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Natural Resources & Energy

New calculation method results in the largest grizzly bear population

Grizzly bear sow and cubs
(NPS Photo/ Tim Rains)
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The Greater Yellowstone Ecosystem grizzly bear population is the largest it has ever been. It's estimated that almost 1,070 grizzly bears are in northwest Wyoming and parts of Montana and Idaho. That number is much higher than the previous estimates which put the grizzly's population estimate at around 750 bears.

Frank van Manen, the team leader of the Interagency Grizzly Bear Study Team which calculates the population, said they are using a less conservative method to count the bears.

"It was a recovering population that you didn't want to overestimate," he said. "And so by design, it ended up underestimating the population. And that was shown in a publication from the study team back in 2008."

The Interagency Grizzly Bear Study team uses a system that plugs several data points into a model to calculate a population number.

One data point is how many female grizzlies with cubs have been spotted that year. Van Manen said that number is often conservative, partly due to the distance criteria of 30 kilometers between bear families.

"Say it's 70 females with cubs on the ground. We can only identify maybe 50 of those simply because that criterion was too conservative to separate observations out into the unique clusters of individuals that they actually belong to," he said.

Van Manen said they decreased the distance to16 kilometers for a better estimate. This is the first year they are using the new approach, but it appears to be more accurate of the actual situation on the ground.

"Because the population estimate is higher and we look at mortality, the percentage of mortality of the population is actually more in line with some independent methods of estimating survival rates, for example," he said. "So, that actually puts extra credence into these new values."

Van Manen said the management of the grizzlies will remain the same.

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