Wild mustangs. (Environmental News).

Forty-six thousand untamed horses roam Western rangeland. Wild mustangs--descended from horses of explorers, Native Americans, and pioneers--are symbols of the Wild West. But with no natural predators, the herds quickly swell to numbers unhealthy for both the horses and their habitat--their populations can double every three and a half years.

Of 260 million Western acres, 35 million are available to wild horses, says the US. Bureau of Land Management (BLM). To control the mustang population, the BLM herds surplus horses into temporary corrals, then offers them up for adoption. Scientists are also working on birth-control methods to decrease the wild-horse population. The BLM hopes to reduce the mustang herd to 24,000 by 2005.

Why thin mustang herds when around 4 million cows can graze on federal land? "Ranchers don't want wild horses eating the same grass they want to give cows and' sheep," says Jay Kirkpatrick of Zoo Montana in Billings.

Ranchers pay the U.S. government for the right to graze cattle on public land. Says Jason Campbell, spokesperson for the National Cattleman's Beef Association: "We think there's room for both [cows and horses]. But if you've got areas with too many grazing animals, the ecosystem suffers."

Meanwhile, roundups will continue. "If you're out West and you see wild horses running through, it's very cool," Campbell continues. "But it's not cool when you see a 50-horse herd that should have 13 animals, and the horses are nothing but skin and ribs and bone. It all goes back to how much range is out there for then."