It was in 1997 when Li Jiahong, a 63-year-old wildlife protection expert, first heard the shrill calls of the Skywalker hoolock gibbon, one of the most endangered primates in the world.

Bursting from the canopies of the dense forest in the Gaoligong Mountains in southwestern China’s Yunnan province, the high-pitched and rhythmic sound “was like rolling down the hill, remote but very clear,” said Li, who then worked at the Longyang preservation office of the Gaoligong Mountains National Nature Reserve.

After that, Li started a rugged journey of tracking the animals, which were long known to locals as “black gibbons.” The gibbons’ arboreal nature makes them hard to follow and study. They spend most of their lives high in the trees, using their strong and flexible shoulders to swing through the canopy one arm at a time. Scientists often try to find them by following their songs, which can be heard from more than a mile away.

After an eight-year search from the high peaks to the deep valleys of the Gaoligong Mountains, Li in 2005 successfully took the first clear photo of the elusive creature — a female gibbon with dark gray fur and thin white eyebrows. Li named the gibbon Azhen.

In 2017, the black gibbon was formally identified as a new species of primate and was named Hoolock tianxing in Chinese, which is derived from the ancient Chinese classic “Book of Changes” and refers to the gibbons’ arboreal locomotion. The name, which translates into English as “skywalker,” also pays homage to the central family of characters in the “Star Wars” movie franchise, according to Fan Pengfei, a primatologist who named the species.

In 2018, the Skywalker hoolock gibbon was listed among the world's 25 most endangered primates. According to Fan’s studies, there are fewer than 150 Skywalkers living in China, mainly in the tropical rainforests of Yunnan. Their population is 10% lower than that of wild giant pandas. There are also a small number of clusters in Myanmar, but their situations are largely unknown.

The remaining Skywalkers in China live in separate clusters with impassable, human-made barriers between them. Many family groups and individuals are isolated, making it more difficult for them to interbreed and threatening the future of the species, experts said.

Scientists and preservationist are trying various methods using modern technologies to help isolated Skywalkers — which are usually monogamous and take years to breed offspring — to expand their living territory and find new partners. However, the clock is ticking for rescuing the Skywalkers from extinction, forcing scientists into a race against time.

Lonely inhabitants

The Gaoligong Mountains, at the southeastern extent of the Himalayas, are home to the world’s highest-elevation and highest-latitude tropical rainforests. With diverse geographic conditions and climates, the region is considered China’s biodiversity hot spot.

The unique songs of Skywalkers traveling around the dense rainforest are familiar to many locals, but only a few have had the chance to meet the creatures.

During years of photographing Skywalkers, Li closely followed Azhen’s family in the Nankang area, the southern part of the Gaoligong nature reserve. Azhen and her partner, Quiff, had a newborn when Li first found them.

The family had a neighbor — a single female Li named Partheno, or Lonely Girl. According to local villagers, Partheno lost her partner in the 1990s, probably because of poaching, as many local people believed gibbon brains to be a cure for epilepsy.

Since then, Partheno persistently tried to form a new family. She made numerous attempts to join Azhen’s family but was rejected. She cried every day in her unique, high-pitched voice in hopes of being heard by other gibbons, according to Li.

Skywalkers have a strong sense of family territory. A typical Skywalker family consists of two to five members including the parents and their offspring. Most adult Skywalkers are hesitant to move beyond their settlements. They use their shrill songs to search for mates and communicate with each other. But if their calls fail to get a response, they may spend their lives alone.

They “are like lonely people who make cautious attempts to move forward a little bit to seek whether there are any friends,” said Fei Hanlan, a scholar at China West Normal University in the southwestern Sichuan province. “If not, they will turn back to where they were.”

Like most Skywalker habitats in the Gaoligong Mountains, the Nankang area has become an island, isolated from other Skywalker habitats by highways, villages, and distance. Partheno and Azhen’s family were the only residents of the area.

The nearest habitat to theirs is more than 15 kilometers away, according to Fei. Studies found that Skywalkers usually migrate only within a 10-kilometer radius, meaning Partheno was very unlikely to meet other gibbons.

“Partheno is really pitiful,” Li said. “She cries days and nights (searching for a partner), while Azhen’s families mostly remains peaceful.”

Vanishing habitats

In 1917, American adventurer and naturalist Roy Andrews first found a Skywalker gibbon specimen in a forest in Gaoligong about 700 meters above sea level. The area has since been developed into farmland and villages.

The Gaoligong Mountains National Nature Reserve, founded in 1986, is one of the oldest nature reserves in China. But most of its zones are set in high-elevation areas, leaving the lower areas for farming. Over the past century, the expansion of human activities and agricultural production has forced Skywalkers to move higher, from 700 meters of elevation to more than 1,700 meters, Fei said.

A 2011 study by a team led by Fan Pengfei found that the number of Skywalkers in five areas in Gaoligong, including Nankang, declined 50% in 20 years. The animals completely disappeared in nine other areas. Agricultural development, logging, and poaching were the main factors, according to the study.

Since the 1980s, local authorities have encouraged farmers to grow tsaoko, a densely growing plant whose dried fruit is also known as black cardamom, in an effort to bolster farmers’ incomes and alleviate poverty. Tsaoko plants mainly grow under the forest canopy, which is believed to have a limited impact on the forest. But scientists said growing tsaoko led to the removal of taller trees to increase the forest floor’s sunlight penetration, making it more difficult for gibbons to travel and find food.

Researchers have found 51 Skywalkers living in 20 groups within the Gaoligong nature reserve, most of them in isolation, according to Zhang Fuyou, the deputy director of Baoshan Preservation Bureau in Gaoligong who has tracked the Skywalker gibbons since 2017.

By the end of 2021, most of the contracts signed between the local government and farmers for tsaoko planting in the reserve will expire, Zhang said, adding that “it will require a hefty investment” to restore the forest.

Outside the Gaoligong reserve, other habitats for Skywalker gibbons face similar problems. In Yingjiang County, bordering Myanmar, about 80 gibbons were found living in 22 groups in 2017. But the gibbon groups were dispersed and separated, while also being threatened by human activities, said Zhang Lixiang, a local preservation official.

Extinction vortex

Skywalker gibbons are born with white fur, which gradually turns gray or black depending on their sex. They can live as long as 30 years, reaching sexual maturity between the ages of 8 to 10. Females give birth around every four years, producing only one infant.

The low fertility rate makes efforts to increase the Skywalkers’ population extremely difficult.

In late 2007, Li Jiahong found that Azhen lost her first child, probably due to attacks by other animals. In 2012, Azhen had a second child, a female named Hope by researchers. But in July 2018, Hope was found dead. An autopsy showed that Hope died because of multiple organ failures, indicating potential genetic disease.

Scientists collected stool for genetic studies and found that the three adult gibbons in Nankang — Azhen, Quiff, and Partheno — were close relatives, probably having the same grandmother. Inbreeding has made the gibbons more likely to suffer genetic diseases, scientists said.

Inbreeding many years ago started reducing the genetic diversity of gibbon groups in several habitats in Gaoligong, Fan said, based on his studies.

Isolated habitats, shrinking populations, and inbreeding are pushing Skywalker gibbons to the brink of an extinction vortex, a scenario in which environmental, genetic, and demographic forces interact over time to push a population toward extinction.

According to Fei, there are at least 10 single adult Skywalker gibbons that are unable to find a mate, like Partheno. And at least three families are living in isolation like Azhen and her partner.

“Extinction is very likely,” Fei said. Without intervention, gibbon families currently living in isolation will disappear in about 30 years, while others won’t last any longer, Fei said.

Scientists are studying various methods to help Skywalkers interbreed and share genes. One proposal is to anesthetize and capture gibbons to move them to other habitats. But experts are highly cautious about such measures because of risks associated with anesthesia and transport that may harm the gibbons in the process.

Another plan being reviewed is to build corridors and pathways to help them migrate and find new partners. But that plan also faces implementation challenges because of Yunnan’s complicated geography.

In 2018, scientists started testing an innovative program using satellite telephones to broadcast Skywalker songs across regions to help them communicate and encourage them to find each other.

Early experiments with Partheno sparked hopes as she responded excitedly to songs from another gibbon through the phone broadcasts.

Encouraged by the results, scientists set up a call between Partheno and a male gibbon living 20 kilometers away named A1. The pair excitedly chatted through the connection and started to look for each other. Following Partheno’s songs and voice recordings, A1 started moving beyond his habitat.

With the sound guidance, the best scenario would have been for Partheno and A1 to move toward each other and eventually meet in a new habitat, Fei said.

“The sounds would let them know there is hope and encourage them to keep moving,” he said.

But reality is more challenging. Due to gibbons’ caution and the long distance, it could take at least three years or more for Partheno and A1 to find each other, even if their journeys went smoothly, according to Fei’s estimates.

After the rainy season in 2020, however, researchers lost track of Partheno. No one heard her songs again. Partheno was around 30 years old and probably died of old age, Li said.

“She waited and cried throughout her life, without any hope,” Li said.

Azhen and her partner are also getting old. They have a new baby known as Rice. After several years, Rice will become an orphan and the last Skywalker in Nankang, Li said.

Scientists are desperately searching for solutions to help the Skywalkers breed.

“We can wait, but those groups with tiny populations can’t,” one expert said.

There is still hope. After “chatting” with Partheno, A1 started his journey and left the habitat where he stayed for four years, researchers found. Although no gibbon has been detected in areas near him, A1’s search continues.

This article was originally published by Caixin Global. It has been republished here with permission.

(Header image: A Skywalker hoolock gibbon in the Gaoligong Mountains National Nature Reserve, Yunnan province, 2018. Magnus Lundgren/Wild Wonders of China via People Visual)