Roughly 500 to 600 bison that migrated out of Yellowstone National Park during the winter are back on their summer feeding grounds, after being hazed into the park by state and federal personnel.

Only one migrating bison was killed this winter, by a Montana hunter.

The previous winter about 1,600 bison were killed, most of them captured and slaughtered during migration to prevent the spread of the disease brucellosis to cattle.

Christian Mackay, the head of the Montana Department of Livestock, says the hazing lasted about two weeks and pushed the bison into an area about 15 miles inside the park.

Brucellosis causes pregnant animals to miscarry. About half of Yellowstone bison test positive for the disease, but there have been no recorded transmissions from the animals to cattle.