inferior members of such prey populations as Dall sheep (_Ovis dalli_), moose (_Alces alces_), caribou (_Rangifer tarandus_), bison (_Bison bison_), and musk-oxen (_Ovibos moschatus_); evidence for this generalization has been summarized by Mech (1970).

However, only recently has it been shown that this generalization may extend to predation on the smallest hoofed prey of the wolf in North America, the white-tailed deer (_Odocoileus virginianus_). Pimlott _et al._ (1969) demonstrated a difference between the age structure of 331 deer killed by wolves during winter in Algonquin Park, Ontario, and 275 deer assumed to represent the actual population in the same area. Whereas only 13 percent of the deer from the population at large were estimated to be more than 5 years old, 58 percent of the wolf-kills were in this age category.

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. The incidence of various abnormalities in wolf-killed deer was also compared with that in hunter-killed animals.

The study was carried out in the Superior National Forest in northern St. Louis, Lake, and Cook Counties of northeastern Minnesota (fig. 1), in conjunction with other aspects of wolf research (see Mech _et al._ p. 1).

METHODS

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.

During the winter of 1968-69 this method of finding kills was supplemented by radiotracking five wolves and their associates via aircraft (see Mech _et 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.

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.

An assumption was made that the age structure and incidence of abnormalities in the sample of hunter-killed deer would be _reasonably representative_ of those in the population at large, an assumption also implicit in a similar comparison made by Pimlott _et 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 (Ryel _et 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 contained only molariform teeth. For example, because it was found that 37 percent of the jaws aged 4-1/2 years old by tooth wear were actually 5-1/2 years old, we assigned 37 percent of the incisorless jaws aged 4-1/2 by tooth wear to the 5-1/2-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.

RESULTS

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_

%: _percent_

:-----------:--:------:------------:--------------------:------------ : : : : : Results of : : : : : : comparisons: : Sample: : :Sample: :--------------------: Direction size :Sample :VS: size :Sample : [20]Age :[21]Sex : of :description: : :description :structures: ratios : difference ------:-----------:--:------:------------:----------:---------:------------ Wolf-kills:[22] Wolf-kills:[22]

93 Known 49 Probable Nonsig.[23] Nonsig. --

42 Jan.-Mar. 83 Dec. 1968- Nonsig. Nonsig. -- 1967 Mar. 1969

66 Male 61 Female Nonsig. -- --

50 Wilderness 92 Hunted area Nonsig. Nonsig. -- area

41 Adult, 64 Adult, -- Sig., More wilderness hunted area 99% females in hunted area

96 Lakes[24] 32 Inland Nonsig.[25] Nonsig. --

66 Before 77 After Nonsig.[26] Sig., More females Feb. 1969 Jan. 1969 95% after Jan.

105 Adults 22 Fawns -- Sig., More female 95% fawns

Hunter-kills: Hunter-kills:

110 Field aged, 225 Field aged, Nonsig. Nonsig. -- 1967 1968

335 Field aged 98 Lab. aged Nonsig. Nonsig. --

132 Lab. aged, 79 Lab. aged, Nonsig. -- -- males females

89 Field aged, 246 Field aged, -- Sig., More male fawns adults 95% adults --------------------------------------------------------------------------- 433 Hunter-kills 142 Wolf-kills Sig., -- Older deer 99% in wolf-kill

321 Hunter-kills 118 Wolf-kills Sig., -- Older deer excluding excluding 99% in wolf-kill fawns fawns ---------------------------------------------------------------------------

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 does _not_ prove 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.

_Table 2.--Sex ratios of hunter-killed deer and wolf-killed deer from northeastern Minnesota_

:--------------------------:------------------------- Age : Hunter-killed deer : Wolf-killed deer -------:--------------------------:------------------------- Number Percent Percent Number Percent Percent male female male female

Fawns 108 50 50 22 41 59 Adults 315 68 32 105 54 46 ------------------------------------------------------------

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_

#: _Number_ %: _percent_

:-------------------:------------------:----------------- Age : Wilderness area : Hunted area : Total -------:-------------------:------------------:----------------- # % % # % % # % % male female male female male female

Fawns 4 0 100 18 50 50 22 41 59 Adults 41 71 29 64 44 56 105 56 44 ----------------------------------------------------------------

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 9-1/2 years old, but the oldest wolf-killed deer was 14-1/2 (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 in figure 7.