The Texas-based Habitat for Horses, New York-based American Society for the Prevention of Cruelty to Animals, the Colorado-based Cloud Foundation and two Colorado residents filed a lawsuit Thursday in U.S. District Court in New York. The groups claim the plan by the U.S. Bureau of Land Management to remove an estimated 138 horses violates environmental laws and the federal Wild Free-Roaming Horses and Burros Act.
It wasn't clear Friday when a hearing in the lawsuit might be scheduled.
"We're continuing forward with the gather (of horses). These gathers have been challenged before," Colorado BLM spokesman David Boyd said.
The horses that will be rounded up are outside a 190,000-acre area of public land designated for wild horses, Boyd said.
The agency has hired a contractor through Oct. 22 to use helicopters to herd the horses into corrals. Boyd said it could take several days because the horses are roaming the countryside in small groups.
Horses not sold or adopted will be taken to long-term pastures in the Midwest.
The groups suing didn't immediately return messages Friday. They contend in their lawsuit that the BLM hasn't properly determined if there are too many horses in the area.
The lawsuit also claims the plan to remove the animals violates the 1971 wild horse act's requirement to preserve the horses in their range and the requirement under federal environmental laws to consider reasonable alternatives.
The 1971 laws' clear mandate "has been that federal agencies must protect these national icons and allow them to remain on the land which they have called home when that law was originally drafted," according to the lawsuit.
Animal advocacy groups have filed lawsuits trying to stop wild horse roundups across the West, calling them inhumane and unnecessary.
Boyd declined to respond to specific claims in the challenge to the Colorado roundup. He said the roundups, carried out in the state since the 1980s, are the only effective way of controlling the horse population, which typically increases 20 percent each year.
"Wild horses don't have natural predators. They're not native wildlife," Boyd said. "The only natural controls are starvation and disease."
The public land designated in northwestern Colorado for wild horses is also supports wildlife, livestock grazing, recreation and other uses, Boyd said.
Next year, the BLM wants to remove about 100 horses that were separated from the main herd by a highway expansion.
The agency also wants to reduce the number of horses in the designated area. The herd numbers 318 and the preferred size, considering the resources is from 135 to 235 horses, Boyd said.