YELLOWSTONE NATIONAL PARK, Wyo. (AP) — 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.

Buffalo Field Campaign and Western Watersheds Project argue that two separate groups of bison in the park are genetically distinct.

The Fish and Wildlife Service, citing a different study, says the herds are not genetically distinct.

The Billings Gazette reports a federal judge in Washington, D.C., has ruled that the federal agency failed to articulate why it chose one study over the other.

The Fish and Wildlife Service rejected the bison listing request in 2019.