Isabel Esterman, Mongabay | March 3, 2021
Conservationists trying to save the Sumatran rhino from extinction face a critical dilemma: In seeking to build a robust captive-breeding program, should the healthiest, most fertile rhinos be left in the wild or brought into captivity?
It’s a question with no simple answers.
The species, Dicerorhinus sumatrensis, once roamed from the Himalayan foothills to the islands of Borneo and Sumatra, but is today only known to survive in a few small pockets of forest in Indonesia. No more than 80 individuals are believed to be left on Earth.
Decades of poaching and habitat loss brought the species to this point. But today, most experts believe that protecting the few remaining wild rhinos in situ is not enough to sustain the species.
Because the remaining wild rhino populations are so small and so isolated from one another, the rate of births in the wild is likely no longer enough to offset even natural deaths.
In 2018, a coalition called Sumatran Rhino Rescue, which includes the Indonesian government as well as local and international experts and conservation groups, announced the launch of a new and more intensive captive-breeding program. There are currently eight rhinos in conservation breeding facilities: seven at the Sumatran Rhino Sanctuary in Way Kambas National Park in southern Sumatra, and one at a facility in Indonesian Borneo. The coalition aims to boost numbers at the existing facilities, as well as establish additional centers in Indonesia, starting with one in the Leuser ecosystem at the northern tip of Sumatra.
However, while a broad consensus has been reached about the need for human intervention to boost Sumatran rhino numbers, there is less agreement about which rhinos to capture.
Since 1994, captures of Sumatran rhinos have been very limited, and have focused on so-called “doomed animals” that were known to be isolated from other rhinos, that appeared to be injured, or whose habitats were precariously close to human settlements or areas being cleared for timber or agriculture.
Rhinos that were living in protected areas, and that were reasonably likely to encounter and breed with each other, were left in place.
This strategy was meant to minimize disruption to wild populations. But it came with some major downsides.
Scientists are learning more about the Sumatran rhino’s biology, and reproductive physiology, all the time. One key discovery, made in the late 1990s at Cincinnati Zoo, is that females are induced ovulators, meaning they need external stimulus — most likely the presence of males — to kick-start their reproductive systems. Further, females that do not ovulate and mate are particularly prone to developing tumors and other reproductive pathologies that can leave them infertile.
This, along with age and other health issues, means that the “doomed rhinos” may be unable to reproduce, and that investing time and resources into capturing such rhinos for breeding might be futile.
Rhinos from the few small populations that are still breeding in the wild are more likely to be fertile. However, such rhinos are also, of course, more likely to give birth in the wild than their “doomed” counterparts. And removing too many healthy animals from these tiny wild populations could jeopardize the species’ odds of surviving in the wild.
On top of that, experts have to account for the risk inherent in capturing rhinos from the wild. The potential downsides are epitomized in the case of Najaq, a female rhino who was captured in Borneo in 2016, but died within a month.
Likewise, when Mongabay contributor Jeremy Hance analyzed records of Sumatran rhinos captured during a previous initiative to capture rhinos for breeding, which ran from roughly 1984-1995, he found that at least three rhinos died at the capture site and at another five did not survive more than a year of captivity.
Furthermore, out of at least 46 rhinos that have been captured since 1984, only two pairs have produced offspring: a male and female captured in Sumatra and transferred to Cincinnati Zoo in the U.S. produced three calves. One of those calves was later transferred to the Way Kambas sanctuary, where he has since fathered two calves from a wild-caught female. (Malaysia’s Malacca Zoo also had one birth in 1987, from a female who was pregnant at the time of her capture.)
In some respects, this history of births is hopeful. Many of the key challenges and mysteries of Sumatran rhino reproduction were finally solved by the beginning of the 21st century. From 1984-2001, no Sumatran rhinos were successfully bred in captivity; indeed, no captive-bred births had been recorded since 1889. But building on insights from the three births achieved at Cincinnati Zoo — in 2001, 2004 and 2007 — the Way Kambas sanctuary has seen births in 2012 and 2016.
No Sumatran rhinos have been born in captivity since, however. And only one living captive male and one living captive female have proved capable of producing viable offspring.
As a result, some experts argue that as many rhinos as possible should be captured as quickly as is feasible. This, they argue, gives us the greatest chance of boosting the population before it simply dwindles into extinction. Others call for a more measured path, citing the potential benefits of simply protecting viable rhino groups in the wild and allowing them a chance to breed on their own.
The COVID-19 pandemic put the brakes on plans to capture more rhinos, but as and when restrictions lift, conservationists will once again have to grapple with this fundamental dilemma about the future of the breeding program, and the species as a whole.