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New calf brings new hope, and new concerns, for embattled Sumatran rhinos

Male rhino calf born Nov. 25, 2023. Image courtesy of the Indonesian Ministry of Environment and Forestry.

  • A male Sumatran rhino calf was born Nov. 25 at Indonesia’s Sumatran Rhino Sanctuary in Way Kambas National Park, marking the second birth at the facility in as many months.
  • Independent estimates put the species’ wild population at no more than 47 individuals, so each new birth increases hopes the species can be saved from extinction; the new calf brings the captive population up to 11.
  • However, the birth also highlights weaknesses of the captive-breeding program: the father and mother of the new calf are related, a consequence of all the male rhinos currently in captivity being descended from a single genetic line.

The Sumatran rhino became a little safer from extinction over the Thanksgiving weekend. On Nov. 25, at around 4 a.m. local time, first-time mother Delilah gave birth to a healthy baby male Sumatran rhino (Dicerorhinus sumatrensis) at the Sumatran Rhino Sanctuary (SRS) in Way Kambas National Park on the Indonesian island of Sumatra. The baby came about 10 days before full term — Sumatran rhino gestation lasts around 16 months — but the government says the calf is healthy, weighing in at 25 kilograms (55 pounds). It’s also the first offspring for father Harapan.

The birth is extra special, because it’s the first time a female rhino born in captivity — Delilah was born in 2016 at the SRS — has given birth herself. (Harapan was born at Cincinnati Zoo in 2007.) The birth is also the second at the SRS in less than two months: on Sept. 30, a female calf was born. With this, the birth further cements the SRS’s run of successes for what is potentially the most endangered large land mammal on the planet.

“The Sumatran rhino breeding program has never been in a better position,” Nina Fascione, the International Rhino Foundation’s (IRF) executive director, said in a press release. “Two years ago, there was only one captive Sumatran rhino pair in the world able to successfully produce offspring. Now there are three pairs — six rhinos — who are proven breeders. Those are much better odds for the long-term survival of this species.”

A male rhino calf, which still remains unnamed, was born Nov. 25, 2023 at the Sumatran Rhino Sanctuary in Indonesia’s Way Kambas National Park. The second calf born at the center in as many months, it exhibits the furry coat and large eyes typical of its species. Image courtesy of the Indonesian Ministry of Environment and Forestry.

Indonesia’s minister of environment and forestry, Siti Nurbaya, said in a press release that she was “grateful” for the new birth, the fifth at the facility.

Still, the critically endangered rhino exists on a razor’s edge. With the new birth, there are now 11 Sumatran rhinos in captivity. In the wild, the species is almost gone. Officially, the government says there are fewer than 80 Sumatran rhinos left in the wild. But last year, an independent estimate put the number at just 34-47 wild rhinos. Sources have said for years that the population is plummeting and that there may only be one rhino population left that might be self-sustaining in the short-term: a remote population in Gunung Leuser National Park at the northern tip of Sumatra.

In 2018, after decades of debating, Indonesia announced it would start capturing rhinos from the wild to supplement its small, but successful, captive-breeding population. But five years on, it has only caught one animal: Pahu, a female from the island of Borneo, who has still not been used in the breeding program. Sources say Pahu is too small and old for natural breeding, but this year researchers reported that they successfully extracted eggs from Pahu, which may be used to produce an embryo that can then be implanted into a surrogate at the Way Kambas SRS to bring to term. Pahu’s genetics are especially valuable as she comes from a different subspecies from the animals at Way Kambas.

The need for new animals in the captive-breeding program is highlighted by the most recent birth. The male calf’s parents, Delilah and Harapan, are related; Harapan is Delilah’s uncle on her father’s side. Currently, all the males in captivity are related, descended from a single male, Ipuh, who lived at Cincinnati Zoo.

The newborn calf’s mother, Delilah, was born at the sanctuary in 2016. The calf’s father Harapan, is Delilah’s uncle, highlighting the limited genetic diversity in the captive population. Image courtesy of the Indonesian Ministry of Environment and Forestry.
Officials say the calf is healthy, weighing in at 25 kilograms (55 pounds). Image courtesy of the Indonesian Ministry of Environment and Forestry.

“This is an emergency situation. There is no choice,” Fascione told Mongabay of the need to pair up related animals. “This is just the only option for the population that we have.”

She adds that in the near term, some degree of inbreeding isn’t extremely risky for an animal like this.

“The good news is there are longer-terms plans for capturing an animal up in Leuser … And getting some fresh genes in the population,” she said. “All it would take is a couple of new individuals, bringing new genes.”

This is one reason why there’s been rising pressure on the Indonesian government to capture additional rhinos from the wild.

The smallest rhino in the world, the Sumatran rhino is also the oldest on the evolutionary tree, likely splitting off from the other existing rhinos around 15 million years ago. It’s an evolutionary marvel, the last species from the genus Dicerorhinus. The Sumatran rhino is related to the now-extinct woolly rhino, and remains the hairiest of the living rhino species. It’s also known as the most vocal of all rhinos: they “sing,” making sounds that have been compared to those made by dolphins. They also snort and grunt, and those at Way Kambas have been known to become quite attached to the keepers who care for them.

In the Indonesian environment ministry’s press release, conservation chief Satyawan Pudyatmoko noted that Sumatran rhinos born in captivity could be eventually be used to supplement the wild population. This would involve releasing them back into the wild where Sumatran rhinos still exist, presumably Gunung Leuser National Park.

“That is the definitely a long-term goal,” Fascione told Mongabay. “Save and rebuild the population while protecting forest lands and ultimately reintroductions into the wild. We are a long way from that.”

Animals at the Sumatran Rhino Sanctuary are cared for in forested enclosures in their natural habitat. Using captive-born rhinos to supplement wild populations is a long-term goal of the breeding program, but one experts say is a long time off.  Image courtesy of the Indonesian Ministry of Environment and Forestry.

So, for the moment, the attention turns back to first-time mom Delilah and the new male calf, so far unnamed.

“You never know if a first-time mom will know what to do, but Delilah brought that calf into the world and started nursing it with no fuss or fanfare,” Fascione said. “It’s an incredible event that gives hope to the future of this critically endangered species.”

Banner image: The newborn rhino calf at the Sumatran Rhino Sanctuary in Way Kambas, Indonesia. Image courtesy of the Indonesian Ministry of Environment and Forestry. 

Sumatran rhino birth is rare good news for species sliding to extinction

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