Mystery around bears' reproduction is a reminder of their balancing act

Minnesota over the years hasn't been quite sure what to do with its bears. Early settlers feared them or killed them for food, and from 1945 to 1965 the state paid $10 bounties to people who dispatched bruins that toppled garbage cans, broke into cabins or otherwise made nuisances of themselves.

Considered vermin, bears decades ago were sometimes gut-shot by Minnesota deer hunters who watched the animals run off to die in distant locations.

All of which began to change when the state declared the black bear a game animal and held its first hunting season for bruins in 1971. That designation polished the animal's image, set in motion its formal management and initiated world-class research by Department of Natural Resources (DNR) staff in the agency's Grand Rapids office.

Bear research is important in part because female bruins begin reproducing at older ages than most other large mammals. Also, bears can be vulnerable to overharvest if they are tempted too often to visit hunters' baits when wild berries and other natural-food crops are in short supply.

In the 1970s the DNR issued bear-hunting permits to anyone who applied. Beginning in the early 1980s, wildlife managers limited by quota the number of permits issued, assigning them by lottery. Bear numbers subsequently more than doubled to as high as 20,000 by the late 1990s.

But nuisance complaints also increased, and partly in response, permit quotas were relaxed. By 2013, the state's bear population had dropped by more than half. Along with hunting, which is the primary contributor to bear mortality in Minnesota, statewide failures of dogwood, hazelnut, highbush cranberry, acorns and other berries in 1995 and 2001 contributed to the precipitous decline.

In the years since, wildlife managers have attempted to achieve a delicate balancing act. They want to minimize nuisance-bear complaints while satisfying hunters' desires to pursue what has become a prestigious Minnesota game animal, while also, most important, maintaining a healthy, stable bruin population.

The latest DNR estimate places the state's bear population at between 12,000 and 15,000.

Until he retired in December after 37 years with the DNR, Dave Garshelis was the agency's lead bear researcher. His work, along with that of colleagues Pam Coy, Karen Noyce (who retired in 2014) and others, as well as Garshelis' successor, acting DNR lead bear researcher Andy Tri, is unrivaled in North America.

Yet bears remain mysterious critters, as Tri and his colleagues were reminded anew recently when they discovered the age at which female bears along the edges of their Minnesota range are beginning to reproduce at older ages than has historically been the case.

In the state's "core" bear range, the age of initial reproduction, or "primiparity," of female black bears, is 5, except in the Boundary Waters Canoe Area Wilderness, where the age is 6.

On the edges of this region, oaks and their highly nutritious acorns are more abundant, as are farmers' corn and other fields. Here the average age at which sow bears have their first cubs typically has been closer to age 4.

The difference is significant, Tri said, and could cause the area's already tightly controlled number of bear-hunting permits to be restricted even further.

"If reproduction is suffering, and we believe it is among bears in this periphery region, food availability could be the reason, or there could be an external reason we don't yet understand," Tri said. "We're hypothesizing, but perhaps it's an increased use of pesticides, as farmers in the region are more often planting from forest edge to forest edge. Or perhaps it's a bear health issue, though generally bears are very robust critters."

The reproductive age difference was discovered by researchers studying the teeth of female bears killed by hunters dating to the 1970s. "Rings" in the teeth, or bands, designate a bear's age. The width of a sow's rings, meanwhile, shows the years she had cubs.

"Thin bands, or rings, show she had cubs that year, while wider bands were years she had yearlings with her or no offspring," Tri said. "Female bears expend considerable energy providing milk for their cubs, especially while hibernating, and the thinner bands in her teeth illustrate this."

Other factors also are affecting bears in northern Minnesota and contribute to the DNR's management challenges.

One is the 50% decline in berries Tri's research group has documented in the Chippewa National Forest. "In the 1980s," he said, "we could walk five stands of forest and find berries in four of them. Now it's two out of five."

Last year, Tri said, was one of Minnesota's worst berry years on record. As a result, bears in the state's core range are traveling farther than ever to find food, and they're visiting hunters' evermore palatable baits with increased frequency.

"Fully 90 percent of our radio-collared study bears hit hunters' baits last year," Tri said. "Which is OK as long as most of the bears hit the baits at night and don't get shot."

But a lot of bears did fall to hunters in 2020. In the state's bear-hunting-permit "quota" area, 57% of hunters were successful. In the "no-quota" area, 37% of hunters bagged bears.

Both were records and will factor into the number of hunting permits the DNR issues this fall.

"The state's bear population is stable," Tri said, "but we're hoping to increase it so bears can better withstand the bad food years that occur periodically."