Six critically endangered black rhinos are being transported from South Africa to Chad, restoring the species to the country in north-central Africa nearly half a century after it was wiped out there.

African Parks, a Johannesburg-based conservation group, said Thursday that the rhinos will travel by air to Zakouma National Park, a reserve in Chad that it manages with the government.

The group says the goal is to help the long-term survival of black rhinos and to restore biodiversity in Chad. It says there are fewer than 25,000 rhinos in the African wild, of which about 20 percent are black rhinos and the rest white rhinos.

Most of the rhinos are in South Africa, though the population has been hard hit by poachers supplying horns to an illegal Asian market.