Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Photo of a black bear © Herb Lange

Working together for the conservation of Wisconsin's black bears.
© Herb Lange

December 2011

Count on it

A bear population estimate based on bait and bones.

Dave Wilson

It seemed to be a daunting task. I imagined plowing through an alder swamp and flooded bottomlands mired in mud. How, I wondered, could the Wisconsin Department of Natural Resources possibly count black bears in such wild places as Price County's Million Acre Swamp or Bayfield County's Bibon Marsh? I decided to find out for myself by volunteering for Wisconsin's black bear survey. What I discovered, is that the way the Department of Natural Resources counts bears is nothing like the way the United States Census Bureau counts U.S. citizens.

I was grateful. I couldn't imagine trying to burrow through the Million Acre Swamp with a notebook and pencil, knocking on bear dens and trying to count boars, sows and cubs.

The new and more accurate method to estimate the state's bear population relies on bears ingesting tetracycline (a biomarker). Bear hunters then sample harvested bear rib bones to detect the presence of the compound.

Currently, all DNR bear research and management activities are directed towards managing bear populations within zones and developing harvest strategies to maintain populations at or near prescribed goals. Population goals for each zone are based on habitat suitability and human tolerance levels.

Tetracycline surveys have been used to estimate black bear populations in Minnesota and Michigan since the mid 1990s. Their success led the Wisconsin Department of Natural Resources to explore using this technique here. Research Scientist David MacFarland, in cooperation with the Wisconsin Bear Hunters Association and the Department of Natural Resources, conducted the first Wisconsin tetracycline study from 2006 to 2008. The study found the black bear population to be almost twice as large as previously estimated with the population model survey. The Department of Natural Resources adopted this technique and paid for the first study.

The tetracyline survey involves placing four bait boxes in each township in all counties within the black bear range. The bait packages contain tetracycline capsules embedded in peanut butter and marshmallows. During the bear hunt, successful hunters submit a bear tooth and a two-inch piece of bear rib collected near the vertebrae at the time of registration.

The tetracycline study uses mark-recapture, a well-established tool for estimating wildlife populations, and is similar to duck banding. The technique relies upon two encounters with an animal: the first marks the animal, the second checks for the mark. A population estimate is derived by knowing the number of animals marked and the proportion of marked animals in the second group. For example, if we marked 100 animals in the first group, checked 100 animals in the second, 10 of which (or 10 percent) were marked, we would know that the initial group of 100 represented 10 percent of the total population resulting in an estimate of 1,000 animals.

Black bear tetracycline abundance estimation study area, 2011

Map of Wisconsin showing sampled area and non-sampled area © DNR File

"In this study we mark bears with tetracycline which is visible in bone tissue," MacFarland explains. "The annual harvest gives us an opportunity to check for marks in hunter-submitted bear rib samples. We can then calculate what percent of bears were marked with tetracycline and use that information to estimate the total population size." In the autumn of 2006 the Department of Natural Resources estimated 33,657 bears, plus or minus 7,042, older than one year in Wisconsin. Estimates for the current survey will follow in an upcoming Wisconsin Natural Resources magazine issue.

Establishing the bait locations

When I volunteered to help with the bear tetracycline survey, I requested to work near where I live. Surveyors assigned volunteers at random to ensure that the baits were located far enough away from each other so the same bear would probably not hit two baits. Price County has 38 townships and had 152 bait boxes placed for this survey. I recorded the GPS coordinates of all my assigned bait locations.

We needed to place the baits seven to eight feet off the ground, preferably in a tree that would support a bear. The tree would also ideally have smooth bark so we could easily see and identify claw marks.

Bait #1

I placed the first bait on the river bottom in an area where I used to bow hunt, in the Price County forest on the South Fork of the Flambeau River. I knew that bears traveled through this area; in fact, a cub climbed the same tree that I was hunting from several years ago.

Bait #2

I placed the second bait on private land about four miles south of the first bait. I called the owner ahead of time to let him know I was coming. The area biologist had previously secured permission for me to place the bait. I placed the bait in open hardwoods. The landowner said he had seen a bear on his land a few days earlier.

Bait #3

I placed the third bait on land owned by Northern States Power Company. The area is high ground with mixed hardwoods and conifers. This bait was approximately four to five miles east of the second bait.

Bait #4

The private land where I placed the fourth bait was in an old clear-cut next to the Million Acre Swamp. I know bears favor this kind of habitat. I nailed this bait box to an aspen tree about six inches in diameter. This bait was four to five miles north of the third bait.

If a person looked on a map of the Town of Flambeau, the baits appear in a rough square running four to five miles to a side.


More than 600 volunteers and DNR staff deployed and monitored 3,317 baits across 32 counties last spring, 940 of which were consumed by bears. The Wisconsin Bear Hunters Association donated the bait boxes, which stayed in place for at least two weeks and no more than three weeks.

Photo of claw marks on tree bark © DNR File
This tree shows signs that it was visited by a bear.
© DNR File

Two of "my" baits were located in open hardwoods. I was not surprised that bears, because of the open habitat, did not visit them. The other two were in low areas – one on a river bottom and the other on the edge of a large swamp. I expected those would be hit but they were not. I returned all the bait boxes to the DNR station in Park Falls. I also removed all the nails used to secure the bait box in the tree and properly disposed of them.

And even though my bait boxes weren't hit, I saw a sow and two cubs on the way home from work the Saturday night before I picked up the bait boxes, and several bears checked out my garbage the night after I picked up the boxes.

The Department of Natural Resources also reported that prospects were good for the 2011 Wisconsin black bear hunting season that opened September 7, and that bears are thriving and continuing to explore new territories in Wisconsin.

The DNR issued around 9,000 permits for the 2011 fall season, which ran through October 11, and the statewide harvest quota was 5,235 bear, the same as in 2010.

"Excitement is high among the bear hunters I have spoken with," said Linda Olver, bear biologist with the Department of Natural Resources, at the start of the fall hunt. "Many have submitted trail camera photos of bear visiting their baiting sites and there are some pretty impressive bear out there. Whether or not we have a season like 2010, when a new bear harvest record was set and at least three 700-pound bears were registered, remains to be seen but the potential is there."

Bear or no bear, I enjoyed volunteering for the bear survey. I got out in the woods during a beautiful time of the year just ahead of the leaves and mosquitoes. I met some new people in the township where I live, and I came to understand and appreciate the difficulty of how bear populations are estimated in Wisconsin, both with the newer tetracycline method and with the existing population model.

"This research is a great example of what a partnership can accomplish," says Tom Hauge, director of the DNR Bureau of Wildlife Management. "The project and population estimate simply wouldn't have been possible without DNR staff, the Wisconsin Bear Hunters Association and the committed volunteers working together for the conservation of Wisconsin's black bears."

Dave Wilson lives off the grid in a log cabin he built on the South Fork of the Flambeau.