Yellowstone National Park has captured roughly 150 migrating bison in recent days as officials step up efforts to reduce the animal's population under a 2000 agreement with the state of Montana.
Park spokesman Al Nash said Thursday that 53 of the captured bison had been transferred for slaughter or for use in animal contraception experiments. More shipments are expected in coming days.
Wildlife advocates accuse the park of baiting the animals after dozens walked into a capture facility near Gardiner on their own.
Nash says the park is feeding the animals it captures but is not baiting.
The agreement with the state is based on worries about a disease carried by bison. It calls for maintaining Yellowstone's bison herds at about 3,000 animals. There were 4,600 at the end of last summer.