WEST YELLOWSTONE, Mont. (AP) — Just over a dozen bison were killed or had to be euthanized after they were struck by vehicles on U.S. Highway 191 just north of the town of West Yellowstone, the western entrance to Yellowstone National Park, officials said.

West Yellowstone Police Chief Mike Gavagan said three vehicles, including a semitruck, hit the bison at about 6:30 p.m. Wednesday.

Some bison were killed in the collisions and others were put down due to the severity of their injuries, leaving a total of 13 bison dead.

No one in the vehicles was injured, NBC Montana reported.

It was dark at the time of the crash, making it hard for the drivers to see the bison. The animals’ eyes don’t reflect light like deer do, contributing to the difficulty in seeing them on the road, officials said.