Tetracycline pills will help DNR pinpoint bear numbers
By Larry Polenske Correspondent
Madison — Beginning this summer, Wisconsin black bears will eat
tetracycline pills that should give researchers a clearer picture
of the bear population down the road when they look at bear bones
or teeth for “stains.”
If this new plan helps biologists get the dart closer to the
bull’s-eye on bear numbers, bear hunters could benefit. Some
hunters say the DNR is underestimating the bear population and
should be issuing more permits. If the study bears out that theory,
then the DNR would increase permit numbers, according to DNR Bear
Ecologist Keith Warnke.
It also could work in reverse, if the tetracycline tablet study
shows that numbers are lower than estimated.
The DNR estimates bear numbers at 10,950 animals. Many bear
hunters and the Conservation Congress Bear Study Committee believe
that, based on field observations, that number is way too low. Some
residents in bear country that have experienced crop or property
damage from bears agree. Warnke said that he gets calls from people
who think the DNR bear estimate is low.
However, he said he also gets calls from people who say the
number is too high, and calls from people who say it is right on
The Wisconsin Bear Hunters Association (WBHA), the DNR, and
wildlife researchers from UW-Madison are collaborating on a plan
either to reinforce the DNR’s estimate, or find a way to make it
If study results do indeed show a higher population than the
present estimate, it would reduce the time it takes to draw a kill
Warnke said it takes about six or seven years to get a bear kill
tag for Zone A or Zone A1. Hunters in Zone B can wait up to nine
years; Zone C five to six years.
Mike Gappa, of Eau Claire, is the retired DNR “bear guy.” When
Gappa retired, the WBHA put him back to work as the group’s bear
biologist, and Gappa is one of the lead researchers on the
“This is the biggest ‘mark and recapture’ study that Wisconsin
has ever done on bear,” Gappa said.
The tetracycline will “mark” bears by staining the bones and
teeth of bears that eat tetracycline tablets. The “recapture” will
come when hunters kill a bear during hunting season. Biologists
then will compare the number of “marked” bears to bears with clean
The idea is very similar to the way the DNR fishery crews make
fish population estimates by comparing fin-clipped fish to “clean”
The DNR has approved all of the permits, funding and biologists
to assist in coordinating and interpreting data from the study. The
DNR also has a role in working with the public and bordering states
to ensure cooperation on the project.
Gappa said Wisconsin’s bear population model is regarded as one
of the best in the nation.
“This survey will help us refine that model to indicate whether
or not we are on line, or we are too conservative, or we are too
aggressive in our harvest,” he said.
Several inputs are used in the population model. One is the
yearly bear harvest and the sex of those animals. Another input is
the age of those bears. A baiting transect survey also is used in
the model. Every year baits are put out at half-mile intervals
along 25-mile-long transects in 18 locations in Wisconsin’s bear
range. The difference in the number of baits hit each year can
indicate changes in the bear population. Reproduction rates and
natural mortality also are part of the equation.
Gappa said this new mark and recapture study will involve
putting out about 3,700 bait boxes in random areas three to four
miles apart in primary and secondary bear range. This study will
cover more ground than the DNR’s annual transect routes. Each box
will contain bacon laced with nine tetracycline pills. Bacon cannot
be used as bait for hunting, but the DNR has allowed it for this
project. The boxes will be mounted at least six feet off the ground
to prevent ground predators from eating the bait. The box will be
strong enough to keep out raccoons and fishers, but a bear will
have no trouble getting to the bacon.
The WBHA hopes to have all the boxes in place by July 1. Each is
marked clearly to indicate it is the property of the WBHA and UW.
Anyone who comes across a box is asked to leave it alone. The boxes
will remain in the woods until a bear hits them, but all will be
removed by Aug. 13, before the bear season opens.
The tetracycline used in the study is a veterinarian grade
antibiotic. It will leave a marker, or stain, in a bear’s bone
structure, but does not harm the animals. Humans have no risk in
eating meat from a bear that has consumed tetracycline.
Bear hunters have an important role in this study. Warnke said
for the next two years successful bear hunters would be required to
submit a small rib sample from their bears for analysis. Hunters
are already required to submit a tooth sample. Warnke said the DNR
never gets total compliance with something like this, but he is
confident that a vast majority of hunters will cooperate. There
will be additional information on rib submission through press
releases and at registration stations.
UW-Madison wildlife ecology professor Tim Van Deelen oversees
the university’s role in the project. Dave Macfarland, one of his
students, is the primary researcher. Macfarland, a Massachusetts
native, is working on his Ph.D. in wildlife ecology. Van Deelen and
Macfarland are consulting with, and coordinating, volunteers for
the project. They also will assist in data analysis.
When the study concludes, Macfarland said three numbers will be
established: the total number of baits that were hit, the total
number of bears that were harvested, and the number of
tetracycline-marked bears that were part of the overall kill. From
those numbers an estimate can be made of the total bear
Macfarland said a simplified example would use 100 as the number
of bears marked. If the total bear kill was 500, and 50 of the
harvested bears were marked with tetracycline, it could be assumed
that 10 percent of all bears were marked. That would result in a
population estimate of 1,000 total bears. There are other variables
to be considered, and these numbers are not close to the actual
bear population or harvest.
This type of study is based on principals that have been used on
other types of game and have been used on bears in Michigan and
Minnesota. Macfarland said they are modifying and improving
techniques used in past studies to make this project as accurate as
The WBHA is supplying funds and thousands of man hours to the
project. Members are responsible for hanging the baits and for
building the boxes. A group of carpenters in Neillsville built
about 2,500 boxes. West Bend’s Chucker Dreher contacted the
Kewaskum Middle School in Washington County for help. Shop students
there built about 1,200 boxes.
Preliminary results will be available after the 2006 hunting
season, but no conclusions will be made until some time after the
Warnke said if data from the project show there are more bears
on a statewide basis, the number of kill permits could be increased
within a couple seasons after completion of the study.
Macfarland said the study also will provide data on habitat
modeling. This will be useful in predicting where the bear
population is likely to grow. The habitat data might provide
insight on reducing future conflicts with agriculture and nuisance
reports of bears in backyards.