ANTELOPE ISLAND — Instructions were simple enough: Watch the tail. If it comes up, stop, turn and slowly ride away. Otherwise, stay in the saddle and herd the buffalo to their annual physical.

Roughly 150 riders gathered at the Fielding Garr Ranch on the eastern shores of Antelope Island a few weeks ago. It was the start of the annual buffalo roundup.

Once a year, the island buffalo, about 750 head, are pushed from their grazing areas to the holding corrals on the northern tip of the island.

The work was once done by helicopter, and horses and riders were simply there to pick up stragglers. Three years ago, the helicopters were grounded and the entire roundup was put in the hands of the wranglers.

Once corralled, the buffalo rested, fed on fresh-cut hay and then patiently waited for the doctors to make their island call.

It took three days to round up most of the buffalo. The larger bulls, because of their weight — upwards of 1,800 pounds — and temperament, for the most part, were left alone.

Then, for a week, they rested.

Over the final four days, the buffalo were cut into small groups and pushed into a long chute, which eventually led to the ultimate "hugging" machine — mechanical arms that closed in around the buffalo and held them firm while veterinarians, where called for, drew blood, gave vaccinations and checked for pregnancy in cows.

More than 200 calves were born on the island last year, which is by all accounts a high birth rate for a free-roaming herd.

What vets found, as expected, is that the island herd is in good shape.

"Even their parasite count was low this year," said Steve Bates, island biologist for the Utah Division of Parks and Recreation, overseers of the island.

"Some years it's low. This is one of those years."

Each of the resident bison has a chip embedded behind the ear that, when scanned, gives a complete medical history. Some of the new calves were given chips to begin their medical background.

The island can comfortably hold a bison population of around 500 animals. To keep within that range, some animals are cut out and sold at auction. Money raised is used to improve things like habitat for wildlife.

Island bison have, in recent years, become popular with bidders, which has not always been the case.

"A few years ago, the market crashed," recalled Bates. "There had not been a meat market established at the time. I started beating on doors. I knew people here in Utah put a lot of meat in the freezer, so I started marketing to individuals. That's where a lot of the buffalo go now."