Bison Slaughter, Stephens Creek Bison Capture Facility

In this file photo, National Park Service wildlife biologists take a blood sample from a wild bison March 1, 2017 in Yellowstone National Park.

Three activists were arrested Tuesday in Yellowstone National Park for attempting to block the slaughter of Yellowstone bison.

Two people locked themselves inside the squeeze chute at the park’s Stephens Creek corrals early Tuesday morning. The chute is where bison are readied for slaughter. Other protesters were also there, holding signs signaling their opposition to the annual cull of Yellowstone bison.

Park spokeswoman Vicki Regula said in an email that park rangers saw the two people at 5:30 a.m., and that the two were arrested at 12:30 p.m., for entering the area around the corrals. The area is closed to the public. No damage was done to the facility, Regula said.

A third person has also been arrested. It’s not clear why.

The three activists are connected to a group called Wild Buffalo Defense. On its Facebook page, the group calls itself a “collective of indigenous and non-native organizers dedicated to seeing wild buffalo roam free on the plains.”

The group has identified the three people who were arrested as Cody Cyson, Thomas Brown and Hannah Ponder. A clerk at the U.S. District Court in Yellowstone confirmed that three people were in custody and said initial appearances were scheduled for Wednesday.

In a phone interview, Adam Luke, a spokesman for Wild Buffalo Defense, declined to say how many people are involved in the group or how long it had been active. He described it as an “autonomous grassroots group” and said they wanted to intervene in the annual slaughter of bison “directly and nonviolently.”

“The main point of this action was to draw attention to the fact that there’s really minimal numbers of wild buffalo being kept in the park,” Luke said.

Yellowstone National Park had not issued a statement on the issue, and park staff had not returned a request for more information before deadline Tuesday.

Yellowstone works with other federal, tribal and state government agencies to reduce its bison population each year. A management plan calls for a population of about 3,000. Last August, Yellowstone biologists estimated the population at about 4,800 animals.

The reduction comes through slaughter and hunting. Last year, more than 1,200 bison were culled. This past winter, managers agreed to try to remove between 600 and 900 bison.

According to Montana Fish, Wildlife and Parks, hunters have taken an estimated 200 bison so far. The park had captured at least 350 bison as of late February. A park spokeswoman declined to offer detail Monday on how many of those bison had been shipped to slaughter.

The Buffalo Field Campaign, an advocacy group that watches bison management closely, estimates that the park has captured more than 500 bison so far this year and that more than 150 have been shipped to slaughter. The park did not respond to a question about the accuracy of those numbers before deadline Tuesday.

In a press release, the Buffalo Field Campaign signaled solidarity with Tuesday’s protest. One of those arrested — Thomas Brown — was a former field campaign volunteer.

Stephany Seay, a spokeswoman for the field campaign, said in the release that they applaud “these courageous souls for sacrificing their freedom to free wild buffalo and to draw more attention to this atrocious trap.”

“This action should send another strong message to Yellowstone National Park that there are many people who strongly oppose the current mismanagement of this American icon,” Seay said.

Tuesday’s arrests come after two previous break-ins at the facility this year. In those instances, someone cut fences to let bison walk free. Separate criminal investigations into each incident are ongoing.

There have been other attempts to block the slaughter of bison. A man was arrested in 2014 for chaining himself to a barrel to prevent trucks from taking bison to slaughter. After several hours, he and the barrel were removed and the trucks hauled bison away.

Michael Wright can be reached at mwright@dailychronicle.com or at 582-2638. Follow him on Twitter @mj_wright1.