Crisp wind, falling leaves, shorter days, cooler nights — something in the fall triggers the black bear to pick up the pace and eat.

Eat before winter comes.

Eat before it’s too late.

Biologists call this period of escalated foraging “hyperphagia.”

“There’s almost a desperation,” said Randy Cross, state wildlife biologist and leader of Maine’s black bear monitoring program. “The bear is driven to go for high calories — to lay on a lot of fat. That’s what they’re trying to do every day, all summer long, but in the fall, it’s critical.”

While in hyperphagia, black bears are capable of foraging up to 23 hours a day, Cross said. And to pack on the pounds, they consume a wide variety of food, from leafy greens to fresh roadkill, from berries to bees.

To describe a black bear’s diet, Cross quoted the famous American naturalist John Muir, who said, for a grizzly, “almost everything is food except granite.”

“While this may have been a slight exaggeration, it is remarkably close to the truth,” Cross said. “And black bears may be substituted for grizzlies here without affecting its accuracy.”

Nevertheless, there are a few foods black bears prefer.

Berries. Strawberries, blueberries, blackberries, raspberries, cranberries — black bears love them all. And this year, after a wet spring and summer, Cross predicts there will be plenty of berries to go around.

Another key calorie source in the fall is nuts, which are falling to the ground, ready to be consumed — though bears will certainly clamber up trees to retrieve any that have yet to fall.

“Sometimes, bears will travel great distances in search of some really good food; typically, it’s acorns or beechnuts,” said state wildlife biologist Jennifer Vashon, who has been in charge of  both Maine’s Black Bear and lynx programs since 2002.

Insects serve as another important source of protein, more specifically, colonial insects such as ants, bees and wasps.

Why? Bears are out to get the most bang for their buck. Colonial insects live together, so all a bear has to do is find one home — one anthill or beehive — and he uncovers a feast.

“Bears are very finely tuned machines when it comes to foraging,” Cross said.

Furthermore, bears seem to wait to break into a hive until the protein-rich larvae are growing inside.

“The bears know when that is,” Cross said. “And they seem to know it by smell.”

“Beekeepers obviously have trouble with bears,” he continued. “Bears get into bees. It’s just what bears do.”

In fact, bears are fairly “bee-proof,” according to Cross. Their thick coat protects their bodies from being stung, though they do suffer stings on their lips, nose and around their eyes.

“It does bother them — at least, it appears to, watching them get stung as they raid a beehive —  they shake their heads a lot,” Cross said. “But, and this is a big but, they are a lot tougher than you or me, and the reward is worth the temporary discomfort.”

Yet human-bear conflicts rarely increase during the bears’ fall foraging frenzy, according to both Cross and Vashon. Fall is a time when natural food is abundant, and that’s usually what bears are going after.

(Human-bear conflicts are actually more common in the spring, when a bear has just emerged from its den and is searching for sustenance when natural food is scarce.)

Still, a few conflicts do happen. Bears are opportunistic. They’ll raid sweet corn from someone’s backyard garden and pilfer leftovers from the trash.

“The number one issue is birdfeeders — as soon as a bear finds it, it’s a bear feeder,” Cross said.

“Most conflicts happen where people aren’t used to having bears around,” Cross said. “Up in northern Maine, a lot of people gave up on feeding birds years ago. But there’s no place in Maine where you’re perfectly safe from bears. They live throughout the state.”

Still, Maine’s estimated 31,000 black bears keep to themselves, if they can help it. And upon seeing a human, they typically will run in the opposite direction.

“The only problem is when a bear is cornered. I think that’s when you’re at the greatest risk — If you’re between a bear and cubs or between a bear and its escape route,” Vashon said. “A good example is if you find a bear in your garage and you’re blocking the door.”

As frost sets into the ground, Maine people will be less likely to spy a black bear, though Cross predicts that bears will hold out longer before denning up this year because of the abundant fall foods.

“Bears don’t go by the calendar,” he said. “As soon as [a bear is] losing more energy than it’s gaining, its body recognizes that and flips a switch and says, ‘Stop moving. You’re wasting energy.’”

Then, on the cusp of winter, the black bear retreats into its den — a hollow log, cave or some other natural cavity — and essentially dozes all winter long. The bear is inactive yet conscious enough to remain aware of danger.

Snow piles up outside the den. Lakes and ponds freeze. Months pass. And all this time, the bear has not a bite to eat. And that is why the black bear takes full advantage of his last meal of the year — a meal that lasts for days but sustains him for months.

Aislinn Sarnacki

Aislinn Sarnacki is a Maine outdoors writer and the author of three Maine hiking guidebooks including “Family Friendly Hikes in Maine.” Find her on Twitter and Facebook @1minhikegirl. You can also...