Robin Hanbury-Tenison, the 90-year-old founder of Survival International, is cycling 104 miles down the River Thames on a water-bike to raise funds for a research station studying Britain’s temperate rainforest. Supported by his son, Merlin, he will begin the journey from Oxford on Friday, aiming to reach Richmond by Monday. The challenge comes as Hanbury-Tenison shifts his focus to protecting the overlooked rainforest fragments near his home in Cornwall.