“Thirteen bison were killed in this traffic accident, with some of the bison needing to be euthanized due to severe injuries,” said the West Yellowstone Police Department in a news release posted to Facebook on Friday.“Please do not drive faster than you can stop within the distance that your headlights project.”Officials initially thought multiple vehicles were involved, but after “further and thorough investigation,” police determined that all 13 bison were struck by the semi-truck.Yellowstone National Park is home to a population of bison that fluctuates from between 2,300 to 5,500 animals, according to the National Park Service.The species, named the national mammal in 2016, is now flourishing in Yellowstone National Park after dedicated conservation, breeding, and reintroduction efforts.The Yellowstone bison are managed through a federal-state agreement that seeks to protect the population while also preventing them from spreading a bacterial infection called brucellosis to Montana cattle."