From beavers in the UK to bison in Romania and jaguars in Argentina, ecologists around the world are reintroducing animals that once flourished in particular areas. The theory is, if done correctly, they can boost biodiversity and restore ecosystems with benefits ranging from reducing forest fires to tackling invasive species. But the strategy is controversial. Opponents say some species are no longer suited to certain areas and cause conflict with farmers, adding there is little evidence it works. Proponents admit some well-meaning projects haven’t worked in the past, but insist properly planned rewilding, which has involved all the stakeholders from the start, can be very successful. We take a close look.

Presenter: Myra AnubiReporter/producer: Claire BatesSeries producer: Jon BithreyEditor: Penny MurphySound mix: Gareth Jones