Hundreds of bison in Yellowstone National Park are dying by "firing squad" this winter because the U.S. Park Service is shirking its duty to protect them, the director of an animal-protection group says.

"This is an unprecedented massacre," Wayne Pacelle, executive director of the Fund For Animals, said during a recent stop in Boise. The national organization has about 1,000 Idaho members.Because of the fires that ravaged Yellowstone National Park last summer, large numbers of bison and other animals are leaving the park in search of food.

Once bison leave park boundaries, Montana law allows hunters to shoot them to prevent the spread of brucellosis from infected bison to cattle on ranches surrounding the park.

The Fund For Animals doesn't buy the brucellosis argument.

"We think it's a ruse. There's never been a case in the wild of bison transmitting brucellosis to cattle, and we feel that even if this were a legitimate concern, it could be dealt with on a nuisance basis, as are wild animal problems in general," Pacelle said.

Since January, hunters have killed about 550 animals in a herd of 800 to 900. Last year, only 39 bison were shot outside the park, he said.

"These are the same bison that clog traffic in Yellowstone as sightseers snap photos of them," Pacelle said. "These animals are accustomed to a non-threatening, non-harmful human presence. And they're simply like dairy cows being shot."