Ecological Studies of the Timber Wolf in Northeastern Minnesota Part 8

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 a.s.signed to various tooth-wear cla.s.ses. 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 a.s.signed 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.

[Ill.u.s.tration: _Figure 6.--All hunter-killed deer examined were checked for age. (Photo courtesy of L. D. Frenzel.)_]

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 s.e.x 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 s.e.x 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 s.e.x 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]s.e.x : 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 s.e.x 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.--s.e.x 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.--s.e.x 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).

[Ill.u.s.tration: _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_.]

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.

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).