Helicopters began rounding up wild horses Monday in northwestern Colorado over the objections of animal advocacy groups.
The U.S. Bureau of Land Management plans to gather about 140 horses it says have moved outside of public land designated for them.
Groups including the American Society for the Prevention of Cruelty to Animals sued last week to try to stop the roundup. The lawsuit, filed in U.S. District Court in New York, claims removing the horses violates environmental laws and the federal Wild Free-Roaming Horses and Burros Act.
BLM spokesman David Boyd said the contractor hired through Oct. 22 won't gather the estimated 60 horses in the North Piceance area at first because of the groups' specific objections to removing those horses. The agency wanted to see if a hearing would be scheduled in the lawsuit.
But Boyd said the BLM still plans to gather all the horses over the next few days.
The ASPCA appreciates the BLM's efforts to avoid the North Piceance area but still opposes the immediate removal of any wild horses, said Matt Bershadker, the group's senior vice president.
The horses will be herded into corrals. Those which are not sold or adopted will be taken to long-term pastures in the Midwest.
Animal advocacy groups have filed lawsuits trying to stop wild horse roundups across the West, calling them inhumane and unnecessary.
BLM officials have said the roundups are one of the few ways they have to deal with herds that get too big for the resources. Boyd has said the number of wild horses in northwest Colorado typically increases 20 percent each year.