RENO, Nev. (AP) — In a rare legal victory for wild horse advocates, a judge has ruled U.S. land managers failed to adopt a legal herd management plan or conduct the necessary environmental review before 31 mustangs died during the roundup of more than 2,000 horses in Nevada last summer.

U.S. District Court Judge Miranda Du in Reno ordered the Bureau of Land Management to complete a formal herd management plan for the Pancake complex in eastern Nevada by next March 24. She also ordered the agency to reopen an environmental assessment to include the potential impact of roundups on wildfire risks.

Du specifically rejected the argument the agency has made for years that its broader resource management plans combined with individual roundup plans for overpopulated herds satisfies the requirement that it adopt a formal herd management area plan (HMAP) for the long-term health of the herds and the rangeland in a particular area or herd complex.

“The court finds that BLM must be compelled to prepare a herd management area plan (HMAP),” Du wrote in the 29-page ruling issued Thursday.

Horse advocates who cheered the ruling said that while it comes too late for the horses that were captured or killed last summer, it sets a precedent that will help provide more protection for mustangs roaming federal lands in the West going forward.

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“This is an amazing day for our beloved wild ones.” said Laura Leigh, founder and president of the lead plaintiff in the case, Nevada-based Wild Horse Education.

“The Wild Free-Roaming Horses and Burros Act is about more than just removal. Today, the court affirmed the intention of that law,” she said Friday.

A spokesman for the Bureau of Land Management said Friday the agency was reviewing the ruling but had no immediate comment.

Last summer, another U.S. judge in Reno refused to grant an injunction sought by horse advocates to halt the roundup that was underway after dozens of horses died during the roundup.

Judge Larry Hicks concluded in August the agency had not violated laws protecting the animals from inhumane treatment. But he allowed Wild Horse Education to continue with the lawsuit it first filed in 2022 that alleged the agency was acting illegally because it never implemented the herd management plan that was required since the management area was established in 1986.

Du did not address allegations of inhumane treatment of the animals. She agreed with the agency’s argument that it had the authority to round up horses as soon as it determined the herd was overpopulated. And she rejected horse advocates’ attempt to force the agency to specifically consider cutbacks in livestock grazing or incorporate different procedures to estimate the sizes of herds.

But Du said the bureau could not continue to respond to lawsuits by explaining it was still in the process of completing a formal herd management area plan (HMAP) with no definitive assurance it actually would complete one.

“The duty to prepare an HMPA arose as soon as the BLM created the HMAs,” Du wrote. “That duty arose when BLM promulgated the regulation 38 years ago in 1986. BLM’s decades-long delays in developing and approving HMAPs have therefore been ‘nothing short of egregious’ and clearly violate the rule of reason.”

Leigh said that, among other things, the agency’s failure to complete the plan denied the public a chance to address how forage is divided between horses and livestock, herd genetics can be preserved or mitigation measures can be adopted for mining and livestock expanding in the area.

“For over 12 years I have been trying to address critical issues of on-range management planning with BLM and have been repeatedly denied,” Leigh said. “This ruling has finally opened the door to advocacy and actually has the opportunity to engage in management practices.”