Cars are slowly driving everywhere and if you see them pulled off the road, follow them; there's wildlife in sight. Unfortunately, some people try to get too close and/or are too loud, and the animals get spooked.
There's a wild herd of bison that is annually "rounded-up" for medical checkups and for a grand tourism spectacular. We did not make the 5:30ish a.m. start time but did check out the area a few hours later. Hundreds of cars were heading the opposite way and we finally arrived at the "pen" area.
Here's the dark secret of the western round-up. Before the
bison, cowboys, and cowgirls ride up over the hill for the tourists,
pickup trucks have driven through the park, scaring the animals
and funneling them towards the pens. Ah well. It's a beautiful place
in spite of this subterfuge and the park's namesake.
Visit if you have the chance.