GARDINER, Mont. — This was not the Yellowstone National Park that tourists see.
At first light on Tuesday, more than 60 of the park's wild bison were loaded on a semitrailer to be shipped to a slaughterhouse. With heavy snow still covering the park's vast grasslands, hundreds of bison have been leaving Yellowstone in search of food at lower elevations.
A record number of the migrating animals — 1,195, or about a quarter of the park's population — have been killed by hunters or rounded up and sent to slaughterhouses by park employees. The bison are being killed because they have ventured outside the park into Montana and some might carry a disease called brucellosis, which can be passed along to cattle.
The large-scale culling, which is expected to continue through April, has outraged groups working to preserve the park's bison herds, considered by scientists to be the largest genetically pure population in the country. It has also led to an angry exchange between Montana state officials and the federal government over a stalled agreement to create a haven for the bison that has not received the needed federal financing.
Al Nash, a spokesman for Yellowstone National Park, said park employees try to haze the bison into returning to the park but often meet with limited success.
"They come right back out again," said Gov. Brian Schweitzer of Montana. "They just rebel. What would you do if you were a starving buffalo?"
The culling of bison at Yellowstone, while legal, has been a briar patch of controversy for more than two decades. In 1996, the count reached a peak — until this year — when 1,084 animals were killed.
In 2000, Montana, the National Park Service, the U.S. Forest Service and the Animal Plant Health Inspection Service, which oversees disease issues for the Department of Agriculture, signed an agreement to manage the population.
The agreement had two main objectives. The first was to stop the spread of brucellosis, a bacterial infection that can cause spontaneous abortion in cattle and, when detected, requires the cattle be destroyed.
The second objective was to allow some bison to leave Yellowstone unmolested.
Conservationists, Montana state officials and other critics say the first part of the agreement has been honored, but the second part has been ignored by the federal government.
Federal officials say the money needed to make the agreement work — to obtain land along the Yellowstone River that would allow the bison to cross from the park to a publicly owned forest north of the park — has not been allocated by Congress.
In the meantime, conservationists and researchers who care about the bison worry that serious damage is being inflicted on the population.
Biologists have discovered that Yellowstone's bison are one of only two genetically pure herds owned by the U.S. government. James Derr, a professor of genetics at Texas A&M who is studying the Yellowstone bison, said he feared some behaviors or traits — including the propensity to migrate — could be lost with the killed bison.
"The great-grandmother, grandmother, mother and daughter often travel together," he said. Killing them "is like going to a family reunion and killing off all of the Smiths. You are affecting the genetic architecture of the herd."
In the next few weeks, the snow will start to melt and new grass will sprout in the park. At that time, some captured bison that test negative for exposure to brucellosis will be allowed back into the park. Those that test positive will be slaughtered.
"It's a very difficult thing," said Nash, the park spokesman, as he watched park employees load the bison for slaughter on Tuesday. "They do the job they have to do, but that doesn't mean they enjoy doing it."