In the spectacular Yellowstone where wolves, bears, coyotes, bison and elk roam vast grasslands, wetlands and forests, Steve Backshall looks for the answer to a puzzle. Wolves and beavers have little to do with each other so why, when wolves were returned after an absence of 70 years, did the beaver population increase? The revelation is as magical as it is surprising. A BBC Production.

Originally released by BBC Worldwide Learning, 2012. Streaming video file encoded with permission for digital streaming by Infobase on October 03, 2015.