For 43 years Professor Lynn Rogers has studied wild bears, walking with them, gaining amazing insights into their behaviour.

Far from being dangerous creatures, his studies reveal the bears as peaceful, playful creatures that even groom each other.

In this clip, Prof Rogers watches as suckling bears "hum", a unique sound bears produce when content.

Natural World: 'Bearwalker of the Northwoods', Wednesday 28 October, 2000GMT, BBC Two