It's not an easy time to be a conservationist. Between the climate crisis, single-use plastics and mass deforestation, the world's wildlife is under constant threat from what some scientists are calling a 'mass extinction event'. But an increasing number of programmes are attempting to shore up threatened species by reintroducing animals to places they once lived. These are the best-known and best-loved animals to have been reintroduced to their former habitats...