Greater Yellowstone Ecosystem grizzly distribution

Federal scientists estimate that there are 1,069 grizzly bears occupying the “demographic monitoring area,” illustrated in this Greater Yellowstone Ecosystem map. An unknown additional number of bears dwell within the occupied range beyond that zone.

Biologists tasked with monitoring grizzly bears in the Greater Yellowstone Ecosystem have a new official population estimate, and because of a methodology change there are — at least on paper — significantly more bears.

U.S. Geological Survey ecologist Frank van Manen, who leads the Interagency Grizzly Bear Study Team, reviewed the updated numbers Monday while giving a presentation to the Interagency Grizzly Bear Committee’s Yellowstone Ecosystem Subcommittee. Using a model known as “Chao2” to estimate population, federal biologists predict there are about 371 independent male grizzlies 2 years or older and a similar number of independent female grizzlies. An additional 326 grizzly cubs plus yearlings are believed to exist.

“That adds up to [about] 1,069 bears, total population size for the Greater Yellowstone Ecosystem,” van Manen said. “That’s a higher number, of course, than we reported last year. That’s strictly due to the change in methods of the Chao2.”

A year ago, the estimated population in the “demographic monitoring area,” where grizzlies are counted, penciled out to 727 animals.

Meeting with the Yellowstone subcommittee last spring, van Manen signaled that a revision to a key criterion underlying the count was in the works, the effect being a 34% to 43% jump in the population estimate.

While the Chao2 method remains in place for now, what changed is a filter determining how many female grizzlies with cubs get plugged into that model. Historically, sows and cubs spotted from the air within 19 miles of each other were only tallied once to avoid double-counting bears. But an analysis found that this buffer was too broad. Now, only sows with cubs detected within 10 miles of each other are excluded to avoid duplication.

Based on several other metrics, van Manen suggested that the Yellowstone region’s grizzlies are thriving.

Having well over 300 cubs and yearlings indicates “really solid” reproduction in the population, he said. Females with cubs were well distributed, documented in all 18 “bear management units” spread within the inner “recovery zone.” Lastly, grizzlies continue to occupy more habitat farther from the ecosystem’s core in Yellowstone National Park and the adjoining necklace of protected wilderness.

As of the end of 2020, grizzly bears’ occupied range encompassed more than 27,200 square miles. More than 40% of that habitat falls outside of the demographic monitoring area where grizzlies are currently counted. Although grizzly densities on the fringes of occupied range are likely less than within the ecosystem’s core, scores of grizzlies — potentially several hundred — are not being factored into the 1,069 population estimate.

Grizzlies were protected under the Endangered Species Act in 1975, an era when the population was largely confined to Yellowstone National Park and there were as few as 136 bears remaining. Ursus arctos horribilis’ range has slowly stretched ever since. Numbers have surpassed recovery goals for many years, and twice since 2009 the U.S. Fish and Wildlife Service and the states of Idaho, Montana and Wyoming have sought to revoke federal protections and manage grizzly bears themselves. Both times federal judges overturned the decisions.

Political pressure is mounting for a third attempt at “delisting” the apex species, although Fish and Wildlife’s “five-year status review” of grizzlies across their range in the Lower 48 did not recommend making changes to the Yellowstone subpopulation when the document was completed this past spring.

The state of Wyoming is planning to force the issue.

In September, Wyoming Game and Fish Department Director Brian Nesvik and Wyoming Gov. Mark Gordon announced they’d soon be petitioning the Fish and Wildlife Service in pursuit of the state’s desire to manage and hunt its population of grizzlies unencumbered by the Endangered Species Act.

Contact Mike Koshmrl at 732-7067 or env@jhnewsandguide.com.

Mike has reported on the Greater Yellowstone Ecosystem's wildlife, wildlands and the agencies that manage them since 2012. A native Minnesotan, he arrived in the West to study environmental journalism at the University of Colorado.

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