Northern white rhinos are now on the verge of extinction after one died in a reserve in Kenya this weekend.
The rhino, called Suni, "was probably the last male capable of breeding", according to Discovery News, citing Dvur Kralove zoo in the Czech Republic, where the rhino was born back in 1980.
There now only six of the rare rhinos left, after most of them were hunted by poachers in east and central Africa for their horns, which are highly sought after for traditional Chinese medicine.
The Czech zoo is one of the only in the world to successfully breed the species in captivity, according to Discovery News.
Suni, who died from natural causes in the Ol Pejeta reserve, was one of two males and two females from Dvur Kralove zoo reintroduced into the wild in Kenya in 2009, in an operation called "the last chance of survival."
Experts hoped that the females' hormones would normalize in the wild.
"One can always believe in miracles but everything leads us to believe that hope they would reproduce naturally has gone," the zoo's spokeswoman Jana Mysliveckova said to AFP.
Sperm from the males born at Dvur Kralove has been conserved at the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, according to Discovery News.
Another pair of the rhinos live at the Wild Animal Park in San Diego in the United States, but they are too old to reproduce. Another aged female remaining at Dvur Kralove, close to the border with Poland.
"The number of rhinos killed by poachers has increased incredibly in the past few years," Mysliveckova said. "According to some scenarios, there will be no rhinos left in the wild in Africa in 10 years or so."
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