Yellowstone grizzly cubs stand up to take a peek above the sagebrush. To calculate population estimates and trends, scientists seek information on the number of bears in and the composition of the ecosystem population. (Jim Peaco/National Park Service)

An effort to refine Yellowstone-area grizzly bear population estimates is disturbing conservationists who fear it could lead to increased hunting and other bear deaths.

A federal scientist told Yellowstone area grizzly managers this spring he is developing a method to more accurately count grizzly bears and hopes to present his “integrated population model” to them next year. Members of the Yellowstone Grizzly Coordinating Committee could then consider whether to use it instead of the existing formula, called Chao 2, which some have argued underestimates bear numbers by up to 50 percent.

The new census method is being crafted despite an agreement among federal and state officials to use Chao 2 into the “foreseeable future.”

The federal government transferred grizzly management to states in 2017 following years of negotiation and eventual agreement on population objectives, among other things. Changing population estimation methods could increase the official count, which critics fear would make more grizzlies available for hunting or other “discretionary mortality”.

The announcement comes at a time when the National Parks Conservation Association is worried about what it calls an aggressive Wyoming plan to let hunters kill as many as 22 bears this fall, Stephanie Adams, the group’s Yellowstone program manager told officials in April. Idaho hunters could kill one more. If officials decide there are many more grizzlies, perhaps hundreds more, conservationists fear hunting quotas could increase dramatically in coming years.

Science, not policy

United States Geological Survey scientist Frank van Manen, a member of the Interagency Grizzly Bear Study Team, told Yellowstone managers in April he is working on the new method. He told WyoFile the desire for greater accuracy has been present for decades.

“It’s poor policy not to progress with science,” he said. “How the policy makers — the managers, the agencies that sit around the table — how and if they incorporate any new information in the future is really their prerogative.

“My task is to supply the most reliable science to the committee,” he said. “We do not make recommendations to managers.  We don’t set or influence policy that way.”

Grizzly bear advocates have worried for some time that policy makers might change the counting method and in doing so undermine existing safeguards for the bears. At issue is an agreement among state governments forged when the U.S. Fish and Wildlife Service decided there were enough Yellowstone-ecosystem grizzlies and protected habitat to remove the species from the list of threatened species and turn management over to the states.

Ninety-nine percent of visitors to Yellowstone National Park, like these near Canyon, hope to see a grizzly or black bear and 63 percent actually see one according to a park study. Bear viewing creates 155 jobs and generates $10 million a year, the study says. (Jim Peaco/National Park Service)

The agreement among Wyoming, Idaho and Montana requires that the states will maintain at least 500 grizzlies in the ecosystem’s 19,270 square-mile demographic monitoring area. If there are fewer bears, federal protection could be re-imposed and hunting and other “management removals” stopped. To ensure consistent counting methods, and thus the integrity of the deal, conservationists, including Yellowstone superintendent Dan Wenk, secured assurances that the Chao 2 method would be used for the “foreseeable future.”

Wenk’s concern is that the framework contains enough ambiguity for a counting change to radically reduce bear numbers and damage bear watching in Yellowstone. Ninety-nine percent of Yellowstone visitors hope to see a bear — grizzly or black — and 67 percent do see one, according to a park study.

Visitors would spend at least $41 more for a guaranteed grizzly sighting, a park survey revealed. The grizzly-watching industry creates 155 jobs and generates more than $10 million a year, the study said.

“My fear is if they use another method of counting … they’ll implement higher rates of mortality to drive the population down,” Wenk told WyoFile in 2016.

Bear bait and switch?

Conservationists see potential liabilities in the agreed-to plan for states to manage grizzlies. That conservation strategy refers six times to “best available science.” The strategy also states that the Interagency Grizzly Bear Study Team, which reviews the bear’s status regularly, “may continue to investigate new methods for population estimation as appropriate.” But, the strategy adds, “the model-averaged Chao2 method will continue to be used for the foreseeable future.”

Continuing to use a consistent method of estimating population would ensure that managers are comparing apples to apples, Wenk told WyoFile in 2016. But changing methods could indicate there are 300 or 400 bears more than agreed-to objectives. That could put something like 400 bears at risk, Wenk has said, potentially altering the entire ecosystem.

In part because of that concern, Wenk was the only member of a Yellowstone Ecosystem  Subcommittee who voted in 2016 against plans to remove federal protection of the bear.

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His resistance put the federal government in the awkward position of proposing to remove federal Endangered Species Act protection from the Yellowstone grizzly bear while a principal grizzly manager – the park superintendent — opposed delisting.

Wenk’s resistance prompted a series of letters — recently obtained by WyoFile and published below — among high-ranking state and federal officials seeking clarifications and reassurances that delisting would be allowed to advance. On Dec. 14, 2016, Dan Ashe, then the director of the U.S. Fish and Wildlife Service overseeing grizzlies, wrote Wenk’s National Park Service boss to placate delisting criticism.

Chao 2, Ashe wrote, would be used “as far into the future as we can reliably envision.” He made the assurance based on “extensive conversations with the states,” he wrote. Changing to another counting method is “not a foreseeable event,” Ash wrote.

Yellowstone visitors prepare themselves for an encounter with a bear. (Jim Peaco/National Park Service)

Wyoming Gov. Matt Mead joined the discussion in a Dec. 16, 2016, letter to then-Secretary of the Interior Sally Jewell, who oversaw the National Park Service at the time. In it he said Wyoming agreed to manage grizzly bear populations according to a tristate agreement forged to enable delisting and state management. That tristate agreement states that Wyoming, Idaho and Montana will use the Chao 2 estimator in determining the population.

Wyoming has repeatedly stated it would manage grizzly numbers beyond requirements of the Endangered Species Act and would ensure the Yellowstone population persists. Among its pledges are to not allow hunting in the John D. Rockefeller National Parkway between Yellowstone and Grand Teton national parks and to institute a no-hunting buffer east of Grand Teton to protect popular roadside grizzlies there.

The Wyoming agreement with Idaho and Montana calls for an ecosystem population of 674 bears. There were 718 grizzlies in the population in 2017, according to estimates using Chao 2, the method named after Taiwanese environmental statistician Anne Chao.

Only after receiving Mead’s letter did Wenk, along with his Park Service bosses, “express our support for that [conservation] strategy and for the delisting proposal.” Secretary of the Interior Ryan Zinke removed the grizzly bear from the list of threatened species on June 22, 2017. That enabled Wyoming to approve the first grizzly hunt since 1974. Conservation groups have sued, challenging the delisting.

“This achievement stands as one of America’s great conservation successes; the culmination of decades of hard work and dedication on the part of the state, tribal, federal and private partners,” Zinke said upon delisting. A department press statement added that multiple factors indicate the population is healthy “and will be sustained into the future.” These include “the states’ commitments to manage the population from now on in a manner that maintains its healthy and secure status.”

Are Wenk’s fears realized?

At the April Yellowstone Grizzly Coordinating Committee meeting in Cody, Wenk saw his fears partially realized only 16 months after expressing them to WyoFile, and receiving assurances to the contrary from state and federal officials. “One of the things that was talked about when we were going through this process is a commitment to the Chao 2 for the foreseeable future,” he told the committee, according to minutes posted online. “We support best available science. I just think we have to be aware of the cascading implications that has within the conservation strategy – population numbers, mortalities, etc…”

Van Manen’s model — described as an integrated population model — is being crafted in collaboration with researchers in three ecosystems and would reconcile possible biases in population estimates, survival estimates and mortality estimates. The scientist said he has no idea whether the new model will lead to a higher estimate for grizzly bears or even whether “it actually improves the current system.

Although states now manage bears, the committee of federal and state land and wildlife managers “will guide how the ecosystem population will be managed,” the committee states on its website.

“There’s no suggestion from us that something would change,” van Manen said. “We simply report scientific findings and facts to the committee. It’s entirely up to the committee to incorporate that into their policies.”

Secretary of the Interior Ryan Zinke, right, greets Cameron “Cam” Sholly, who was recently named to be the new superintendent of Yellowstone National Park. He will replace Dan Wenk, the only Yellowstone Ecosystem Subcommittee member to vote against removing Endangered Species Act protections guarding the Yellowstone grizzly bear. (Department of the Interior)

Although scheduled to be revealed next spring, van Manen cautioned against expecting a new counting system soon.

“Things don’t move so fast on our end,” he said. “The science, even though the project might be finished next year, it would still require some pretty elaborate evaluation…. If anything we’re a couple years out [from] knowing what that estimator would look like and how we would implement that.”

Policy makers, “they have to indeed be careful not be comparing apples to oranges,” he said. One cannot base minimum population requirements on one model and allowable mortalities on another, he said. “You have to work off the same estimator.”

Zinke has greeted a new Yellowstone superintendent named to replace Wenk, who leaves unfinished business and remains skeptical about the bear’s future. At his last committee meeting in Cody he told fellow managers, “I guess we now have a definition of ‘foreseeable future.’”

Angus M. Thuermer Jr. is the natural resources reporter for WyoFile. He is a veteran Wyoming reporter and editor with more than 35 years experience in Wyoming. Contact him at or (307)...

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  1. Great article Angus.

    One of the most important factors in a population estimate is trend, so it’s possible to know if the population is increasing or decreasing. If there’s not a significant overlap of counting methods it would be impossible to know if, or how much, the population is decreasing with hunting. That may not be the motive for scientists to switch methods, but it’s a safe bet that’s why the political types are considering it..

    I’m assuming the proposed new methodology is a mark/recapture technique where a certain number of animals are marked in order to compare the ratio of marked and non-marked animals. For this method to work a significant number of animals would need to marked in a highly visible manner which is expensive and always a risk to the bears.

    The Chao 2 method simply uses the cubs of the year as the “marked” animals which is a far less invasive method and it has the advantage of keeping very close tabs on reproduction, which is valuable information.

    If they do switch counting methods, it seems that an overlap of several decades would be the only responsible way to do it.