Thousands of bison are free to roam across 40,000 acres at the Tallgrass Prairie Reserve near Pawhuska, Oklahoma.
Once a year, the bison are rounded up 500 at a time for herd maintenance. They get their shots, they're weighed, and tagged. It's a way to keep track of them, and to make sure they all stay healthy.
The Tallgrass Prairie Preserve is the largest protected remnant of tallgrass prairie left in the world, and is thriving because of the free-roaming bison.
The herd started with 300 bison in 1993, and is now up to more than 2,700.