In the Yungas region in Bolivia, jungle and steep cliffs, people do not walk - they fly. These bird men are known as 'cocaleros', coca harvesters.They use ropes to swing across the narrow valleys, suspended from ancient rusting pulleys. It takes just 30 seconds from one side to the other. By foot it would have taken more than an hour.It is almost a form of public transport, there are about twenty cables strung across the valley. All day long, people and goods fly across the river 200 meters below.