RENO, Nev. (AP) — A legal battle over the U.S. government’s ongoing capture of thousands of wild horses in Nevada where 31 mustangs have died in a weekslong roundup goes before a judge Wednesday as opponents try to prove it’s illegal and should be stopped.

Federal land managers said in new court filings ahead of the Reno hearing that the deaths among 2,500 horses gathered since July 9 are an unfortunate — but expected — part of necessary efforts to cull the size of large herds.

They said the free-roaming animals pose a threat to the ecological health of public rangeland.

Horse advocates said the deaths were unnecessary, resulting from inhumane tactics being used to expedite removals from public lands where pregnant mares and young foals are being chased in summer heat across rocky, high-desert into makeshift corrals.

U.S. District Judge Larry Hicks scheduled Wednesday’s hearing to get details from both sides as he considers the non-profit Wild Horse Education’s bid for a temporary restraining order halting the gather in northeast Nevada scheduled to run through Aug. 22.

Government lawyers said in court filings Monday the horse advocates are trying to inflame emotions with photos and videos of injured mustangs trying to flee helicopters and wranglers on horseback. One with a broken leg was chased for 35 minutes before it was euthanized.

“Deaths are tragic, but they are a known and anticipated part of wild horse gathers that must be weighed against the harm the same horses face under drought and overpopulation conditions if the gather cannot be completed,” Justice Department lawyers representing the bureau wrote.

The agency says the 31 deaths are within the average mortality rate of 1% and 1.2% for wild horse gathers conducted from 2010-19.

“Plaintiffs list the number of deaths that have occurred during the gathers but fail to mention the thousands of horses that have been gathered safely,” government lawyers wrote.

“Despite plaintiffs’ sensational allegations, there is nothing out of the ordinary ... and nothing to suggest the conditions of these gathers have been unusually dangerous to the horses,” they added.

Horse advocates said the mustangs have been made scapegoats for damage most-often caused by taxpayer-subsidized cattle grazing the same limited forage on the high-desert range at much higher numbers.

Among other things, they said in a lawsuit filed July 26 the roundup halfway between Reno and Salt Lake City is illegally based on an outdated environmental review that fails to reflect current conditions on the range. They said it also ignores evidence the herds are still in the midst of foaling season when the use of helicopters is largely prohibited.

Democratic U.S. Rep. Dina Titus, of Nevada, is pushing legislation in Congress to outlaw the use of helicopters altogether.

The lawsuit also claims the agency is failing to comply with requirements that the public be allowed to witness the roundups, frequently parking trucks and trailers to obscure distant views from the designated observation area.

Above all, the lawsuit argues the roundup violates a 1971 U.S. law that mandates that the animals be treated humanely.

“The physical and emotional toll of watching BLM wrap abuse in layers of bureaucracy and simply take no real action to stop inflicting unnecessary suffering on these sensitive and family-oriented beings is sickening,” said Laura Leigh, founder of the Nevada-based Wild Horse Education.

Leigh says the bureau has erroneously concluded that peak foaling season is the same for all herds — from March 1 through June 30. During this period the agency grounds helicopters to minimize potential harm to the young foals.

Leigh said she’s documented seasonal distinctions throughout western rangelands in 10 states. She said some begin as early as late January and others continue through September.