Colorado study: Findings expected to change human efforts to control bears
DURANGO, Colo. — Curled up in a den on an acorn-rich hillside, a hibernating bear and her three fuzzy cubs face increasingly perilous conditions.
People in homes 200 yards below constantly tempt them with food — this 180-pound sow knows well how to navigate garbage-scented urban smorgasbords in late summer if acorns and berries vanish. But state policy requires extermination of bears repeatedly caught eating garbage. Record numbers are dying. And the dozing bears also feel warmer temperatures near their rocky den that shorten hibernation.
Now, near the top of the hill, a Colorado Parks and Wildlife research team with a tranquilizer dart on a 6-foot jab pole is creeping toward them.
This den visit is one of the last in a six-year study of black bears in Colorado that challenges core assumptions state wildlife managers have relied on for decades. Rising conflicts with people motivated the CPW study, which will be published this year. Seldom have scientists tracked and monitored so many bears so closely, even analyzing fur to verify what bears ate.
The findings are expected to change human efforts to control bears.
- CPW researchers concluded that increasing bear-human conflicts do not mean the bear population is growing but that bears are adapting to take advantage of urban expansion. This will compel a rethinking of Colorado’s current approach of boosting bear hunting based on the number of conflicts reported in an area. If bears aren’t multiplying, heavy hunting could hurt the species.
- The researchers also found that bears who eat garbage do not become addicted. This clashes with the current belief that has justified a two-strikes policy of euthanizing “food-conditioned” bears. CPW’s team determined that bears use human food when necessary — to boost their weight so they can reproduce — but switch back to natural berries and acorns when possible.
- CPW tracking established that rising temperatures around dens and urban development in bear habitat significantly shorten hibernation — which means more time for bears to clash with people.
- And Colorado’s bear population could decline if current trends and practices continue. In southwestern Colorado around Durango, where researchers studied 617 bears starting in 2011, the female bear population has decreased by 60 percent.
“We could see a ratcheting down of the bear population,” said CPW biologist Heather Johnson, leader of the research, who used radio collars and monitored movements of 40 bears at a time.
“Human development is really expanding,” she said. “There’s shrinking safe space for these wild bears to be.”
Colorado officials quickly could end their policy of euthanizing bears in response to the findings, Colorado State University conservation biologist Barry Noon said. However, he said, “the key driver of bear populations is going to be the carrying capacity of the environment. And that is going to be related to soil moisture and plant productivity — which is directly related to the climate. You cannot change policy overnight on accumulation of carbon dioxide in the atmosphere, rising temperatures and changes in precipitation. We will want to be addressing these ultimate factors that are driving wildlife populations.”
Crew members know B268 as a bear who stays more or less wild, a 5-year-old who gorges on chokecherries, serviceberries and acorns despite living within sight of loaded, green, 50-gallon trash cans sitting near homes at the edge of Durango, a city in far southwestern Colorado with a population of around 20,000.
“She is surrounded. She’s got this one ridgeline. There’s houses all around, and she’s behaving for the most part the way we want a bear to behave,” Johnson says. “She has hopscotched around this landscape trying to be a natural bear as best as she can.”
They also know B268 has not been moving since November.
Crouching in snow and ice on the hillside 50 yards from her den, CPW crew members speak in low voices, saying they expect to see perhaps two cubs. Heading into hibernation, B268 weighed 220 pounds, relatively robust. Crew members whisper that they expect B268 will be, like most bears in the study, an easy, groggy target for their tranquilizer dart.
She might growl a bit, then slump into a deep torpor at the back of her cave with any cubs, the researchers say. They easily could take measurements, inject ID chips at the backs of any cubs’ necks and slip off B268’s collar to get data it held showing her precise locations every hour this past year.
But, as the crew scrambles, rustling through dry oaks and peeking into the den, B268 catches wind. She stirs, as if from a bad dream. Johnson and fellow CPW biologist David Lewis see she had given birth to three cubs, now crawling against her furry belly, hungry for more of her milk.
Johnson and Lewis are further surprised to see B268’s den has two openings. So much for the easy entrapment. Lewis realizes he has only seconds. He dives forward with the pole. He pushes the tranquilizer into B268’s left shoulder.
She awakens. Lewis and Johnson stand steady at the front of the den. B268 bolts out the back. She climbs on top of the rocks over the den where, bristling in the sunlight against the blue sky, she jerks her head right and left, looking around. Then B268 bounds away, nearly toppling CPW technician Emily Gelzer.
“Bear!” she shouts.
B268 runs uphill, claws churning snow and ice, toward cliffs. She runs about 100 yards, leaving her cubs behind in the den, writhing in still-warm dirt.
The researchers watch, worrying they’ll lose B268.
Meanwhile, the cubs, about 7 weeks old, begin shivering.
Johnson improvises, lifting the cubs out of the den and having crew members and observers hold them inside their down coats as she and Lewis look for B268. The cubs squirm and growl, tumbling over one another, squinting in the sunlight, batting the air with tiny claws.
For decades, Colorado wildlife managers have been trying to control bears, aiming for peaceful coexistence with people.
But they’ve lacked — and still lack — key information: the overall number of bears statewide. Now as Colorado’s 5.54 million human population expands toward a projected 10 million, rising bear-human conflicts present practical and ethical conundrums. The number of bear-human conflicts, more than 1,200 in 2015, is growing more than twice as fast as the human population by about 4 percent a year.
There’s evidence suggesting that bears, like other large carnivores once common in the West, could be aced out in the future.
Two decades ago, before Colorado’s population boom, state wildlife managers counted about 600 bear deaths a year, according to data reviewed by The Denver Post. The number of bear deaths surged to more than 2,000 in 2014. Vehicles kill increasing numbers of bears. Scared cubs sometimes mistake power poles for trees and are electrocuted as they scramble from danger.
“For our agency, it is a huge issue. It is only going to get worse — a lot worse,” Johnson said. “If bears are denning less, they’re active longer. They’re interacting with people more. It’s going to change the numbers of interactions people have with bears. We should expect our rate of interactions with bears to really increase.”
CPW officials say they lack info because counting bears, often elusive in remote areas, can be costly. No statewide population survey has been done. CPW leaders have estimated 17,000 bears, based on collection of hair-snag samples and extrapolations. They’ve said the estimate isn’t reliable, that bear-counting methods have changed and that, with no consistent counting, state wildlife managers don’t really know whether the bear population is increasing or decreasing.
Yet Colorado officials have allowed increased hunting, issuing 17,000 bear-hunting licenses in 2014, up from 10,000 in 1997.
The CPW researchers determined that, at least in southwestern Colorado, bear-human conflicts cannot be taken as proof of a growing bear population. Johnson said computer plots show conflicts happen because bears wander into cities looking for food when natural foods aren’t available during dry years, which with climate change is expected to happen more often.
Bears are changing their behavior, shifting to forage inside cities when necessary, then shifting back to natural food when that is available, Johnson said. Monitoring data show 80 percent of bears entered Durango during dry summers and feasted without becoming addicted. About 15 percent continued to forage regularly but not exclusively in Durango. Bears can smell food from more than a mile away. Johnson said they have long memories and quickly adapt to obtain food without getting caught.
“They recognize risks of foraging in cities, but also benefits,” she said.
During the study, CPW officials worked with Durango officials to put bear-proof trash cans at homes in some neighborhoods. They found that this reduced bear-human conflicts. In areas without bear-proof cans, conflicts increased sharply.
“This research will go a long way towards taking the guessing game out of how to better manage black bears and reduce conflict,” said U.S. Department of Agriculture researcher Stewart Breck, who has focused on carnivore ecology and behavior. “The question is whether or not people will listen.”
Beyond foraging, CPW researchers focused on hibernation. They determined that bears hibernate seven days less for every 1.8-degree temperature increase at their dens. In addition, for every 10 percent increase in overlap of foraging terrain with urban development, hibernation decreased by three days.
“As the average temperatures in this state increase,” Johnson said, “we should expect our bears will sleep less.”
That means bears probably will be more active, leading to more potential encounters with people.
The end result? Bears lost out, because even though human food helped them reproduce, fewer were able to survive. From 2011 to 2016, CPW researchers documented a drop in the female bear population to 84 from 200, mostly due to a dry year in 2012 that drove more bears into Durango. The population didn’t bounce back.
As the tranquilizer takes effect, B268 collapses and tumbles down through snow. Johnson and Lewis scoot her onto a tarp. They put an orange cap over her eyes for protection. They take her pulse and haul her back to a ledge by the den.
They insert oxygen tubes in her nose, feeding her air as a precaution as they work over her body. They snip off fur for testing and remove the radio collar. Three months hibernating and the birth of her cubs dropped her weight to 180 pounds.
Over the past year, B268 survived mostly by crisscrossing the hillside above the city, but she also popped into neighborhoods and the city’s water supply reservoir now and then. Tracking data show she avoided businesses, schools and government offices.
The cubs (B599, B600, B601), from this birthplace, likely will hang with their mother until 2018. Sows push cubs away as 2-year-olds when boars swing back for more breeding. The cubs — two males and a female — will wander up to 50 miles seeking sufficient berries and acorns, unless they become habitual city bears. A young bear must fight off older bears in establishing foraging areas.
“Their mortality risk will be a lot lower in the wild than in town,” Johnson said.
The cubs have a 50 percent chance of surviving one year.
The CPW team hoists B268 back into her den, laying her on her right side the way she was when they interrupted her hibernation. Johnson strokes her fur and lifts her leg. And she tucks B599, B600 and B601 against B268’s belly.
Feeling the rising and falling of her breathing, the cubs settle, closing their eyes. B268 licks them and her eyes open slightly as the tranquilizer begins to wear off.
And now in the den, protected above the city, they’ll be about as safe as bears can be into spring, Johnson says. “It’s definitely a lot safer than them being out there in the world.”