Some of the last few northern white rhinos still alive are being moved from their home in central Africa amid fears that poachers will wipe them out.
There could be more northern whites in zoos than in the wild
Five of the animals are to be flown from the Democratic Republic of Congo to Kenya in the next month.
Fewer than 10 of them are believed to remain in the wild.
A spokeswoman for DR Congo's Garamba national park says the government has approved relocation after poaching outstripped local conservation efforts.
According to the International Rhino Foundation heavily armed poachers on horseback launch raids into the national park from neighbouring Sudan.
Rhino horns fetch high prices in some cultures for their supposed medical properties.
Most endangered mammal
Northern white rhinos once roamed in large numbers throughout north-central Africa south of the Sahara.
The population has been virtually destroyed since the 1970s, when there were thought to be about 500 northern whites.
Conservation efforts were having some success in rebuilding the population until recently, when nearby civil wars and an increase in poaching sent their numbers plummeting again.
Nine of the rhinos, including a pregnant female and a young calf, were found dead in 2004.
The decline means the rhino is thought to be the most endangered large mammal on earth.
There are 10 in zoos in the Czech Republic and the US, but only one calf has been born in captivity in the last decade.
"Although we've all been against the idea of the rhinos going elsewhere it is now necessary," said Kes Hillman Smith, head of monitoring at Garamba.
"Although huge efforts are being put into conservation, it is not working fast enough," she told Reuters news agency.
"The poachers are still winning and there are not enough rhinos to last out at this rate."