The Yellowstone Ecosystem grizzly bear population fell by 10 bears from 2019 to 2020 and now numbers 727, according to new estimates from an interagency team of scientists.
The figure accounts for the grizzly bear population in the 19,270-square-mile demographic monitoring area in and around Yellowstone National Park. Bears in that area are monitored under the auspices of the Endangered Species Act.
The decline — about 1.4% — is no reason to worry about the population’s size, a top team biologist wrote.
“There is no biological significance to a 10-bear difference in the estimate from one year to the next (up or down), considering the inherent variation in these estimates,” Frank van Manen, supervisory research wildlife biologist with U.S. Geological Survey’s Interagency Grizzly Bear Study Team, wrote in an email.
The estimate meets the 500-bear goal necessary to qualify as a recovered population under the Endangered Species Act, although managers seek a buffer above the figure. Grizzlies remain listed as a threatened species while the U.S. Fish and Wildlife Service resolves court-specified deficiencies in plans to remove federal protections.
The 2020 summary (see below) is a factual report, van Manen wrote, not a policy document that determines whether numbers meet ESA population recovery goals. “Given the science role of IGBST, we provide the demographic findings for managers to determine whether demographic monitoring criteria are met,” he wrote.
The IGBST releases the full annual report later in the year.
At the hand of man…
In the last five years annual population estimates have ranged between 695 in 2016 to a high of 737 in 2019. Thirty grizzly bears were known to have died or probably died in the DMA last year, the summary states.
Twenty-eight of those died due to human causes, according to the 2020 summary. That means human-caused mortalities account for 93% of the known and probable deaths.
Human-caused mortalities included bears captured and euthanized after killing livestock or frequenting developed areas after becoming habituated to human food, or after being struck by vehicles. Several deaths remain under investigation, a category encompassing grizzlies killed by hunters or others claiming self-defense.
Thirteen of the human-caused mortalities were “management removals” — mostly involving high-conflict, dangerous or unfit bears euthanized after run-ins with people or their property.
The summary provides other clues to the health of the population, including the sightings of females with cubs in the ecosystem’s core. The center of the ecosystem — an area covering 48% of the DMA — is subdivided into 18 bear management units where grizzly mothers are highly valued.
Observers documented females with young in all 18 of the units in 2020, a figure that’s held constant for three years running.
The summary also pegged estimated mortality for independent females in the DMA at 7.5%. That figure that will be considered along with previous years’ information before managers determine whether recovery goals involving that metric have been met.
Another reason the 10-bear difference is insignificant is the “conservative nature of the Chao2 estimation technique,” that was used to arrive at the figure, he wrote.
The Chao2 model gave scientists a high degree of confidence there are between 648 and 806 bears in the DMA, according to the team’s summary of monitoring in 2020.
Scientists also compiled information on several grizzly food sources and determined that a key one — whitebark pine nuts — appears to be holding up. Beetle infestations threatened the species abundance in the ecosystem.
The number of whitebark pine cones found along delineated survey routes remained “similar to the long-term average,” the summary states. “These data suggest the mountain beetle outbreak has run its course,” the paper reads.
Certainly, many Yellowstone grizzlies live unseen lives, rarely observed or counted by humans even after their demise. Nevertheless, the monitoring program includes exhaustive detail gathered from ground observations, flights to spot bears hunting army cutworm moths in talus fields, surveys of spawning trout and other data-gathering.
Grizzly skulls and other remains found years after a bear’s demise are eventually incorporated into the database.
Wyoming conflict captures decline
Last year wildlife managers also recorded 19 grizzly deaths outside the DMA, where the population is irrelevant to federal recovery goals. Wyoming Game and Fish Department tracks statewide grizzly activity, reporting 26 captures in Wyoming in 2020, down from 33 in 2019.
Eighteen of the bears caught for conflicts in Wyoming were removed in coordination with the U.S. Fish and Wildlife Service. That’s the same number taken out in 2019 and includes bears inside and outside the DMA.
Some bears trapped for conflicts get another chance. Game and Fish last year relocated nine bears it trapped, down from 15 in 2019.
The availability of natural foods has the biggest influence on the ebb and flow of capture and removal numbers, said Brian DeBolt, Wyoming Game and Fish Department’s large carnivore conflict coordinator. The recent high tide of grizzly removals in 2018 illustrates that point, he said.
“It was just the result of poor natural foods,” he said. “We had a lot more bears encountering a lot more people.”
Grizzlies were “aggressive in the backcountry,” in 2018 he said, another indication of that poor food year. A grizzly killed a hunting guide in the Teton Wilderness that year.
Game and Fish dealt with more than 200 conflicts in 2020, DeBolt said. The agency resolved most of those without having to capture a bear.
In about 80% of cases, “we were able to resolve that conflict in some other way,” he said. “We were able to erect an electric fence … or remove the attractant.”
Removals of grizzlies protected by the Endangered Species Act “are not taken lightly” he said. Those decisions rest with the U.S. Fish and Wildlife Service, which largely relies on Game and Fish field personnel for trapping, relocation and information. “We try to target those individual bears that chronically cause problems,” DeBolt said.