Yellowstone bison population estimated at 4,800

BILLINGS – A healthy calf crop helped Yellowstone National Park’s bison rebound somewhat from one of the deadliest winters in the animals’ recent history, according to a park status report.

An estimated 1,551 bison were killed in 2022-23, equal to about 27% of the 2022 summer population of about 6,000 animals. This summer’s population was estimated in August at about 4,800 animals, according to Chris Geremia, bison program manager.

As a result, the Park Service is recommending no more than 1,100 animals be removed from the population this season to ensure the herd size remains above 3,500, a population target meant to maintain the animals’ genetic diversity.

Meeting

The recommendations came as members of the Interagency Bison Management Plan (IBMP) met at Chico Hot Springs Resort on Oct. 31. The Montana Department of Livestock is the host of the meeting, which rotates among the partners.

The gathering follows Montana IBMP partners’ written criticism of the Park Service’s proposed bison management plan, released this summer.

Gov. Greg Gianforte and the leaders of Montana Fish, Wildlife & Parks and the Department of Livestock signed a letter, which in part said the National Park Service didn’t cooperate during the planning process. The leaders called the park’s staff “uncollaborative and obstinate” and referred to Yellowstone’s analysis as “deficient and misstated.”

The state leaders also emphasized Montana “has always managed and participated as an IBMP partner with a bison population of 3,000 as the goal,” not the park’s stated minimum of 3,500.

In the end, the state executives asked the Park Service to reconsider its management proposals or litigation is inevitable.

Tolerance

The 17-page letter includes a not-so-veiled threat that should the Park Service proceed with its proposed bison management plan as written, the state might revisit the 2015 decision by then-Gov. Steve Bullock to expand the so-called tolerance zone for bison to the west and north of Yellowstone into Montana.

The state leaders called “unreasonable” the park’s assumption in writing the bison management plan that tolerance zones would persist.

In the aftermath of the state’s letter, conservation groups supporting bison and the park are preparing for a fight.

In a news release, the Greater Yellowstone Coalition’s executive director, Scott Christensen, wrote: “It’s clear the vast majority of Montanans and citizens of this country support a balanced, modern approach to conserving Yellowstone’s iconic bison, and so do we. Over the past nearly quarter century, there have been significant changes in the Gardiner and Hebgen basins that have opened more critical winter habitat for bison, new management tools developed like the Bison Conservation Transfer program, and major advances in science. We commend Yellowstone National Park for recognizing the need to update its approach to bison management in ways that reflect current conditions.”

Recommendations

In its proposal to IBMP partners, the Park Service advised the number of bison killed or captured this coming winter should depend on the magnitude of the migration. The agency also called for restricting bison removals to the north of Yellowstone. In culling the herd, no more than 20% should be calves with more females taken (57% to 70%) than males.

If enough animals migrate out of the park, some could be trapped and tested, with brucellosis-exposed bison shipped to slaughter. Brucellosis exposure is endemic in Yellowstone. If spread to livestock, the disease can cause pregnant cattle to abort. Fear of bison infecting cattle with brucellosis is Montana’s main reason for restricting the animals’ movements outside the park.

Elk also carry brucellosis, but are not similarly confined. Instead, the state works to keep cattle and elk separated, especially in the spring when it is believed the disease is more likely to be transmitted by infected birthing material.

Record hunt

This past winter, extended cold and deep snow drove Yellowstone bison north into the Gardiner Basin, resulting in the largest tribal hunting success on record – at least 1,010 bison were shot. Another 282 were placed in the Bison Conservation Transfer Program, which moves live, disease-free bison to tribes once they finish a quarantine protocol.

Montana hunters killed 75 bison. Another 37 were shot by the Park Service or Montana Fish, Wildlife & Parks wardens after being wounded. Fifty-three bison were considered “unattributed harvests.” Eighty-eight bison were captured and shipped to slaughter with the meat given to tribes. Six bison died in the Park Service’s holding facility.

Due to the deaths, by May the bison population had fallen to around 3,960 animals, but the calving rate this spring was around 45 calves per 100 2-year-old females. The proportion of females, about 57%, is a 10-year high, the Park Service said.

“The status of the bison population illustrates its resiliency to removal of up to 25% of the population,” Geremia wrote.