On assignment for BBC Future Planet.
Thousands of years ago, the wild ancestors of cattle and horses roamed freely across the Côa region, Portugal, migrating in large herds and playing a key role in maintaining grassland ecosystems.
Now, Rewilding Portugal is bringing back large grazers such as Sorraia horses and tauros, a specially bred version of the long-extinct auroch cattle with a mission to create a 1,200 sq km wildlife corridor along the Côa River, improving habitat connectivity between the Douro River in the north and the Malcata mountains in the south.