On the buffalo trail at Antelope Island

Cody, an Army scout and Pony Express rider, killed thousands of bison to provide meat for workers on America's expanding railroads in the mid-1800s. Back then, millions of buffalo roamed the plains from Mexico to Canada -- so many that the pounding of their feet echoed like rolling thunder. When herds crossed railroad tracks, trains were delayed for up to half a day. The railroad companies responded by allowing passengers to shoot the buffaloes from the rail cars.

"The moving multitude . . . darkened the whole plains," wrote Meriwether Lewis, who along with William Clark encountered a herd at South Dakota's White River in 1806.

But in a few short decades, American Indians, hunters such as Cody and others slaughtered so many buffaloes that the once-thriving herds dwindled to only 800 animals. Shamed at the widespread massacre, Cody later in life joined efforts to preserve the namesake animal he became famous for hunting.

Eventually, preservation efforts rescued the bison from the brink of extinction. Today, about half a million bison roam public and private lands across the country; the biggest herd, about 4,000 bison, grazes in Yellowstone National Park. (The terms "bison" and "buffalo" are used interchangeably, although biologists note that the American bison is only distantly related to the water buffalo and African buffalo.)

Antelope Island's bison are descendants of a dozen buffaloes brought by barge by ranchers William Glassman and John Dooly in 1893. With plenty of grazing land and spring water, the bison thrived. When the state took over the island, park officials invited the public to take part in the annual roundup. Each year, for the last 22 years, the bison are herded into pens so veterinarians can perform medical tests, administer vaccinations, collect blood and check the cows and heifers for pregnancies. To ensure the population does not exceed the island's food supply, some are sold at auctions. The state also sells handful of hunting permits -- about six -- to cull the older bulls that are too ornery to herd or put in trailers.

For the roundup's first 19 years, state park officials relied heavily on helicopters to herd the bison. But the helicopters put too much stress on the bison, so in 2005 officials turned over the roundup reins to volunteer riders -- nonprofessionals like me.

::

The night before the roundup, I shivered in a tiny tent on a lumpy grass field near Fielding Garr Ranch, the horse rental concession on the south end of the island.