It could have been a scene from the Old West - hundreds of brown buffalo thundering across the South Dakota prairie.
The roundup in South Dakota's Custer State Park of nearly 1200 free-ranging bison drew 14000 spectators as cowboys on horseback, helped by drivers in sport utility vehicles, corralled the animals on Monday so that they could be counted and vaccinated.
"It's a thrill to see all those buffalo move at one time," said Keith Goodhope, a businessman who doubled as a cowboy for the drive. "It's every South Dakota boy's dream."
Custer Park officials manage what is considered to be among the largest publicly owned bison herds in the world.
Buffalo have a long history in the region and were part of the foundation of the culture of the Lakota Sioux Indian tribe, which once flourished in the area.
The roundup in the state park started 45 years ago as a way to manage the size and health of the animals, which can stand 1.8m tall and weigh up to 900kg.
The 29000ha park typically has the capacity to care for about 1500 free-roaming bison, but the size of the herd has declined over the last few years because of drought that reduced the availability of grazing.
Now park managers said they can start growing the herd back to capacity, thanks to plentiful rains that have restored lushness to prairie grasses.
"That's always our target," said Craig Pugsley, spokesman for Custer State Park and a veteran of annual buffalo roundups.
Sacred to American Indians and a symbol of the American West, bison once numbered in the millions but were hunted to near extinction in the 19th century. They were hunted to make room for railroads and farms, and for fur.