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, which even hum when they are content.

In this clip, Prof Rogers approaches a mother bear protecting her cubs in a den.

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