February 01, 2015

Michigan’s black bear population is healthy, not declining, according to the most recent estimate made public at the Bear Symposium hosted by the DNR at Roscommon’s RAM Center on December 6. So the reduction in the number of bear licenses issued in the state over the last three years was not necessary. The reduced bear harvest that occurred over those years will insure the population is increasing, however, which is a good thing.

A new technique was used to come up with the most recent bear population estimate. It’s called statistical reconstruction and it was explained by DNR research specialist Sarah Mayhew at the Bear Symposium.

“We have sex and age data from our bear population since 1992 to the present,” Mayhew said. “We have the age at harvest for our bears from mandatory registration of animals taken by hunters. Those ages are determined by looking at the teeth from those bears. Hunting effort is determined by annual surveys of bear hunters.

“All of the information is plugged into the program and it goes through a number of scenarios to determine what the bear population was most likely to have been like to produce the harvest that we know we had, given the other data that is known.”

Susan Smith from Kawkawlin with a black bear she bagged in Dickinson County on September 15 that had a live weight of 410 pounds.

Based on the statistical reconstruction of Michigan’s bear population, Mayhew said there were an estimated 11,000 bears that were more than a year old in the areas open to bear hunting on September 9, 2014. She said 9,000 of them were in the UP and 2,000 in the Lower Peninsula.

“Based on the data, the bear population in the UP has been stable for about the last 20 years,” Mayhew said. “Those figures only include bears that are at least a year old before bear season begins. They do not include cubs.

“Since females with cubs are protected during hunting season, there has been a gradual increase in the number of reproductive females in the population and there has also been a gradual increase in the average number of cubs per female,” Mayhew commented. “Females of reproductive age only have cubs every other year. If you average out the number of cubs produced per year for all females, it is 1.2. If you only consider reproductive females, meaning those that had cubs that year, the number of cubs per female is about 2.5.”

Productive females can have as many as five cubs, but four cubs are more common. Some females such as first time mothers only give birth to one cub, however. Mayhew did not have an estimate of the number of reproductive females that there would be in the state for any particular year.

If one third or 3,630 members of the bear population were reproductive females, however, they would produce 9,075 cubs. That would put the state bear population at about 20,000. Not all cubs survive their first year of life though. Cub mortality varies by region, being the highest in portions of the UP where wolves prey on cubs.

Mayhew added that by using this new method of estimating the bear population, the DNR can produce an annual estimate after the new data gathered each year is plugged into it, that is cheaper and less labor intensive than previous methods. In the past, tetracycline baits have been used to estimate bear numbers in the UP and DNA analysis of bear hair collected from baited snares has been used in the northern Lower Peninsula. Both of these methods are labor intensive and costly.

In the UP, tetracycline capsules are wrapped in bacon for bait and they are hung from trees to increase the chances that bears will eat them. The tetracycline stains the teeth of bears and those that have been marked in this fashion can be detected when the teeth of harvested bears are examined. Hundreds of these baits are put out across the UP each time this type of marking effort is done.

Then biologists have to revisit the baits to determine which ones have been eaten by bears. For accuracy, it is important for researchers to be able to differentiate baits eaten by bears and nontarget animals such as fisher and raccoons. To aid in determining what animal ate baits during 2014, game cameras were placed to monitor 97 baits.

Setting up baited hair snares at a number of locations in the Lower Peninsula and collecting hair samples from them is also labor intensive. Then DNA information has to be extracted from those samples and analyzed.

Bear population estimates for the UP based on tetracycline baits conducted previously were what led wildlife biologists to think bear numbers were declining there, which led to a 32% reduction in the number of bear licenses issued for the UP from 2012 through 2014. Those estimates were inaccurate based on the more recent statistical reconstruction method.

“All methods used to estimate populations are subject to errors,” DNR wildlife researcher Dwayne Etter said. “That was the best available information at the time. We now recognize we have problems with the tetracycline capsules used in baits. The capsules are thinner than they used to be. When we wrapped them in bacon this year, the moisture from the bacon dissolved the capsules, making the baits less appealing to bears. That might be responsible for fewer baits taken by bears than fewer bears being present.

“The statistical reconstruction of our bear population that Sarah did is now the best scientific data available about Michigan bear numbers. These numbers only apply on a regional basis. It isn’t detailed enough to provide estimates on a local or county level.”

Some hunters who questioned the new population estimates felt that there are fewer older female black bears in the population to produce cubs, suggesting most of the females are young animals. Mayhew produced a graph showing the ages of females harvested by hunters over a period of years that showed there are just as many old females being harvested by hunters in the state during recent yeas as there were in the past. In fact, Etter said the age distribution of females in the harvest has been fairly constant for many years.

The majority of the bears bagged by hunters annually continue to be males. More than 60% of the bears taken by hunters are males.