The news that both Elie and Madiba conceived after "natural" relations with the zoo's male rhino Jobi, came after a calf was born in San Diego zoo on Sunday.

Pairi Daiza zoo spokeswoman Claire Gilissen said the news was "fantastic" for all the team who are doing their "bit for the protection of this species."

There are around 18,000 southern white rhinos in the wild but the subspecies is being exterminated by poachers at a rate of one every eight hours.

Another species of rhino, the world's second-largest land mammal, the northern white, is in even more critical danger, with only two left in existence.

The remaining northern white pair are both female, so they will die out unless their genes can be preserved or recovered and an artificial breeding programme begins.

On Sunday, a southern white calf was born through artificial insemination in San Diego, in what the zoo hailed as a step toward perfecting the technique.

The Belgian mums-to-be are not breaking new scientific ground, but the zoo is delighted to have two births to look forward to by the end of the year.

Elie has already had a calf, Sethemba, who was born in 2016 and has been transferred to a zoo in the Spanish city of Malaga as part of Europe's captive breeding program.