RENO, Nev. (AP) — A judge has asked federal land managers to explain why they should be allowed to continue capturing more than 2,500 wild horses in northeastern Nevada — a roundup opponents say is illegal and has left 31 mustangs dead in 26 days.

Wild Horse Education, a nonprofit seeking to protect the horses, has sued the Bureau of Land Management and is seeking a court order to temporarily halt the roundup halfway between Reno and Salt Lake City.

Among other things, it says the agency is violating its own safety standards that prohibit roundups in extreme heat and the use of helicopters to assist in the capture of the animals when foals are present.

More than 260 foals are among the 2,643 animals that have been rounded up for transport to government holding pens since July 9, the agency said on its website Saturday. Several-hundred more are expected to be gathered before the roundup ends Aug. 22.

Democratic U.S. Rep. Dina Titus, of Nevada, has introduced a bill that would outlaw the use of helicopters under any circumstances to assist wranglers on horseback chasing the mustangs into traps — makeshift corals on the high-desert range.

She urged the chairman of the House Natural Resources Committee this week to expedite a hearing on her proposal due to the horse deaths, including one with a broken leg that was chased for 35 minutes before it was euthanized.

“Despite BLM’s directive to `humanely capture’ wild free-roaming horses and burros ... the use of helicopters routinely creates frightening and deadly situations for horses as demonstrated in recent weeks,” Titus said.

“These horses have suffered through a host of tragic injuries, ranging from broken necks, broken legs and even dehydration due to the oppressive triple digit heat,” she wrote in a letter to the committee chairman, Republican U.S. Rep. Bruce Westerman, of Arkansas, and ranking U.S. Rep. Raul Grijalva, D-Ariz.

“Without meaningful reforms, BLM’s operations will continue to kill off these icons of the West in completely avoidable circumstances,” she wrote.

So far, U.S. District Judge Larry Hicks in Reno has declined to grant the Aug. 1 request for a temporary restraining order to halt the Nevada roundup. But on Friday, he put the agency on notice it has until 4 p.m. Monday to formally respond to the allegations of illegal mistreatment of the animals.

He set a hearing for Wednesday to hear more detailed arguments if necessary from lawyers on both sides.

Nevada is home to nearly two-thirds of the 68,928 wild horses the bureau estimated on March 1 were roaming federal lands in 10 Western states stretching from California to Montana.

The bureau said in a court filing Wednesday that its latest roundup, which began July 9 between Elko and Ely near the Utah border, is a “crucial gather” because overpopulated herds are seriously damaging the range.

It said the estimated 6,852 horses there is nearly 14 times what the land can ecologically sustain. It says roundups typically have a mortality rate of less than 1%.

Critics say the real purpose of the removals is to appease ranchers who don’t want horses competing with their livestock for precious forage in the high desert, where annual precipitation averages less than 10 inches (25 centimeters).

Wild Horse Education’s motion for a temporary restraining order says there’s no legitimate reason to conduct the current roundup in extreme heat with helicopters when foals are present, “especially when the BLM has plenty of time to conduct this gather in a humane manner as the law requires.”

“Without injunctive relief, plaintiffs will continue to be permanently and irrevocably harmed in witnessing the atrocious and horrific sights of wild horses and burros dying due to the inhumane handling, extreme heat and use of helicopters during foaling season.”