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DNA study determines minimum number of grizzlies
Posted: Wednesday, Dec 06, 2006 - 12:17:43 pm MST
By CHRIS PETERSON

Hungry Horse News 545. That's the minimum number of individual grizzly bears in the Northern Continental Divide Ecosystem - a swath of land that covers all of the Glacier National Park, the Bob Marshall Wilderness, the Swans and lands along teh Divide from the Canadian border to nearly Ovando. The overall number really didn't surprise United States Geological Researcher Kate Kendall, who has been doing grizzly bear research since 1977.

“It's about what I expected,” she said.

Of the 545 bears, 46 percent, or 245 unique grizzlies, were inside Glacier National Park, even though the Park amounts to only 13 percent of the study area.

Kendall said the higher number in the Park is likely due to a combination of good habitat and good security. In short, bears in the Park don't run into hunters with guns.

The 545 number comes from a 2004 DNA study of grizzlies and black bears. It is not, Kendall cautions, a population estimate of grizzly bears. That number should come next year when researchers begin crunching numbers from the study through a process known as “mark and recapture.”

In simple terms, mark and recapture creates a population estimate based on the number of bears that are caught in each trapping session.

DNA traps don't actually catch the bears. The bear is attracted to a scent pile, and when it walks to the pile to sniff around, it leaves some hair on a barbed wire fence around the pile.

The trap is left out for two weeks, then removed and placed in other location, covering the landscape in 7-by-7 kilometer grids throughout the ecosystem for eight weeks.

As the trap is moved, some bears that visited it the first time are caught again. While other new bears find the trap as well. This is known as mark and recapture.

For example, if 10 bears visited the trap the first time, and five of the same bears visited the same trap a second time, you would have a 50 percent recapture rate.

Extrapolate that out over time and with a network of traps through the ecosystem and researchers can determine not only how many bears they caught, they can also get a very good handle on how many bears they didn't catch.

From that, comes a population estimate.

It took a small army of biologists and volunteers to pull this all off. All told it cost about $2.1 million in 2004 and took about 210 people.

Then all the DNA had to be analyzed. While the study also caught plenty of black bear hair, that DNA hasn't been analyzed, Kendall noted. There isn't enough funding for it right now, but she said she's working on it.

In general terms, however, black bears outnumber grizzlies, especially outside Glacier National Park.

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