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 money.
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 more accurate.
If study results do indeed show a higher population than the present estimate, it would reduce the time it takes to draw a kill tag.
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 project.
“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 bones.
The idea is very similar to the way the DNR fishery crews make fish population estimates by comparing fin-clipped fish to “clean” fish.
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 population.
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 possible.
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 2007 season.
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.