Forty bison mill about on the football field at the school in Gardiner, Mont. One of the shaggy beasts rubs her head vigorously against the goalpost. A light snow is falling.

I walk over and sit on a nearby boulder. I feel that it is the least I can do -- just sit in the final presence of these animals that have moved into town. In January, I saw a herd of bison in the park circle as a pack of wolves approached. The bulls faced down the wolves and then escorted them out of the vicinity, like bar-bouncers whose mere countenance suggests the wisdom of departure.

At 22 below zero, I watched the steam rise from their nostrils as they disregarded the cold. A week later, they began to move. A previous warm spell had caused the snowpack to melt; then the return of freezing weather turned what lay on the field to ice. The bison, their massive heads no longer able to plow aside snow to uncover the grass, followed their hunger to lower ground.

In late February, the bison began to clog the roads. They ambled in an unhurried stream off the Blacktail Plateau, across the bridge over the Yellowstone River, down past Mammoth Hot Springs and into the schoolyard.

For weeks, the park radio cackled with frenzied rangers attempting to haze the bison back into the national park. But as one bison rancher told me, "You can get a bison to do whatever it wants to."

When bison insist on acting like wild animals and refuse to stay within the confines of Yellowstone National Park, they must be killed. That is the ruling of the federal Interagency Bison Management Plan. And because the park population of bison has risen over the maximum number of 3,000, the animals can be killed without being tested for brucellosis, the disease that led to the formation of the control plan for bison. Brucellosis can cause cows to abort and leads to sanctions against beef producers.

I watch as the bison begin to move past the school and onto the flats, where they are herded into the capture facility, joining another 50 from the previous day. Late in the afternoon the trucks will come.

The next day begins with a winter storm that postpones the next shipment, and 47 bison still remain in the pens. The area is closed by order of the superintendent and armed rangers guard the entrance as if it contained something precious. Just inside the park boundary, the capture facility consists of a fenced enclosure that funnels into three smaller pens where the animals are sorted into bulls, cows and calves. The sorting pens are lined with plywood to prevent the animals from injuring themselves or getting too excited as they are loaded into trucks that haul them to slaughter.

Mike Mease of the volunteer Buffalo Field Campaign wants to film what happens at the facility, and so park rangers Marsha Karle and Tim Reid have offered to escort our small group to the pens.

When I ask about why 3,000 was chosen as the magic number, Tim cites a study done by park biologist Rick Wallen. He says it suggests when the population approaches 3000, in combination with other factors such as water content in the snow, the bison begin to move. "The north wind gets them to move; they turn like a weather vane and head into the wind," says Tim.

From the causeway, we look down at the empty pens and the bison milling about the enclosure. We discuss the brucellosis issue, the fact that elk also carry the disease, how this has suddenly become a population-control issue, the notion of sport-hunting the bison.

But I want to get past the arguments and counter-arguments, past the details, past the reasoning, or lack thereof. It’s the fencing, corrals, chutes and pulleys I keep coming back to. I look north. The map tells me the park border is just ahead, yet the landscape is unbroken. Mountains rise unhindered to our left and right.

"Can this really be considered a free-ranging herd of bison?" I ask. Both Marsha and Tim look down. "You know, I won’t even use that term anymore," says Marsha.

"This hurts my heart so much, that here are these beautiful animals we can’t even save," says Mike, who has dedicated the last seven years of his life toward stopping the bison slaughter. We all stand gazing down at the bison as they move slowly through the pen, feeding on the provided hay.

Greg Gordon is a contributor to Writers on the Range, a service of High Country News in Paonia, Colorado (hcn.org). He lives in Gardiner, Montana, and teaches at the Yellowstone Institute.