BILLINGS, Mont. (AP) — A federal judge has ordered U.S. wildlife officials to reconsider a 2015 decision that blocked Endangered Species Act protections for iconic bison herds in Yellowstone National Park. U.S. District Judge Christopher Cooper said in a ruling late Wednesday that the U.S. Fish and Wildlife Service failed to consider a scientific study suggesting the park's bison population might be too small to sustain its two herds. Yellowstone's 5,000 bison make up the largest remaining wild population of a species that once numbered in the tens of millions. The animals, also called buffalo, are routinely slaughtered by state and federal agencies during their winter migrations outside the park. Wildlife advocates from the Buffalo Field Campaign and other groups sought protections for the herds in 2014, then sued when their petition to the government was denied.