New estimate of less than 50 Sumatran rhinos shows dangerous population drop

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  • The official population estimate for Sumatran rhinos has for years been pegged at “fewer than 80,” but a new estimate compiled by rhino experts from the IUCN and TRAFFIC concludes that the number is more likely between 34 and 47 rhinos left in the wild.
  • Another nine rhinos currently live in captive-breeding centers in Indonesia, where three calves have been born since 2012.
  • A survey by the same groups estimated the population at 73 animals in 2015, which indicates a population decline of 13% per year. Experts say the drop likely indicates both dwindling numbers and previous overestimates.

The world’s most endangered large mammal is in even worse shape than previously reported, according to a new population estimate.

For years, officials and experts have said there were “fewer than 80” Sumatran rhinos (Dicerorhinus sumatrensis) left in the wild. This figure has been used both by the Indonesian government and Sumatran Rhino Rescue, a consortium of NGOS, that have since 2018 worked on a plan to capture and breed more rhinos. However, the new estimate, compiled by wildlife trade watchdog TRAFFIC and the Asian Rhino Specialist Group at the IUCN, the global wildlife conservation authority, concludes that the real number of rhinos is just 34-47, down from their previous minimum estimate of 73 animals. in 2015.

The new estimate is based on interviews with on-the-ground rangers who have been attempting to count rhinos in four distinct locations using camera traps as well as other rhino signs such as footprints, wallows and distinct feeding patterns.

“We got these numbers from the field team leaders who had the best handle on what the actual numbers might be,” said Susie Ellis, co-author of the report and former head of the International Rhino Foundation (IRF).

Sumatran rhinos live in remote and dense tropical forests and highlands, making it incredibly difficult to get accurate numbers. They are the only animals in the genus Dicerorhinus, making them distinct from all other living rhinos. The smallest rhinos in the world, they are also known for their shaggy hair and their vocal dispositions: they whistle, squeak and grunt. Park officials have turned to camera trapping in recent years to gain a better understanding of the population, but even that has not put doubts to rest.

A Sumatran rhino
Sumatran rhinos live in remote and dense tropical forests and highlands, making it incredibly difficult to get accurate numbers. Image by Rhett A. Butler/Mongabay.

“These are unbelievably hard to find, track, monitor animals,” said Nina Fascione, the current head of the IRF, who was not involved in the study. “They’re reclusive. These are thick jungles. You could have a rhino 20 feet [6 meters] away and don’t know it.”

The report notes that the current population estimate represents a 13% decline every year from 2015-2021. While the population is definitely believed to be declining, the numbers also probably reflect an overestimate of rhinos from the past.

“In my opinion, the population has always been overestimated, beginning in 2008 or so,” Ellis said.

According to the new study, the wild population is split into four distinct areas. The researchers believe two to three wild rhinos still survive in Kalimantan, the Indonesian portion of the island of Borneo (in addition, one rhino is currently in captivity there); 12-14 in Way Kambas National Park in southern Sumatra (where an additional eight live at a captive-breeding center); and the largest population in Gunung Leuser National Park in northern Sumatra. Here, camera traps have recorded 18 individuals, but researchers think there may be 20-30 left.

The population estimate also states that rhinos might be hanging on in Bukit Barisan Selatan National Park, also in southern Sumatra. However, no rhino has been recorded in this park for years, and even camera traps have failed to capture any trace of them.

“It’s hard to believe there are any Sumatran rhinos left there,” Ellis said.

Still, some park authorities have argued that a few may persist. The recent estimate says that fewer than five might be in the park.

“It’s hard to prove a negative,” Fascione said. “We’re not seeing signs of rhinos, although I hear some mixed things. There are enough people on the ground who indicate that there may still be a few rhinos that I suppose it can’t be ruled out entirely.”

She added that the IRF is willing to pay for analyzing any suspected stool samples from the park, if any are brought in. Experts can often confuse tapir and rhino stools, just as they can confuse the footprints of both large mammals.

If any rhinos survive here or in Kalimantan, the population isn’t large enough to sustain itself even in the short term.

The Sumatran rhino, like all other rhinos, has suffered from thousands of years of human hunting. In the modern age, the demand for rhino horn — for various health benefits that have never been medically proven — has pushed every rhino species towards extinction.

Although rangers have found no evidence of Sumatran rhinos being poached in recent years, Ellis said she “believes[s] poaching continues,” adding that “there needs to be much more aggressive government intervention, and corruption among local authorities needs to be addressed.”

Today, however, Sumatran rhinos may be more imperiled by the simple fact that there are so few left that they rarely meet and successfully breed. Female Sumatran rhinos commonly suffer from reproductive problems, making reproduction both in the wild and captivity even more challenging. Like many megafauna, Sumatran rhinos are also incredibly slow breeders, with a 15-month gestation period and a minimum of three to four years between calves.

A Sumatran rhino calf.
A Sumatran rhino calf, one of eight Sumatran rhinos currently living in captivity. A new estimate pegs the remaining wild population at 34-47 individuals. Image by Rhett A. Butler/Mongabay.

The long decline of the species led conservationists to enact a captive-breeding effort in the 1980s that was rife with mistakes, but eventually produced calves beginning in the 2000s. The most recent was born in March this year, bringing the total number of captive rhinos up to nine, although breeding remains frustratingly slow.

The plan by Sumatran Rhino Rescue to capture more individuals from the wild to enhance the captive-breeding program (many of the individuals in captivity today are directly related) was delayed due to the COVID-19 pandemic.

Requests for comment from Indonesia’s environment ministry were unanswered as of press time. However, Fascione said she believes Indonesian officials are aware the situation is “dire” and are working to respond.

“The government of Indonesia is doing a lot to move forward. They absolutely are. They are working on the emergency action plan. The national park directors are all incredibly behind this and working collaboratively,” Fascione said, adding that she believes rhino captures will begin in earnest next year.

“This is the Hail Mary pass, this is it. I think that’s clear to everyone… There used to be more intellectual disagreements among them [conservationists about] the best way forward. The good news is, everybody’s on the same page right now.”

Banner image: Sumatran rhinos are the smallest rhinos in the world. Image by Rhett A. Butler/Mongabay.

Animals, Conservation, Critically Endangered Species, Endangered, Endangered Species, Environment, Extinction, Mammals, Rhinos, Sumatran Rhino, Wildlife, Wildlife Conservation

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