Najin and Fatu are the last two northern white rhinos on the planet and they are both female and cannot carry pregnancies.
Scientists around the world are now in a race against time to save the species at the Ol Pejeta Conservancy in Laikipia in Kenya.
"Having the last two northern white rhino is a clear symbol of what extinction means and because these animals are not able to speak for themselves, we act as their voice," said Zacharia Mutai, Northern White rhino keeper, at Ol Pejeta.
How to save a species
The plan is to use eggs harvested by the two females and sperm collected from male northern whites saved before they died.
The embryos will be fertilised artificially and then implanted into a surrogate southern white rhino.
Last year, three embryos were successfully created, despite the coronavirus pandemic causing delays.
But for the moment implant embryos are still being tested in Europe.
It's an international effort, led by the Leibniz Institute for Zoo and Wildlife Research in Berlin, Germany, Avantea biotechnology research and animal reproduction lab in Cremona, Italy, Dvur Kralove Zoo in the Czech Republic, and the Ol Pejeta Conservancy and the Kenya Wildlife Service.
The procedure to create viable embryos has proven to be safe and can be performed regularly before the two females become too old.
Because those eggs are limited, scientists are practicing with embryos from southern white rhinos until they can establish a successful pregnancy.
'Running out of time'
"In terms of getting the eggs implanted back into the surrogate southern white rhinos to create northern white rhino pregnancies, we are still some way away from being able to do that," explains Richard Vigne, Managing Director, Ol Pejeta Conservancy.
For those involved in the effort, acutely aware of time, delays caused by the pandemic are all the more painful.
Already they are racing against time as Najin - now aged 32 - is getting old and her eggs may soon no longer be viable. Fatu was born in 2000.
"Time is not on our side. The two females are getting older by the day," said Vigne.
"In fact the oldest female Najin probably or may not be used for ovum pick ups in future because it seems as if her age has meant that the eggs are no longer viable.
"So we are running out of time. We need to continue, we are doing our best and we hope that one day we will be able to report a successful pregnancy and thereafter the birth of at least one, if not more, northern white rhino calfs," he said.
Decades of poaching have taken a heavy toll on rhinos as their tusks are used for carving material and prized in traditional Chinese medicine for their supposed healing properties.
But it is hoped technology and science can give the northern white rhino another shot at life