From this story in the New York Times:
Seven decades after the last reported sighting of the eastern cougar, the federal Fish and Wildlife Service declared it extinct Wednesday and recommended that it be removed from the nation's endangered species list. There's one wrinkle, though: it may not be extinct, exactly. Scientists are moving toward the conclusion that the eastern cougar was erroneously classified as a separate subspecies in the first place. As a result of a genetic study conducted in 2000, most biologists now believe there is no real difference between the western and eastern branches of the cougar family.
_Either way, the "eastern" cougar as such is no longer with us. Any recent sightings in the cougar's historic range, which stretched from eastern Ontario and Michigan eastward to Maine and southward to Georgia, Tennessee and Missouri, were actually sightings of its relatives, the Fish and Wildlife Service said. "It's extinct," said Mark McCollough, a wildlife biologist with the agency's offices in Maine, referring to the official determination by his agency. "But it's not?" he was asked. "But it's not," he confirmed. "It may well return to part of its range." Cougar populations from the West are following the eastward migration of the coyote, Dr. McCollough said, and some have settled in the Dakotas. At least one breeding pair is now in Nebraska, he added.