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.
[Illustration: _Figure 2.--Wolves were located from the air, usually on
frozen lakes. (Photo courtesy of L. D. Mech.)_]
[Illustration: _Figure 3.--Wolf-kills were easily spotted from
aircraft. (Photo courtesy of L. D. Mech.)_]
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.
[Illustration: _Figure 4.--As many wolf-killed deer as possible were
examined from the ground. (Photo courtesy of L. D. Mech.)_]
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.
[Illustration: _Figure 5.--Information about hunter-killed deer in the
study area was obtained through hunter-check stations. (Photo courtesy
of L. D. Frenzel.)_]
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.