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Sunday, September 21, 2014
Colorado bear population much bigger than expected, new study finds
Courtesy Colorado Parks and Wildlife
Putrid, slowly liquifying fish mung. Burlap strips soaked in butterscotch and strawberry extracts.
Colorado Parks and Wildlife researchers used the horribly pungent and the sickly sweet to bait bears in the backcountry north of Summit County this summer.
The two-month study was the latest addition to an ongoing project that wildlife managers hoped would give them a more accurate measure of the state’s bear population and a better gauge of the bears’ behavior.
“One of the big struggles with bears is they’re not particularly easy to count,” said Jerry Apker, Colorado Parks and Wildlife carnivore biologist. When bears aren’t hiding in hibernation, they don’t roam in herds like elk or deer.
So five years ago, the agency started experimenting with a new surveying method called hair snares. Here’s how it works:
The researchers decide on a survey area of around 500 square kilometers, and within that area they set up around 30 hair snag sites. Each one is about 20 square feet, and they surround the site with a string of barbed wire suspended a certain distance from the ground.
In the middle, they hang the bait.
The researchers don’t want their data affected by bears repeatedly coming back for more, so they ensure the bait is hung too high for the bears to reach.
Curious bears follow their noses, and in the process of crawling over or ducking under the barbed wire, they leave behind a few hairs of fur.
Once a week, the researchers check each hair snag site, collect the bears’ DNA samples and then burn off any residue on the wires using a propane torch.
The samples are shipped to a lab in Canada, where they’re analyzed and later used to identify each individual bear. From that genetic information, researchers can tell how many bears live in a particular geographic region and track where the bears move in set time periods.
The results from the closest study to Summit County, completed by biologists working out of Hot Sulphur Springs 30 miles north of Silverthorne, won’t be available until next summer. Analysis from the bear hair snares over the last few years, however, has already shocked wildlife managers.
Researchers found that in every study across the state, in habitats that ranged from good to poor quality for bears, the bear population was double the numbers wildlife managers had been using before.
“I was expecting the numbers to be higher but not twice as high,” Apker said. “We were so surprised and taken aback by the densities that we got.”
The studies have also shown bears using the landscape in a dynamic way, responding to changes in environmental conditions like poor forage quality or drought, faster than expected.
“In the snap of your fingers they’re not in the same areas we thought they would be,” he said.
Not only are the bears moving faster, they’re covering more ground than predicted in response to those habitat factors.
In areas with good-quality habitat, like near the Roaring Fork Valley, bears move around less. They tend to wander through forests following “the green line,” meaning they move up or down in elevation hunting the best vegetation as the seasons change.
During the first hair snag study near Trinidad, researchers found an average of 1.2 bears per square mile. The next summer, that number dropped to 0.5 bears per square mile.
Researchers were stumped by the bear density dropping by more than half until they realized not only had most of the bears moved out of their study area, the females also had synced up reproductively that year.
Colorado’s black bears normally give birth every other year or so when healthy, but after a few years of drought conditions, all the females near Trinidad gave birth to cubs at the same time. Mother bears don’t move around as much, so they had lower chances of encountering a hair snare site.
The next year, all the bears returned.
For decades, Apker said, wildlife managers have relied on old studies that estimated Colorado was home to between 10,000 and 12,000 bears.
“That’s what we hung our hat on for almost 15 years because we didn’t have anything else,” Apker said.
Since then, Parks and Wildlife have tried to estimate bear populations by mapping vegetation and extrapolating from the number of bears killed during hunting season. The hair snag method has improved the agency’s estimates of bear densities in different types of habitat.
“The methodology we’ve got now, it’s better,” he said. “Is it perfect science? No, but we have to use the best we have.”
The technique is more accurate and cheaper, said Kirk Oldham, wildlife biologist in Summit and Grand counties. It’s also much less invasive than old surveying techniques, which usually involved trapping, tranquilizing and tagging the bears.
Oldham said he was surprised his team collected hair samples on 80 percent of the 36 sites set up in his Grand County study.
That could be just a testament to the researchers’ superb bear baiting abilities. It could mean many bears wandering through the sites a few times, or a few bears stumbling through many times.
Whether the DNA analysis shows 30 bears or three, Oldham said, that will play a large role in how the agency manages bears.
He said the agency likes to space bears out according to the size of their home range. Male black bears home ranges can vary between 30 to 250 square miles, while females cover about half that distance.
With public input, Parks and Wildlife soon will put together bear management plans around the state, and the figures from Oldham’s study will inform the bear management strategy for Summit and Grand counties.
Apker said a bear population much greater than expected, combined with an explosion in Colorado’s human population over the last decade, means people living even in cities have good chances of encountering bears.
That means people must learn to tolerate some human-bear conflicts and learn to minimize or reduce the things that cause them, he said. Wildlife managers will be talking with communities about how many bears they want and how to achieve those goals using methods like hunting.
“We do sometimes have to make a decision,” Apker said. “Is this the number of bears that we’re comfortable with?”