Federal Estimate of Yellowstone Grizzly Bear Population is Flawed, Researcher Says

As the U.S. Fish and Wildlife Services considers removing grizzly bears from the list of federally protected animals, a group of researchers is suggesting the method used to report the population of Yellowstone grizzlies is flawed and not an accurate assessment of bruin numbers.

Since the Yellowstone grizzly bear was first listed on the Endangered Species Act in 1973, it has seen a reported population increase from 200 to what's now counted around 700 bears, the Associated Press reports. The upward trajectory has prompted the USFWS to propose once again removing the bears from federally protected status. (Grizzlies were briefly delisted as recently as 2007, but later reinstated as a protected species.)

But new research suggests that from 1983-2010 the USFWS greatly increased their "observer effort," which resulted in increased bear sightings not because there are more bears, but because more bears were seen as a result of looking for more bears. Additionally, a changing dining landscape has forced the bears to search for food in more observable areas, which could also account for more frequent sightings.

"It's a pretty standard thing in all of wildlife biology and conservation biology that if you triple the amount of time you're looking for some rare species, it's likely you're going to seem more of them, just because you spend a lot more time doing so," Daniel Doak, environmental studies professor at University of Colorado and lead study author said, according to the Associated Press.

The study, which was partially funded by the National Defense Council, also asserts that the USFWS grizzly population predictions are overly-optimistic in assuming female grizzly bears reproduce throughout a 30-year lifespan.

The government's latest estimate of 718 bears in the Yellowstone area is up from prior estimates of 600, the AP reported. The 118-bear increase is not the directly observed result of more bears, but a revision to the population estimate based on new calculations.

Doak and his colleagues did not offer an alternative population size or say outright the current estimate was wrong, the AP said, adding that USFWS grizzly bear coordinator Chris Servheen said the governments methods have been reviewed by outside scientists and other government agencies.

"We're certainly interested in what they did," Servheen said of Doak's work. "But we've done a lot of work on this. We've given very careful consideration and critiques to everything we've done multiple times."

But Dave Mattson, a bear researcher with the U.S. Geological Survey, told the AP Doak's study was in line with his own conclusion that the current grizzly population estimations are "essentially worthless."

"There is this belief that somehow, through some sort of statistical magic, you can compensate for bias in your field methods," Mattson said. "My conclusion is that's just not simply possible."