at custer state park, the herd has grown, so it must be cold every year. the buffalo inspected and inoculated against infectious diseases, and then branded. so the animals can be tracked over time. craig pugsly helps to coordinate t. >> for us, it's management. we would do the roundup whether somebody showed up or not. we bring in the herd and we brand the calves, and we cut out the ones this we're going to sell in the fall auction. >> reporter: so the roundup is more than a spectator sport. it's a way to protect the buffalo, and that's why bob landis has volunteered over four decades. >> reporter: how long are you going to keep riding here? >> until the day i die. my goal is to be riding along and hit the ground dead as i fall off my horse >> reporter: chasing a buffalo? >> chasing a buffalo. >> >> reporter: now it has taken 100 years until the species is no longer in danger. a vivid reminder of what the country was so close to losing, and how the enduring symbol of the west prevailed in spite of a scandalous past. >> perfect, just ahead on america tonigh

at custer state park, the herd has grown so it must be culled every year.he buffalo inspected and innoculated against infectious diseases. then branded. so the animals can be tracked over time. craig pugsley helps coordinate the annual roundup now in its 48th year. >> for us it's a management tool. we would do the roundup whether anybody came or not. we need to bring in the herd and get an accurate count. we vaccinate the heifer calves for brucellosis and we cull out the ones we want to sell at the fall auction. >> so it's more than a spectator sport, it's a way to cultivate and protect the buffalo. >> how long do you want to keep coming? >> until i die, falling off dead chasing the buffalo. >> nearly 400,000 it has taken 100 years but the species is secure no longer in danger. the majestic animals here a vivid reminder of what the country came so close to losing and a stunning example of how the efforts to save an enduring symbol of the west last survived despite a scandal that passed. >> beautiful, our report from chris bury. >>> coming up next, a lab in