WOLF POINT — Everybody heard the trucks before they saw them. The sound of engines and tires on dirt roads made them look. Dust clouds became visible, and then the caravan rounded a corner, drove past a shed and through an open gate.

The six trucks and trailers made a wide arc in the double-fenced pasture and lined up, pointing the trailer doors southwest. Inside each one were three bison in individual compartments, all ready to run.

Four men beat drums and sang a traditional song to welcome the animals home. A few dozen people gathered around, many of them government and tribal officials who dreamed this day would come, sometime. A few spectators sat on cars outside the fence.

Then the doors were opened and the bison started running out, exploring their new home.

“These are the Yellowstone buffalo,” one of the spectators said.

The animals had been loaded into the trailers early Friday morning at the park’s corrals near Gardiner. After several hours, a truck breakdown and some 450 miles, they became part of the first group of bison ever transferred directly from Yellowstone National Park to the quarantine corrals on the Fort Peck Indian Reservation.

“Now we’re seeing the fruits of our labor,” said Robbie Magnan, the fish and game director for the Fort Peck Tribes.

Friday’s was the third caravan of trailers to come here this week, bringing a total of 55 bison to the reservation. Park officials tried to keep the move quiet because they worried about sabotage from opponents of quarantine, but they invited people to watch the final group step off the trucks.

So bison advocates and a few dozen federal, state and tribal officials gathered in the middle of the prairie here to watch these bison sprint into the corrals where they’ll spend the next year. Among the crowd was former Yellowstone chief Dan Wenk, who was running the park when quarantine was proposed, and longtime Yellowstone bison biologist Rick Wallen, who retired last year.

They watched the bison run, ate meatballs and celebrated a milestone for quarantine, which is meant to produce disease-free animals that can be moved elsewhere to boost existing herds or start new ones. Supporters and the government officials behind the program hope what they saw Friday is just the start.

“Hopefully, we’re opening the door to doing quarantine into the future,” said Chris Geremia, a Yellowstone biologist.

The idea is to certify bison as free of brucellosis, a disease transmitted through afterbirth that can cause animals to abort their calves. Once a public health concern, the disease is feared by livestock producers that worry its spread could disrupt the industry.

The disease has mostly been eradicated, but bison and elk in the Yellowstone region are known to carry it. Although there’s never been a documented case of bison giving the disease to cattle in the wild, the fear of transmission has driven bison management.

A management plan for the bison limits where the animals can go and calls for population control, which is accomplished through annual hunts and a ship-to-slaughter program.

Quarantine provides a way for bison to be culled from the Yellowstone population without being killed. Once the bison are deemed disease-free, they can be moved without any fears of disease transmission.

Fort Peck has received disease-free bison in the past, but always after the bison spent considerable time somewhere other than Yellowstone. The reservation has a cultural herd of about 340 now and a business herd of about 250. But the tribes want to become a source of bison for other tribes around the country, such as the five they sent to the Wind River Reservation in May.

Yellowstone National Park proposed quarantining bison here in the rolling hills between Poplar and Scobey in 2016. The tribes had spent $600,000 building the corrals here. But legal and political roadblocks stalled that idea, forcing supporters of quarantine to pivot.

Instead, Yellowstone turned two corrals at its bison trap northwest of Gardiner into a quarantine facility. It captured bison and began testing them for disease. Some of the bison were almost ready to be moved to the reservation in 2018 until they were set free by vandals who cut a hole in the quarantine fence. Park law enforcement investigated but never found the culprits.

Not long after the fence was patched, the park started capturing bison again and set aside about 80 for quarantine, including the 55 moved this week. A few months later, the National Park Service formally signed off on a quarantine plan that called for two rounds of testing near Yellowstone and a final round that could take place at Fort Peck.

They want to be able to do the second round of testing at their place, something federal agriculture officials have balked at so far because they worry it poses too much of a disease transmission risk.

Chamois Anderson, of the nonprofit Defenders of Wildlife, said her group is working to get a meeting with Agriculture Secretary Sonny Perdue to help the tribes make the case they should be approved for the second round of testing. That could increase the number of bison moving through quarantine, which is something she and many other wildlife advocates want.

“The idea is that Fort Peck will be a clearinghouse,” Anderson said.

But Cam Sholly, Yellowstone superintendent, said Friday that the corrals here are already helping bison. Without the Fort Peck corrals, the 55 bison would have had to stay in the park another year or potentially go to slaughter. Instead, the shipment frees up space for the park to capture more animals for quarantine this winter.

“In many ways, this facility is playing a critical link,” Sholly said.

More may soon be on their way here, too. The tribes expect to get 33 female bison from the USDA corrals this winter, and the park is still holding 22 female bison they hope can be moved here in about a year and a half.

The 55 that came this week follow a group of four bulls already in one of the tribes’ quarantine corrals. The four bulls are expected to graduate the final testing round in October, making room for new arrivals.

The ones that came this week will be tested in January and May, Magnan said. By the time it’s over, he hopes they’ll have a place to go — maybe to another Native American tribe.

“Two more tests and they’re OK,” Magnan said. “They’ll be going to their new homes.”

Michael Wright can be reached at mwright@dailychronicle.com or at 406-582-2638. Follow him on Twitter @mj_wright1.

Michael Wright covers the environment and wildlife issues for the Chronicle.

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