A federal judge has ruled that the National Institutes of Health (NIH) violated the law when it determined that former research chimpanzees in New Mexico would not move to a sanctuary in Louisiana known as Chimp Haven.

After the NIH stopped supporting invasive biomedical research on chimpanzees in 2015, it started transferring chimps from research centers to Chimp Haven, a 200-acre property with a staff of dozens who care for more than 300 chimps.

Primates at this federal sanctuary tend to live in larger social groups than chimps do at research facilities, and have access to natural forests.

Some chimps, however, were deemed by the NIH to be too sick and frail to make the move. Officials noted that being trucked to a new home can be a stressful change for older animals that have spent decades living in one familiar place.

In October of 2019, the NIH announced that dozens of chimps would not be leaving the Alamogordo Primate Facility (APF) in New Mexico for that reason.

The Humane Society of the United States and other groups challenged this decision, saying that a law passed in 2000 as the CHIMP act required that the APF chimps be given the opportunity to retire at Chimp Haven and that the NIH did not have the discretion to declare them ineligible to go.

In the court ruling, Judge Lydia Kay Griggsby noted that that Congress, in passing the CHIMP act, understood that older and sicker chimpanzees would enter the federal sanctuary system.

"The Court recognizes and appreciates the difficult policy and practical considerations that NIH must confront in determining how best to ensure the health and safety of the frailest APF chimpanzees," the judge wrote. "But, the method appropriate avenue for resolving these important concerns is to pursue these matters with the appropriate policymakers within the legislative branch."

What happens next isn't clear.

Kathleen Conlee, vice president of animal research issues for The Humane Society of the United States, told NPR in an email that the judge saw the language of the law as "plain and unambiguous."

"In our view, NIH should immediately initiate plans for transferring the chimps as soon as practicable," Conlee wrote, noting that this lawsuit applies specifically to the chimps at APF.

A spokesperson for NIH said that the agency "does not comment on litigation."

A deadline of January 13 has been set for the plaintiffs to file a report to the court on the specific relief they are seeking, according to Leslie Rudloff, an attorney who works with Animal Protection New Mexico. She says animal welfare advocates plan to ask the judge to order an expeditious transfer of the APF chimps to the sanctuary.