Do mountain bison roam Yellowstone?

From the Jackson Hole News:

Bob Jackson — a bison behavior expert, outspoken critic of the National Park Service and former Yellowstone ranger — says mountain bison lived on the high-elevation plateau south of Lamar Valley for thousands of years before the plains bison were reintroduced to the park. Though the two subspecies have likely interbred, he said, the mountain bison likely retained much of their genetic heritage and their “culture,” which has enabled them to survive for thousands of years without leaving the park.

or maybe not:

But according to Yellowstone spokesman Al Nash, recent reviews of scientific literature, conducted in conjunction with work on the park’s winter-use plan, suggest that Yellowstone bison have always ranged outside the park in the winter.

“There was a time when scientists thought there might be two subspecies, the mountain bison and the plains bison,” Nash said. “But most scientists really don’t see that distinction any more.”