Year-Long Insomnia: Why Black Bears Have Stopped Hibernating
Gloria Dickie on the Impact of Climate Change on Bear Behavior in North America
The modern plight of the American black bear starts out much like a joke. Have you heard the one about the bear who walks into the grocery store and grabs a bag of Tostitos? Or, how about the bear who breaks into a gas station and snarfs down a few chocolate bars? Or the bear who binge-eats 24 pounds of pure butter in a confectionary’s kitchen? If you live near Lake Tahoe, you’ve no doubt heard them all—and then some—on the local news.
Lake Tahoe is the cerulean gem shared between California and Nevada. It’s a popular vacation spot for millions, evoking an American nostalgia for the nuclear family getaway when city dwellers would roll up, en masse, with tents and camp stoves to spend five glorious days in the Sierra Nevada. But today, the Lake Tahoe Basin—a textbook example of the wildland-urban interface—is known not just for its azure waters, but as ground zero for black bear-human conflict in the United States.
Motels, mini golf courses, barbecue joints, and blackjack casinos ring the 200-square-mile alpine lake, which serves as a critical water source for the region’s wildlife in times of drought. Once humans began developing its shoreline, resident black bears were given two options—they could either move along or move in. Most chose the latter.Bears had become insomniacs rummaging through the fridge at midnight.
The American black bear is the world’s most bountiful bear and arguably the species that people are most familiar with in their daily lives. If I asked you to picture a bear, you’d probably conjure up images of short black fur, pale snout, a lean build, humpless back, and round ears. Aided by national rewilding efforts over the past century, the black bear has been restored to roughly half of its historical range in the United States. It can be found in the hickory forests of Appalachia; the swamps of Louisiana; the pinyon juniper woodlands of the Southwest; and the palm-fronded Florida Keys.
But black bears can also be found rifling through dumpsters like oversized raccoons and denning under homes in places like Yonkers, New York; Raleigh, North Carolina; and Boston, Massachusetts. Only the Hudson River separates Manhattan from New Jersey’s booming bear population. This sharp increase in black bear numbers combined with rampant human encroachment has given rise to a new breed of bear in America: the urban bear.
At a summer home in Incline Village, on the Nevada side of Lake Tahoe, Carl Lackey was crawling on his hands and knees through a prickly bed of rust-orange pine needles, appearing much like a bear himself. He shone a flashlight into the dark recesses of the crawl space that ran along the house’s foundation. A large male black bear had taken up residence in the owners’ absence and ripped out the fiberglass insulation, dragging in a cache of pine nuts for late-night snacking.
Fortunately—or unfortunately for me—the bear wasn’t home at the moment. “There are tons of sites like this throughout Incline Village,” Lackey said in a gruff tone cultured by the West. He stood up and brushed the clinging needles off his faded blue jeans. “We get a lot of bears here denning underneath homes. Every garbage night they’re out roaming the neighborhoods looking for food.”
Lackey, a biologist with the Nevada Department of Wildlife, was a compact man with a bald head, ginger goatee, and the weathered complexion of a fair-skinned person who had spent a lot of time in the sun. When I’d met him on that drizzly morning in Incline Village, he was driving a truck with two spunky black-and-white Karelian bear dogs named Rooster and Dazzle in the back cab. Karelians—appearing like a cross between a husky and a border collie—originate in northern Europe, where they were used by hunters to chase brown bears.
The fearless dogs have since been popularized by wildlife managers as a tool to scare black bears and grizzlies away from communities in the Mountain West. Lackey was a big proponent of the canine companions, and he’d gotten his first dog, Stryker, from a breeder back in 2001 to respond to the increase in bear incidents around Tahoe. Rooster, the speckled offspring of Stryker, and Dazzle now accompanied him on most of his calls. They’d already chased hundreds of bears away from Nevada’s lakeside towns.
Lackey understood the daily rituals of cosmopolitan bears better than almost anyone else in the American West. He’d been dealing with Tahoe’s urban bears for more than two decades and was one of the first people in America to wise up to the ursine rebellion at the nation’s doorstep. The Lake Tahoe Basin is home to the second-highest density of black bears on the continent, with several bruins roaming nearly every square mile.
So, when American black bears began reclaiming towns and cities, locales near Lake Tahoe experienced some of the largest influxes of migrants. Beginning around 1990, bears that had once spent their entire lives in the wilderness areas surrounding the lake started showing up in Tahoe’s tourist traps, crossing the highway to soak in the lake’s cool waters and tearing into trash cans.
At first, Lackey wasn’t sure what to make of this sudden influx of bears. California and Nevada weren’t in a drought, and the backwoods were full of food. Running through the ecology of American black bears, he and his colleagues concluded that odiferous garbage left unsecured by clueless tourists must be drawing bears out of the wild. Incline Village, on the north shore, was the epicenter.If North America’s bears are hibernating less, they have more time to get into trouble.
At the time of my visit in March, the height of the tourist off-season, Tahoe’s bears should still have been hibernating. Black bears typically don’t emerge from their dens until April, timing their reappearance to match the growth of spring forage. But the urban environment had altered their natural behavior. “Yeah, they’re not really hibernating anymore,” Lackey said nonchalantly as we left the summer house and headed toward the commercial area of Incline Village, skirting the lake and dodging the huge Jeffrey pine cones rolling across the highway. “Instead they’re finding a daybed and coming out once or twice a week.”
Lackey’s throwaway statement took me aback. Bears were no longer hibernating? That seemed like a pretty big deal. Birds fly. Fish swim. And bears hibernate. Under normal circumstances, cold temperatures and reduced natural food availability in early winter send a signal to bears that it’s time to den down. But with a plethora of human food scraps now available year-round, bears had become insomniacs rummaging through the fridge at midnight. In a 2003 study, researchers tracked thirty-eight urban bears around Lake Tahoe and found that while backcountry bears in the nearby Carson Range were entering dens in early December and hibernating as usual, Tahoe’s urban bears were staying up until January. Five of the thirty-eight tracked bears never entered a den at all.
Climate change has compounded this behavioral shift. Warmer winters, later falls, and earlier springs have reset bears’ biological clocks across North America. Some bears no longer hibernate while others are entering the den later or waking up too early. A few winters ago, the National Park Service (NPS) warned visitors at Yellowstone National Park to prepare for possible grizzly bear encounters after above-average February temperatures had grizzlies abandoning their dens weeks ahead of schedule.
A similar pattern was found in black bears by Heather Johnson, a wildlife biologist with the US Geological Survey. She determined that for every 1°C (1.8°F) increase in the minimum winter temperature, black bears living in western Colorado were hibernating for six fewer days. By midcentury, black bears could be awake for an additional two to six weeks.
Johnson told me that although hibernation seems to slow the cellular aging process—apoptosis—in bears, reduced hibernation isn’t necessarily detrimental to bears at a physiological level. After all, many bear species don’t hibernate in the parts of their range where it’s too warm or where food is available year-round.
But, she stressed, if North America’s bears are hibernating less, they have more time to get into trouble. “When bears are awake for more of the year, they’re more susceptible to getting killed,” she told me. “Bears don’t die in hibernation.” In a paper published in the journal Ecosphere, Johnson found that urban areas had become “population sinks and ecological traps” for bears—sucking them out of the backwoods and sending them to an early grave.
Excerpted from Eight Bears: Mythic Past and Imperiled Future by Gloria Dickie. Copyright © 2023 by Gloria Dickie. Used with permission of the publisher, W. W. Norton & Company, Inc. All rights reserved.