Bison advocates are decrying this month's hazing of bison back into Yellowstone National Park, but officials of the agencies involved in the work say they've been more lenient than ever before.

"We had a great deal more tolerance for bison outside the park boundary this year," said Al Nash, Yellowstone's chief of public affairs. "But there are still limits for bison outside the park boundary."

Although bison are being hazed, he noted that none are being captured and shipped to slaughter. And bull bison that are not in mixed groups are allowed outside the park year-round.

Bison advocates argue that the animals should be allowed to remain west of the park on Gallatin National Forest and 800 acres of private land designated a "safe zone" on the Horse Butte peninsula.

"Horse Butte is different from other areas near the park," said Matt Skoglund of the Natural Resources Defense Council in Livingston. "There are literally no cows there. To haze them, when there's no threat and no conflict, makes no sense."

Under the rules of the federal-state Interagency Bison Management Plan, the Montana Department of Livestock is the lead agency responsible for hazing bison back into the park. There is a May 15 deadline to accomplish the task.

"We work to provide a month between the time the bison are on the land and the cows are expected to graze," Nash said.

The month between bison occupation and the return of cattle is to allow any brucella that bison may have transmitted to the ground, possibly through birthing materials, to die off.

Since last week, Department of Livestock officials have used herders and a helicopter to haze bison back into the park along the south side of the Madison River, according to Stephany Seay of Buffalo Field Campaign, a bison advocacy group that monitors the work. This week, she said, Park Service, Gallatin National Forest and Fish, Wildlife and Parks personnel have helped from horseback.

Bison advocates complain that elk have been implicated as the most likely vectors in some of the recent transmissions of brucellosis to cattle, yet they are not subjected to the same controls as bison.

They also note that state and federal agencies last year agreed to spend $3.3 million to acquire a 30-year lease for grazing rights near Yellowstone's northern border near Gardiner. The lease allows only 25 bison that have been tested and are free of brucellosis to roam through a portion of the Royal Teton Ranch to forest land. Meanwhile, the owners of the 800 acres on Horse Butte are offering a free haven for bison.

No bison migrated north of the park this past winter and none were slaughtered. More than 1,600 were slaughtered the year before, most of them at the north end, under rules of the Interagency Bison Management Plan. The current park bison population is estimated at 2,900.

Contact Brett French at french@billingsgazette.com or at 657-1387.