YELLOWSTONE NATIONAL PARK, Wyo. >> A federal judge has ordered the U.S. Fish and Wildlife Service to revisit part of its decision not to protect Yellowstone National Park’s bison as an endangered species.

The Buffalo Field Campaign and Western Watersheds Project groups have been fighting since 2014 to have Yellowstone’s bison declared endangered or threatened under the Endangered Species Act.

They have argued that two separate groups of bison in the park are genetically distinct. Rather than set a population limit of 3,000 animals for the entire park, they said, the limit should be 3,000 for each herd, or 6,000 overall.

The Fish and Wildlife Service, citing a different study, has argued that the herds are not genetically distinct and rejected the listing petition in 2019, the Billings Gazette reported.

The federal agency failed to articulate why it chose one study over the other, District of Columbia U.S. District Judge Randolph D. Moss wrote in an opinion last week.

Moss set no deadline for the Fish and Wildlife Service to respond but will require both sides to update the court on the case within 90 days.