Black rhinos are being reintroduced into a billionaire-backed national park in Zimbabwe’s Zambezi Valley three decades after almost all of them were evacuated to protect them from poachers.

The number of black rhinos in the valley fell to 400 in the early 1990s from about 3,500 a decade prior because of a surge in illegal hunters crossing from Zambia who targeted the critically endangered species for their horns. The animals that survived were moved to safer areas in Zimbabwe, Texas and Australia.