The Animal Protection Institute says 150 buffalo from Yellowstone National Park have been killed since November by Montana hunters in "the most atrocious big-game massacre in years."

The Sacramento-based organization, which claims 150,000 members, is calling on Montana's new governor, Stan Stephens, to halt the shootings. The animals are being killed as they wander out of the park in search of food, the group says.API Executive Director Duf Fischer said 300 buffalo were predicted to die this winter anyway from starving and hardship.

He said the combination of these deaths with the hunting of animals that are leaving the park in the wake of last year's drought and fires is "a full-fledged disaster in process."

Bruce Webb, API's program director and a biologist, said this is "no time to stand on the idea that nature must take its course and the buffalo population be decided entirely by the elements. How could it be? You don't have nature taking its course when buffalo trained all their lives to think that humans deliver no harm rumble out of the park with no idea the rules have changed - and they advance into waiting guns."