Little bears, big bears, fat bears, skinny bears, young bears, old bears, black bears, grizzly bears, males and females - all seem to greatly enjoy something you and I do everyday: Scratch.

Bears love to scratch. Around these parts, they mostly scratch on trees, but they'll also scratch on fence posts, power poles, road signs and even bridges. All that scratching over the years has provided a treasure trove of DNA information about bears, U.S. Geological Survey scientist Kate Kendall said recently.

Because bears like to scratch so much, they leave hair behind at predictable places - mostly rub trees - along trails used by both bears and people. When a bear leaves hair, it also leaves a little bit of its DNA. For several years, Kendall and a team of technicians, biologists and volunteers have been gathering bear hair - particularly grizzly bear hair - in an effort to learn more about the bear population in Northwest Montana.

The results are both informative and even entertaining. For example, one bear had a penchant for scratching on a bridge. The bear would crawl under the railing and scratch and claw. A remote camera caught the bear in action.

Crews weren't able to take down the camera before winter set it in, but the next April, the camera still worked and the bear was caught on camera again - scratching on the same bridge in 3 feet of snow.

Crews augment these natural scratching trees and posts by nailing barbed wire to them. Crews spend most of the spring, summer and fall gathering hair from hundreds of rub trees across the Northern Continental Divide Ecosystem, a broad swath of land from Glacier National Park south to the Blackfoot River.

The first bear DNA studies in the NCDE in 2004 included bear "traps," where bears were lured into a site using a foul-smelling lure made from rotten cow blood and fish. That study ultimately resulted in the first complete bear population estimate for the NCDE, which at the time was about 765 bears. Today's estimate is about 1,000 grizzlies.

In 2009, Kendall embarked a study using just rub trees and no bait to continue population trend studies in the region. That effort wrapped up last year, and the final DNA results will be available later this summer.

Kendall said it will take a year to crunch the numbers and write a scientific paper on the results, but so far the data indicates annual population growth in the NCDE has been about 4 percent.

Those numbers are similar to another grizzly bear study conducted by Montana Fish, Wildlife and Parks biologist Rick Mace. His study, which involves trapping female bears, radio-collaring them and then studying their reproductive and survival rates, has found the population to be increasing about 3 percent annually.

But Kendall notes the rub tree method has some distinct advantages - for one, it's non-invasive. No bears are handled, and there's no trapping involved. It simply takes advantage of natural bear behavior. Secondly, it doesn't require a biology degree. A trained volunteer can properly gather the hair for analysis.

"I think there's a lot of potential to develop a citizen science approach to this," she said.

DNA testing isn't cheap, however. A complete DNA analysis that determines sex, species and other genetic analysis costs $70 a sample, and Kendall's study includes thousands of samples.

Still, the method has the potential to unlock bear secrets no other study can, such as a bear "family tree" that would trace the lineage of bruins. A post-doctoral student working with Kendall is looking at just that. There's also a host of black bear DNA that has gone largely untouched.

"If we could find funding, we could learn a lot about black bears," Kendall said.

But since grizzlies are still on the Endangered Species List, research has focused on them. Kendall and her team completed a similar DNA study in the Cabinet-Yaak region near Libby this summer. Results from that study are undergoing analysis.

That study has also resulted in some entertaining remote video images of bears caught in the act of scratching. They can be viewed online at http://nrmsc.usgs.gov/research/KendallRemoteCamera.htm.