Bear decline in Chippewa National Forest brings out DNR researchers

Post date: Aug 23, 2016 3:15:58 PM

Migration, breeding and habitat are among factors examined in project.

By JOE ALBERT Special to the Star Tribune

August 20, 2016 — 5:41pm

Department of Natural Resources - A black bear in a northern Minnesota area being studied by the DNR hovered over a baited trap. Researchers hoped to catch the animal and fit it with a tracking collar.

The Department of Natural Resources in recent years has been tightfisted with the number of bear-hunting permits it’s given out, in an attempt to increase the size of Minnesota’s black bear population.

Though the agency offered slightly more permits this year — 3,850 — it’s still a fraction of the number available a decade ago. Still, when the bear-hunting season opens Sept. 1, state wildlife officials believe hunters will be targeting a growing bear population.

“At least judging by the nuisance complaints, there seems to be more bears out there,” said Perry Loegering, the DNR’s Grand Rapids-area wildlife manager.

But in a heavily studied area comprising the Chippewa National Forest north of Grand Rapids — thought to be representative of the state’s bear range — a precipitous decline in the population has researchers trying to figure out what’s going on. There, DNR bear researchers Dave Garshelis and Andrew Tri, along with U graduate student Spencer Rettler are working to determine why the bruin population is half or less what it was during the 1980s.

Foundational study

DNR researchers in 1981 began collaring black bears with VHF collars within the Chippewa National Forest. In addition to its proximity to the agency’s forest wildlife research office, the study area also was “dead center of the bear range,” Garshelis said. Researchers aimed to learn about bear movement and habitat use, as well as mortality and reproduction. At the time, it had been only a few years since bears were considered varmints and bounties were given for them.

Throughout the 1980s, researchers trapped bears, fitted them with collars and ear tags, and collected data related to their body condition. They also visited bear dens when they were hibernating and fitted cubs with collars and ear tags. Researchers collared more than 300 bears, and tracked 290 until the animals died.

It became evident early on bears aren’t exactly homebodies, making annual late-summer or fall migrations. Males, for example, would head 50 miles south from their summer range and then turn around and walk 100 miles to the north, where they’d spend the winter. Female bears made similar movements but covered shorter distances. “They definitely move consistently southward, and they go to places where there is better food — richer soils, more oaks, and also more agriculture,” Garshelis said.

Researchers also learned that many females had three-cub litters — rather than two, as commonly had been believed — and that they tended to have more male than female cubs. However, male cubs died at a faster rate than female cubs, so the male-to-female ratio largely evened out by the end of the cubs’ first year.

Researchers also learned that hunting was the main source of bear mortality. Of the 290 bears, hunters killed 235. Some were killed when they became nuisances, while vehicles hit others. Eight died of natural causes. “It’s not like deer, where you can have a bad winter and a bunch of deer die,” Garshelis said. “If you cut back hunting enough, the population will go up.”

Moving on

By the early 1990s, researchers believed they had a good handle on the bear population in the study area, having collared about 90 percent of the animals living there. While they continued to track collared animals — including one that lived to nearly 40 years old — they largely turned their attention elsewhere.

But Garshelis didn’t forget about that original study site, and decided to revisit it in 2012. “Our concern was that we had pretty good evidence that we had a declining statewide bear population,” he said. “We thought it would be good to see — since we had such great data on this study area — how it had changed.”

That meant stringing barbed wire and placing baits in each section within the 120-square-mile study area. As bears attempted to get to the baits, they’d go over or under the barbed wire, which would pull off a chunk of hair. Via DNA analysis of the hair, which allowed them to identify individual bears, researchers determined the density in the study area was about one bear per 7 square miles. In the late 1980s, in “exactly the same area,” the density estimate was one bear every 2 square miles, Garshelis said.

“We had purposely wanted to reduce the population, but probably not that much,” he said.

Back to the Chippewa

Sufficiently concerned, the DNR decided to conduct another study in the area. The objectives: determine why the home ranges of bears within the area had increased to the extent they did, and why the bear density had fallen. In 2015, Rettler, the graduate student, surveyed the food resources in the area. This year, the food part of the study continues, and 18 bears have been fitted with GPS collars.

It’s possible hunting pressure is solely responsible for the decline, but Garshelis cited habitat that he believes has become less productive since the 1980s. Researchers already can see berry production is lower than in the 1980s, and U.S. Forest Service forest inventory assessments also paint a picture of how the forest has changed. In the 1980s, there were young stands of aspen and red pines, which were highly productive in terms of bear food. Those trees have matured and don’t provide the food they once did. “The other major thing that’s happened is there’s a lot more mature maple trees, which is the least productive forest type for bears. There’s very little that grows under a maple,” Garshelis said. “These changes suggest there’s less food abundance for bears.”