More evidence: Vocalizations

To add to the findings of the genetics and morphology work, Nowak had pushed University of Southern California graduate student James Askew to expand his research on vocalizations to include the orangutans from the Batang Toru forest of Tapanuli.

“Vocalizations are very flexible,” Askew says. Many factors, like environment, cultural innovations and genetics, can contribute to variations, which is why, he says, “you’d never go for a species definition on vocalizations alone.”

But finding a new species was not his interest. Askew had studied orangutan vocalizations since 2011 and wanted to know how they might differ between geographically distinct groups.

To ensure that any variations he uncovered were not simply cultural, he decided to focus on a vocalization that would be universal to all orangutans. So he chose the long call.

The long call is a series of barking bellows made by sexually mature male orangutans. It’s used to attract females, deter other males, and also give information about both the caller and what’s going on in the area. The call reverberates through the forest and can be heard from great distances, often more than one kilometer (0.6 miles) away. It also lasts for a long time, somewhere between 1 and 10 minutes.

“The long call is a social cue to call a mate, like a bird song,” says Gabriella Fredriksson, SOCP’s Tapanuli program coordinator. “If the calls are so different, a species won’t recognize each other’s call, and the female won’t react. So in some species, if the call has become so different, it can indicate speciation.”

Researcher James Askew in the field collecting orangutan vocalizations. Image courtesy of James Askew.

Initially, Askew alternated between three study sites: one in Central Kalimantan province, another in East Kalimantan (both in Borneo), and a third in Sumatra’s Leuser ecosystem. In 2015, forest fires made it impossible for Askew to return to his Central Kalimantan study site. With Batang Toru on his radar due to discussions with Nowak, Askew decided to expand his research on vocalizations to include the Batang Toru orangutans.

Typically, Askew and his team would set out at dawn to find and record the orangutans.

“We would listen for the sound of an orangutan chomping on fruit or bark, or the swishing sound of orangutan moving through trees. But we had to move slowly because if they heard you coming, they’d hide or move away. And then we probably couldn’t catch up,” he says.

The rugged terrain of Batang Toru made the research even more difficult, he says. “We’d trek up and down steep hills, and sometimes lose animals when they went down into a ravine.”

Over the course of four years in all the locations, Askew taped more than 200 hours of long calls. And when he compared their acoustic characteristics, he found three distinct calls.

Sumatran orangutans had calls that were prolonged and low-pitched. Bornean orangutans belted out calls that were shorter in duration but higher in pitch. In contrast, the calls of Batang Toru males were mixed: long like Sumatran orangutans but high-pitched like the Bornean apes.

“It was a nice additional piece of information,” Askew says, and it confirmed what the others had found: a new species.

The trifecta

While the genetics research suggested the Tapanuli orangutans were distinct, it wasn’t until a skeleton became available (from a male orangutan named Raya who was shot by residents in 2013 and died in the care of the SOCP eight days later) and showed significant morphological differences that the scientists considered proposing it as a new species.

“That was the smoking gun we were waiting for,” Krützen says. “Describing a new species is like going to court, with no predetermined list of what’s needed.” But taking the genetic, morphological and vocal evidence together, “this was the gold standard.”

On Nov. 2, 2017, the entire team announced their discovery in an article, titled “Morphometric, Behavioral and Genomic Evidence for a New Orangutan Species.” The 37 co-authors outlined the genetic, morphological and vocal evidence that justified their finding.

“It was a massive collaborative effort,” Krützen says.

The Batang Toru River, the proposed power source for a Chinese-funded hydroelectric dam. Image by Ayat S. Karokaro/Mongabay-Indonesia.

Threats to this already critically endangered ape

From the moment news broke about the Tapanuli orangutan, it was under threat.

Of most immediate concern is a planned 510-megawatt hydroelectric dam by the Indonesian firm PT North Sumatra Hydro Energy (NSHE). This $1.6 billion project, financed by the Bank of China and built by the Chinese state-owned company Sinohydro, will occupy about 650 hectares (2.5 square miles) of land along the Batang Toru River in South Tapanuli district. The project involves a reservoir, spillway, quarry, camp, road access and other facilities, such as tunnels, power station and transmission lines.

Conservationists say infrastructure like roads and tunnels will cut through rugged primary forest that contains the highest population densities of Tapanuli orangutans.

“This is one of the last remaining bits of lower elevation landscape left,” says Nowak. “There is a reason why orangutan densities are high in this area.

“Usually as you go up in elevation, preferred orangutan food resources start to dwindle and populations can’t be maintained at high densities. As such, orangutans prefer low elevations,” he says. “Most of the Batang Toru ecosystem is at more than 800 meters [2,625 feet] above sea level (i.e. submontane forest). While the species is able to exist in these areas, having the ability to move between upland and lowland areas is critical for a healthy orangutan population.”

NSHE spokesman Firman Taufick disputes concerns about the impact of the project on the orangutans. “The project area is not the primary habitat of orangutan,” he says, citing studies carried out in 2017 and 2018 by the Aek Nauli environmental research center and the North Sumatra provincial administration’s conservation agency.

Taufick also says the tunnel carrying water from the turbine back to the river is designed to be 50 to 200 meters (165 to 655 feet) underground. “Therefore,” he says, “there is no land clearing above the tunnel to avoid the habitat fragmentation.” He also says the inspection road is built parallel to the Batang Toru River, which is already a natural divide between the western and eastern habitats. “This design is made to avoid new fragmentation,” he says. “Therefore, there is neither tunnel nor inspection road that cleaves the primary forest.” He also says the road provides only “limited access directly to the project site” and that the company has adopted “a zero-tolerance policy” toward illegal logging and the ownership and hunting of animals.

Taufick says NSHE has adopted the International Finance Corporation’s (IFC) standards for biodiversity.

Even before scientists confirmed the existence of a new ape species in the forests of Batang Toru, local people protested against the planned dam. Picture in August 2017, dozens of indigenous people in North Sumatra protest against the development, saying it threatens to take over the lands they hold sacred. Photo by Ayat S. Karokaro/Mongabay-Indonesia.

However, the IFC standards leave considerable room for flexibility. They state that impacts on biodiversity and ecosystem services should be avoided, but that when that is not possible, mitigation measures should be put in place. The standards also make allowances for mitigation that doesn’t work, suggesting that measures should change in response to changing conditions and monitoring.

Many scientists and conservationists suggest these measures are inadequate to address the significant negative and permanent impact of this project on the orangutan’s habitat.

In June 2018, a team from James Cook University and the University of Indonesia published a study in Current Biology that estimated that the impact of the hydropower project would stretch far beyond its reservoir and alter about 8 percent of the Tapanuli orangutan’s remaining range.

Ian Singleton, director of the Sumatran Orangutan Conservation Programme, says that while the developers claim the dam is small, “the infrastructure is massive and it will have an irreversible impact on these orangutans.”

He says the construction will further open the forest and increase opportunities for people to settle in the area, clear more land, and hunt. That, in turn, will increase the likelihood of conflicts between people and orangutans — a situation, he says, that rarely ends well for the orangutans, like Raya.

Fredriksson, the SOCP’s Tapanuli coordinator, agrees that the consequences are serious. There are so few Tapanuli orangutans that “this species can’t afford even an offtake of a few individuals.”

Orangutans breed very slowly. Sumatran orangutans have the longest interval between births of any mammal. Females give birth for the first time when they’re about 15 years old and then reproduce again only every eight to nine years. Given their 50- to 60-year life span, that means they will have just four to five infants in their lifetime.

Even more problematic, conservationists say, is that the hydropower development threatens to further fragment the already dissected forests where the Tapanuli orangutans live. The species is split into three subpopulations: one of less than 600, another of about 150, and a third of several dozen. In chopping up their already limited habitat, it will impede the orangutans’ ability to move between various forest blocks and also permanently sever their ability to interact. Conservationists fear that will doom the smaller two groups, as they would not be able to maintain safe levels of genetic diversity. To be sustainable over the long term, scientists suggest 500 or more individuals are needed in a population.

“If we can’t connect the two smaller groups to the larger one, they will disappear,” Singleton says. “They’re just not big enough.”

In August 2018, the Indonesian Forum for the Environment (Walhi) filed a legal challenge to the hydropower project, arguing that the environmental permit from the North Sumatra government should have considered its potential impacts on wildlife and more (including impacts on the river, downstream communities, and the serious risk of damage from earthquakes, given that the dam is slated to be built on the Sumatran rift valley). A verdict in the case is expected March 4.

However, reports suggest that, as of early May 2018, 50 hectares (124 acres) have already been cleared in preparation for project’s construction.

“It’s already started,” Singleton confirmed. “They have built a road up the river and cleared areas to dump the waste [from the tunnel].”

With only 800 Tapanuli orangutans remaining in the wild, there is little room for error — and efforts need to be made to ensure their existence, not hasten their demise.

Banner image: a juvenile Tapanuli orangutan, by Andrew Walmsley.

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