DNR Division of Fish and Wildlife - Summer 1997
Dental detectives determining state's black bear populations
3,000 bags of antibiotic-laced bacon are key to an innovative technique to survey Minnesota's black bear population
Wildlife research biologists are literally "bringing home the bacon" this summer as they undertake a major study to determine the number of bears living in central and northern Minnesota forests.
The study involves hanging several bags of bacon in every township in the state's bear range. Each bag contains nine capsules of tetracycline, an antibiotic used to treat both people and livestock. Tetracycline is incorporated into any newly forming tooth or bone material after being ingested by the animal. This later shows up as a fluorescent mark when the bone or tooth is examined under ultraviolet light.
"We first used this technique in 1991 to obtain an estimate of bear numbers," says Karen Noyce, DNR wildlife research specialist at Grand Rapids. "Based on that survey, we concluded that roughly 14,000 to 17,000 bears inhabited Minnesota."
That population range compared well to estimates from a mathematical population model, which Noyce and other bear researchers use each year to predict changes in bear numbers. Noyce says that while the model currently suggests the population has grown to about 20,000, "it's time to once again check its predictions against an estimate obtained from the tetracycline survey."
Hunters who harvest bears this autumn will be asked to provide the DNR with a tooth and a small piece of rib bone from near the animal's spine. From these samples, the wildlife researchers will determine the percentage of bears that ate tetracycline-laced bait. They'll divide this number into the number of baits eaten to estimate the total statewide population.
Earlier this summer, roughly 3,000 bags of bacon were hung in trees every 3 or so miles. Wildlife biologists and technicians are currently checking each bait site to see how many have been eaten by bears. Bacon bags are hung high on smooth-barked trees that show claw marks, which are then measured to figure out whether the scavenger was a bear, raccoon, fisher, or other bacon fancier.
Determining the state's bear population is important for two main reasons. First, the number of bear hunting permits that are issued each year is based on the number of bears estimated in each management zone. Second, an accurate population figure is needed from time to time to ensure that the computer model is on track in projecting annual populations.