By Tim Eisele Correspondent
Madison — The DNR received a positive review of its Sex-Age-Kill
model that’s used as the basis of its deer season
Mark Boyce, wildlife professor at the University of Alberta, was
one of six experts from outside the state selected by a steering
committee of state conservation groups to examine the SAK and
report on whether it is doing the best job it can to manage deer in
Wisconsin, or whether there was a better model.
Boyce told the Natural Resources Board at its meeting Dec. 5
that it was a consensus of the committee that, “Wisconsin is
probably doing the best job of any state in the U.S. in terms of
its conscientious, statistically rigorous approach to managing
white-tailed deer. There isn’t any place in the U.S. that does a
better job than Wisconsin.”
Wisconsin collects more demographic information, on an annual
basis, to monitor the deer population than any of the 21 states the
experts surveyed. The DNR, the report states, should be commended
for its efforts to track deer population dynamics.
Can it be improved? The panel, in its preliminary draft report
which is expected to become final in January, said yes, that it
would recommend combining the 130 deer management units into larger
areas, which would reduce the number of units.
It also believes there are some units, one of which is Unit 28
in the Ashland area, where the model works poorly.
One of the questions the panel was asked to look at was, “Are
the techniques used by DNR suitable for managing deer in
Wisconsin?” In general, panelists agreed, but said there were some
uncertainties that need focused attention.
They looked at other models but said that there probably were no
better models for use in Wisconsin.
“We reviewed other methods used by other states and published in
the literature, but none of them matched up to what is now used in
Wisconsin,” Boyce said.
But he thought there was a need for an in-depth demographic
study to evaluate the buck recovery rate, to estimate mortality
rates, and examine
how survival and reproduction vary. These would be major studies
that would take several years of research.
Boyce said the committee evaluated the assumptions of the SAK,
evaluated the precision of the SAK, and adjustments made by the
“Fluctuations in the buck harvest rate have disturbing
consequences to the SAK, and the assumption is that it is constant,
but it does change,” Boyce said. “In reality, any population of
animals undergoes random fluctuations in survival and reproduction
In studying sampling error, the experts looked at data that go
into the SAK, such as the fawn-to-doe ratio, but it was not
possible to come up with a calculation of precision because some of
the values are not known. This includes things such as the wounding
loss, or how many hunters do not register their deer. Those numbers
are not known, but they are estimated.
Boyce said he was surprised there was no one input variable that
was always the most important variable. For instance, sex ratio,
fetal sex ratio, buck recovery rate, or fawn-to-doe ratios
contribute to the estimate of the number of deer, and all are
The panel looked at several other methods which might be used in
place of SAK, which included index methods, distance sampling,
aerial surveys, change-in-ratio methods, catch-per-unit-effort
models, population reconstruction techniques, and statistical
age-at-harvest models. SAK does quite well relative to these
alternatives, he said, with the only method that might have some
potential being the statistical age-at-harvest method, though it
has not yet stood the test of time.
When surveying other states, panelists found that nine use SAK,
two-thirds of which have mandatory registration; most use mail
surveys to count the harvest; and one-fourth do not estimate the
herd population size.
“Wisconsin has one of the most thorough deer management
programs,” Boyce said. “The state exceeds all states in
transparency and amount of information made available to the
Their conclusion: Wisconsin collects more information than any
state the panel surveyed.
There are some units where SAK does a very poor job, and those
should receive special attention to learn what is wrong there.
“We were disappointed in the population growth measure in the
northern units,” he added.
Boyce acknowledged that there may be some confusion by hunters
in population counts reported in deer per square mile of habitat,
because the amount of habitat can change each year.
The summer fawn-to-doe ratio obtained during the summer can
result in a bias because in July does are still hiding fawns. Only
August to September data should be used to estimate the ratio, the
Christine Thomas, chair of the NRB Land Committee, said this was
the first time the results of the audit were released. She asked
the DNR to report back to the board with changes it intends to make
as a result of the report.
She wanted to make certain state citizens knew the board took
the report seriously, and asked Boyce if anyone on the board or the
staff influenced him.
“Absolutely not,” he said.
In a question from Jonathan Ela, board member from Madison,
about how many fewer units were needed, Boyce said he thought there
were two or three times as many DMUs now as are needed. By making
the units larger, it would help make predictions more precise.
Thomas commented that no matter how good the panel says the SAK
is, every deer hunter still wants to know how many deer are under
or around his/her deer stand, but there is no way of getting that
Gerry O’Brien, board chairman, asked if Boyce thought the board
should feel comfortable that the SAK is a reliable method.
“We conclude that the SAK method overall works well in
Wisconsin, but we make recommendations that the DNR not use it
where it uses earn-a-buck,” Boyce said. “SAK works well most of the
time, and from a management standpoint over a vast area, it may be
the best that can be done.”
DNR deer ecologist Keith Warnke said the DNR couldn’t agree
more, as the DNR does not use SAK in EAB or CWD units. For those
units, the DNR uses other models, including aerial surveys of deer
Some members of the steering committee asked questions.
Greg Kazmierski, of the Wisconsin Deer Hunters Coalition and
Safari Club International, asked about ways that hunters could be
involved in some of the surveys to increase the accuracy of
surveys. Boyce said it would be possible to participate in summer
fawn surveys under the review of a statistician.
Kazmierski said he had concerns about the buck recovery rate,
and will be examining the report and coming back to the panel with
“Professor Boyce confirmed many hunters’ observations and
beliefs by clarifying SAK population estimates for individual units
are within plus or minus 30 to 40 percent of actual population
size,” Kazmierski said. “This is an unacceptable variance and we
hope that recommendations to correct the problem will move
Mark Noll, of the Conservation Congress, said the public has a
real problem understanding winter deer density estimates, and
wondered if goals should be expressed in other ways. Boyce said
that one problem for the public is knowing how much habitat there
is in a unit.
Gerry O’Brien commented afterward that he “was impressed” by the
fact he thinks the system is good, and does not know of a better
system. “But, I am still wondering if it is adequate to base
earn-a-buck on, and he did find some discrepancies there,” he
Tim Van Deelen, professor of wildlife ecology at UW-Madison who
served as an intermediary with the committee and the DNR, said he
thought the report was a “very impressive piece of work and
involved one of the most rigorous population estimates” he had
Warnke said that if wildlife management were to put a list of
the top 10 outstanding experts in the United States, it would have
included the six people on the panel.
Others on the panel included Josh Millspaugh, University of
Missouri; Duane Diefenbach, Pennsylvania Cooperative Fisha dn
Wildlife Research Unit; Lonnie Hansen, Missouri Department of
Conservation; Kent Kammermeyer, Georgia DNR; and John Skalski,
University of Washington.
“We’ll take these recommendations seriously and see how we can
implement them,” he said.
The steering committee will now study the draft report and go
back to their respective organizations and provide Van Deelen with
their questions. Van Deelen will send the questions to the panel,
which will then be connected on a conference call on Jan. 3 with
steering committee members.
The steering committee will write a report to the Natural
Resources Board; the report will be attached to the final report by
the expert panel and presented to the NRB at its January