Entering the bear den: CPW concludes study on human-bear interaction
On a sunny March day, a group of eight crouch silently outside a bear den dug into a ridge near Durango as Colorado Parks and Wildlife’s Heather Johnson literally pokes the sleeping mama bear inside.
This expedition is part of the conclusion of a first-of-its-kind study conducted over six years in southwest Colorado. It is one of the most comprehensive studies to date on human-bear interactions and the impact of urbanization on bear populations.
“This study was motivated by the increase that’s happened in human-bear conflicts in Colorado. As the state wildlife agency that manages those conflicts, we wanted to better understand what was causing those conflicts to increase, and ultimately what we should do about it,” said Johnson, a wildlife researcher.
Some of the questions the study addressed include: Are bear populations increasing or decreasing? Are bear behaviors shifting in response to increased human food sources? How does urbanization influence bear movements, behaviors and population trends?
“We have handled over 600 unique bears in this study,” according to Johnson. Bears were captured within about 10 kilometers around Durango, Colorado. Researchers used GPS collar technology and hair-snare surveys to monitor bear activity and population trends. “A bear’s collar collects their location every hour throughout the day, so we get really good data on the bear’s behavior, where they’re going, what they’re doing, and how they’re responding to different conditions,” Johnson explained.
The group got to this den, the last of about 35 processed over the past few weeks, by climbing a little more than a mile up and over a ridge on the east side of Horse Gulch, about five miles east of Durango. Researchers found the den using telemetry tracking and visually looking for an opening in the ground, which would be easy to miss without the telemetry collar to guide the way.
A tranquilizer needle is attached to the end of the jab pole Johnson pokes into the den, and she gets the adult bear in the perfect spot: the meaty muscle of her shoulder. Johnson and the group speak in whispers while they cover the entrance of the den with backpacks to block excess stimulation. The bear takes about 15 minutes to fall asleep, and then the team removes her two cubs — tucking them safely under jackets to mimic the darkness and warmth of their home — before pulling the 200+ pound bear out of her cozy den. The entrance to the den is barely large enough to pull a full-size bear from. The team removes the bear in order to take body measurements, record her weight, collect a blood sample, and remove the GPS collar. They track her vital rates throughout the process and give her supplemental oxygen to counter any effects from the respiratory depressant they gave her to induce sleep.
“We do our full processing, and then when we’re done we put all the bears back, back in the den just like we found them, all curled up,” Johnson said. “And then we seal up the den again with snow or branches and we hike away. By the time that bear wakes up, we’re gone, it’s quiet, and the bear is sealed back up in the den with her cubs or yearlings. And hopefully she just thinks it was all just a bad dream.”
Since the summer of 2011, researchers have trapped bears and attached collars. Each winter for the following five years, researchers relocated these bears using their satellite collars and entered their dens to count newborn cubs and yearlings. This year, the last year of the survey, the collars were removed. Although she’s no longer wearing a collar to track her movements, the sow and her cubs now have microchips, just like the chips used in household pets.
Johnson, a fearless researcher who also works with other large mammals such as elk and deer, shimmied inside the bear den along with the sleeping bear in order to arrange the bear and her cubs before leaving. “It’s really intimate when you’re climbing into a den, getting into that space and you’re pulling the bears out to do the processing –seeing how many cubs or how many yearlings survived,” she said.
During the six-year project, the researchers worked with residents of the city of Durango to study the effectiveness of urban bear-proofing and how human behavior impacted the local ursine residents. The study deployed 1,100 bear-resistant trash cans into two treatment areas and looked to see whether or not that was effective in reducing bear-human conflicts.
“There was a 50 percent difference between rates of conflict between treatment and control areas,” Johnson said of the bear proofing measures. “If you can reduce access of human food to bears in town and at least 60 percent of your neighborhood is locking away their trash, we see a significant reduction in the number of human-bear conflicts. If you can reduce that forage benefit for bears while the risk of humans and roads stays high, you can tip the balance and keep bears from being willing to forage in town, and then you can reduce conflicts as a result.”
CPW researchers want to ensure the safety of both Colorado’s human and wildlife populations. Studies like this one are crucial to understanding how these groups interact and what factors influence their behavior.
“We are trying to understand if expanding human development is changing bear behavior and then ultimately how to better manage for that,” Johnson said. “Our models project that by 2050, that bears on average will hibernate for about 15 to 40 days less than they do right now. That has big implications for bear-human conflicts because if bears hibernate for several weeks less each year, that’s a lot more time they can interact with people.”
Other organizations collaborating on the study include: the USDA National Wildlife Research Center, an agency within the U.S. Department of Agriculture; Colorado State University; and two private non-profit organizations — the Wildlife Conservation Society and Bear Trust International. Twin Buttes at Durango, a local development company, contributed money toward the purchase of two satellite-GPS collars.
Written by Alicia Cohn. Cohn is a communications specialist for CPW.