“The whole bridge is just jumping.”
There are many reasons to be unnerved by a herd of bison trotting past your vehicle but the kinetic force generated making an entire bridge to shake is a new one to me. Check out this video from last Friday of a gang of bison making their way over the Yellowstone River causing the entire structure bounce. Thats a lot of biomass indeed. I wonder if any of the parks siesmographs ever get triggered by bison?