There's No Evidence ‘Threatened’--But Growing--Grizzly Population ‘Was Ever Severely Reduced’
September 20, 2008 - 11:03 PMA federal study of Montana grizzly bears based on a massive collection of DNA samples has produced "no evidence" that the grizzly population in that region of the country--which has been listed as threatened since 1975--"was ever severely reduced."
“Overall, the genetic health of the population is good,” U.S. Geological Survey Scientist Kate Kendall, the lead researcher on the project stated last week.
“With diversity in the population approaching levels seen in undisturbed populations in Canada and Alaska, there is no evidence that population size was ever severely reduced or that its connection to Canadian populations was broken,” she said, in a news release put out by U.S.G.S. “The genetic structure suggests that there has been population growth between 1976 and 2007.”
The five-year study monitored the grizzly bear population in a 7.8 million-acre area in northwestern Montana.
In a recorded internal agency interview posted by the U.S.G.S., Kendall said that this was the first ever ecosystem-wide assessment of this particular grizzly population—even though the government has listed it as threatened for more than 30 years.
“It’s important because there are only 5 grizzly bear populations remaining south of Canada, and although this population has been listed as threatened since 1975, there was no ecosystem-wide information about how the population was doing,” she said.
To conduct the survey, scientists set up “hair traps” for bears, which consisted of a hundred feet of barbed wire wrapped around several trees. Within this “corral” of barbed wire, the scientists put a “scent lure” to draw bears in. When a bear approached, it usually snagged hair on the wire. Scientists later collected this hair and checked its DNA to establish the bear’s identity.
The scientists also collected bear hair from naturally occurring bear-rub trees.
In all, the scientists collected 21,000 samples from hair traps and another 13,000 from bear-rub trees.
When genetic analysis was done on the DNA from these hair samples, it was determined that they came from 563 different grizzlies. Using a statistical model based on past records of bear sightings and past samples of bear DNA, researchers were able to account for bears that did not enter one of their hair traps or use one of the bear rub trees included in the study to estimate a total grizzly population of 765 in the area studied.
“From the individual bears that were identified from the hair samples, we estimated that in our 7.8 million acre study area the population had 765 grizzlies,” Kendall said in the interview posted by U.S.G.S. “Then by plotting the location of all records of bear sightings and DNA detections from 1994 to 2007, we found that grizzly bears had expanded their range by 2.5 million acres outside of the area thought to be occupied in 1973.”
By leaving behind automatically triggered video cameras, the researchers were also able to collect unique video footage of grizzly bears cavorting at bear rub trees.
“One we call the dancing bear that just gets this kind of rhythm going,” Kendall said in the taped interview released by U.S.G.S. “He’s rubbing on the tree, and then kind of shimmies on down to a squat and then back up again.”
“Then there is this other one,” she said. “He sort of does this hand jive thing when he’s rubbing. It’s just very amusing.”