The Sumatran rhinoceros is one of the most endangered animals on Earth, having lost more than half of its wild population in the last 10 years alone. When scientists revealed at a recent "Sumatran Rhino Crisis Summit" that only about 100 individuals still exist in the wild, it became clear drastic measures are needed to save the species from extinction.

How drastic? Two Sumatran rhino siblings at the Cincinnati Zoo will be paired as mates, zoo officials announced Sunday, part of a last-ditch scramble for new offspring.

"Harapan," a male born at the Cincinnati Zoo in 2007, was shipped back this month after spending the last few years at a Florida conservation center and the Los Angeles Zoo. The plan is to mate him with his 9-year-old sister "Suci," the only other Sumatran rhino in North America. Inbreeding is bad for genetic diversity, but experts say the rhinos' tiny wild population means it's likely already happening in nature. Their goal is to have enough captive animals, especially young ones, to stop the species from dying out.

"No one wants to breed siblings," says Terri Roth, vice president of conservation and science at the Cincinnati Zoo, in a statement about the plan. "[B]ut when a species drops below 100 individuals, producing more offspring as quickly as possible trumps concerns about genetic diversity. We are down to the last male and female Sumatran rhino on the continent, and I am not willing to sit idle and watch the last of a species go extinct."

The Cincinnati Zoo has been a beacon of hope for the species since 2001, when it produced "Andalas," the first captive-born Sumatran rhino in 112 years. Along with his mate, "Emi," he sired both Suci and Harapan before he was shipped to Indonesia in 2007 to join a breeding program there. Following Emi's death in 2009, the siblings now represent North America's entire population of Sumatran rhinos.

Although Indonesia also has a captive breeding program, experts in the U.S. say it's limited by a reluctance to capture wild rhinos for desperately needed fresh genes, and to exchange its rhinos with other breeding programs to avoid inbreeding.

"The captive breeding program in the U.S. has been the most significant contributor to the survival of the Sumatran rhino in recent years, and in particular the progress that the Cincinnati Zoo has made in determining the reproductive strategy of this species," says Los Angeles Zoo mammal curator Jeff Holland. "This is one reason why it is vitally important to maintain a captive population of Sumatran rhinos in the U.S., and secondly to avoid having all the rhinos in one place where they are at risk of disease, poaching or natural disaster that could potentially wipe out the entire captive population in a single stroke. The idea of two captive populations lessens the risk of something like this happening."

And while it may seem odd to breed siblings as a way of preserving a species' genetic diversity, Roth points out it sometimes happens in the wild, especially when populations are small and unconnected. And unlike wild inbreeding, which can plague a gene pool for generations, the zoo's efforts will be carefully managed and informed by science.

"We know it happens in the wild, and with a population like the Sumatran rhino that's so small and fragmented, it's probably happening in the forests of Sumatra right now," Roth says. "And if you inbreed [just] one generation, as soon as you outbreed that particular offspring, the inbreeding disappears. So you can correct it pretty quickly."

Check out the video below for more on the zoo's plan to save Sumatran rhinos:

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To save species, zoo may mate rhino siblings
As the endangered Sumatran rhinoceros teeters near extinction, scientists are racing to maintain a premier captive breeding population at the Cincinnati Zoo.