The world's oldest known wild bear — a 39½-year-old black bear that has roamed the woods near the Bigfork-Marcell area of northern Minnesota — might be running out of time and luck.

The elderly female bruin, simply called No. 56 because of the numbered tag she was given when radio-collared by researchers in 1981 at age 7, has trouble hearing and seeing and navigating the thick woods. So the bear is using roads and trails, and is more frequently encountering area residents.

Because of those factors, researchers say she is now more vulnerable to being hit by a car or shot as a nuisance bear or by hunters — and they are asking residents for patience.

They would like No. 56 to die of natural causes.

"We've never seen a wild bear die of old age,'' said Karen Noyce, Department of Natural Resources research biologist in Grand Rapids who has been monitoring No. 56 since she first tranquilized and attached a radio ­collar to the bear 32 years ago. "It's just extremely rare. We're not going to crack any secrets, but it's so rare to get an opportunity to watch a wild animal age normally.

"We're trying to get the word out to everyone in that area. A lot of people already know about her.''

Jayson Hansen, DNR conservation officer in Bigfork, said people are seeing the bear on roads and sometimes near their homes. "She's been sighted numerous times this spring,'' he said. He asked residents to treat the bear with respect, and said it likely will run off once it senses a human.

How rare is a 39-year-old black bear?

• The average age of a bear killed by a Minnesota hunter is less than 4 years old.

• About 80 percent of No. 56's estimated 26 cubs died by age 6. (She last gave birth at age 26.)

• Of the hundreds of bears that have been radio-collared and studied by the DNR over the past 32 years, the longest any survived was 23 years.

"Some bears in zoos have made it into their 40s,'' Noyce said. "But in terms of a wild bear, one whose age has been documented and studied, no one has had a study bear over age 35.''

Bear isn't drunk

Noyce and other researchers have located No. 56 every three years to tranquilize her and attach a new radio-collar. They last did that in 2010, but Noyce recently used the radio-tracking device to find the bear to see how she was doing.

"She doesn't hear much, and can't see much,'' Noyce said. "I got to within about 10 feet from her, downwind, and she was sound asleep. I moved upwind of her, about 20 feet away, and she immediately got up and made a beeline away from me. She was definitely aware of me.''

Added Noyce: "Her gait is a little unsteady. When people see her they think she looks drunk. That's because no one ever sees an old, old, old bear like that. But she doesn't seem to be in any pain.

"Her teeth have been terrible for six years, but she still has teeth,'' Noyce said. The bear was nearly 200 pounds when last weighed three years ago. "She's thin now,'' Noyce said.

Though the bear's days are numbered, Noyce said she has no idea how long the old gal might live, adding: "I can't predict. She could lie down and die tomorrow, or keep going.''

But residents shouldn't assume the old bear is safe to approach just because it doesn't run off as younger bears usually do.

"She's not a tame bear,'' Noyce said. "People shouldn't approach her.'' The bear's first reaction — like other black bears — is to run away from humans. But if she's cornered or startled, she could defend herself.

Why a long life?

Noyce believes No. 56's unprecedented longevity is more than luck — perhaps a stronger-than-normal ­wariness of humans.

"She lives in an area with a fair amount of room and few roads, and she hasn't been prone to come to houses as a nuisance bear, or to ­hunters' bait,'' Noyce said. "That's what's changed recently. Suddenly in the last couple years she's been seen a lot, because clearly she's not able to navigate in the woods as well.''

The bear has feasted at hunters' bait sites in recent years, but hunters have honored the DNR's request to let her live. (Shooting radio-collared research bears isn't illegal, but the DNR asks hunters to avoid shooting them.)

"Most hunters up here know about her," Hansen said. The bear has attained something of a legendary ­status. "Everyone seems to brag when she comes into their bait,'' he said.

No. 56 isn't a large trophy bear, and 39-year-old bear meat isn't appetizing.

"The meat wouldn't be something I'd want to put on my dinner table,'' Hansen said.

Minnesota's bear season runs Sept. 1 to Oct. 13.

Noyce said the old bear is hard to miss: She has a large radio collar with blaze-orange tape around her neck, and orange and yellow ear tags.

More than just a bear

Noyce plans to check on No. 56 every couple of weeks. The bear's special collar will indicate if she stops moving, meaning she likely is dead.

Noyce is prepared for that.

"We try not to become attached to our study animals," she said. "We see animals born and dying all the time. That's just part of the job. But I admit to having a great fondness for this bear. I feel really privileged to have watched her all these years.

"It will be sad when she dies, but the best outcome would be if she doesn't wake up from an afternoon nap and dies a natural death from old age."

Doug Smith •