Scientists in Myanmar listened in on the love songs sung by Skywalker gibbons (Hoolock tianxing) to find the largest known population of the endangered primate. Every morning, skywalker gibbon couples will wake up and sing to each other, with their voices echoing across the forest canopies. The love songs helped scientists confirm a hunch that the southeast Asian nation has the world’s largest population of Skywalker gibbons. The discovery is described in a study published February 14 in the International Journal of Primatology.

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“We were able to genetically identify 44 new groups of Skywalker gibbons in Myanmar,” study co-author and University of California, Davis wildlife veterinarian and epidemiologist Tierra Smiley Evans said in a statement. 

These primates are technically called Skywalker hoolock gibbons and were named by a group of Star Wars-loving scientists in 2017, after observing them in southwestern China. The gibbons are omnivores, but most of their diet comes from plants and not animals. According to the New England Primate Conservancy, figs are their favorite food to eat and they will also eat spiders and the occasional bird or chicken egg. They are about 32 inches tall on average and weigh between 13 and 15 pounds. 

A par of Eastern hoolock gibbons
Skywalker gibbons were found in areas previously thought to be occupied by the Eastern hoolock gibbons, like this pair. CREDIT: Peng-Fei Fan.

While the exact number of individual Skywalker gibbons is still unknown, they were found in areas previously thought to be occupied by the Eastern hoolock gibbon. Some 2013 population estimates suggested that there may have been up to 65,000 gibbons in the area where the Skywalkers have now been identified. 

While these new groups are the largest probable population of Skywalker gibbons in one place, scientists believe that today’s numbers are lower due to limited protected areas, hunting, and 

political unrest in Myanmar.

Silly love songs

Skywalker gibbons can’t swim, so rivers often form natural boundaries for them. This led the team to theorize that Skywalkers likely extended between two rivers to the west and another river to the east in Myanmar. 

Between December 2021 and March 2023, a local field team in Myanmar built acoustic monitoring systems that they used to listen in on the songs that Skywalker gibbons sang to each other every morning  to wake up. They recorded their duets, solos, and when each song started and ended. 

The team then collected chewed plants and fruits from the monkeys. This noninvasive way of sampling DNA allowed the team to genetically confirm that these were left by Skywalker gibbons. 

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They used photographs to scan for the physical characteristics that distinguish Skywalker hoolock gibbons and other hoolock species. Skywalkers have thinner eyebrows, a black or brown beard instead of a white one, and incomplete white face rings on the females. 

Threat assessment surveys in 12 villages were also conducted to gather critical local knowledge about the gibbons and the threats they face. 

An adult male Skywalker gibbon hangs from a tree branch.
An adult male Skywalker gibbon hangs from a tree branch. Genetic analysis of chewed plants confirmed the previously unknown population of Skywalkers in Myanmar. CREDIT: Peng-Fei Fan.

“Biologists did not believe Skywalker gibbons could live in the small remaining patches in Southern Shan State before we started this project,” study co-author and executive director of Nature Conservation Society Myanmar said in a statement. “I am delighted with our field team members who have done an excellent job, within a short period of time, building community trust for further conservation actions. This area is degraded forest. It is really important for Myanmar and China to consider extending conservation approaches for the Skywalker gibbon to this new geographic area.”

Should Skywalker gibbons remain endangered?

The team hopes that the new findings will help guide updates for the International Union for the Conservation of Nature’s (IUCN) Red List of Threatened Species. While the population estimates of Skywalker gibbons is higher than previously believed, ongoing habitat loss, degradation, and human conflict in Myanmar are a continued threat to the species. The authors believe that they should retain their Endangered designation on the IUCN Red List and that its habitat should be considered for protected area status.

“We found Skywalker gibbons in two regions of Myanmar: Kachin State and as far south as Shan State, in degraded forests and at much lower elevations than we expected, showing us they’re highly adaptable,” Smiley Evans said. “There needs to be a protected area system there that focuses on them.”