LAS VEGAS - A two-month capture of about 2,500 wild horses from public and private lands in northern Nevada began yesterday amid protests that the roundups are unnecessary and inhumane.

Federal officials said the roundup was needed because the 850 square miles of land is overpopulated and could become unlivable to wildlife and livestock within four years.

Bureau of Land Management spokeswoman JoLynn Worley said the agency began gathering horses in the eastern portion of the Black Rock Range, a stretch of mountains more than 100 miles north of Reno.

A contractor was using two helicopters under BLM supervision to move the horses to corrals, Worley said. The animals were then being trucked to Fallon, Nev., for immunizations and veterinary care, she said.

Worley said officials would not know until early today how many horses were captured yesterday. She said the agency would probably be in the range for one week to 10 days - with a goal of capturing 250 mustangs - before moving on to the next of five areas.

Long-term plans call for the mustangs to be placed for adoption or sent to holding facilities in the Midwest. The agency said a facility in Reno was full of adoptable horses, making it unclear when the animals gathered in the latest capture could be put up for adoption.

Horse defenders say the use of helicopters to drive horses to corrals is inhumane and risks their injury and death. Opponents also contend that winter roundups expose horses to the risk of respiratory illness.

Suzanne Roy, program director of In Defense of Animals, said the group questioned the timing of the roundup and methods that prevent public monitoring of the roundup.

"It just all smells bad," she said. The California-based group has had trouble getting White House and other federal officials to work through their complaints during the holidays, she added.