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The Last 37: Repopulating the Critically Endangered Hainan Gibbon

A smart digital solution is giving hope to the survival of the world's rarest primate, just 37 of which remain in existence

Covering 4,269 km2, Hainan Rainforest National Park is located in the center of Hainan Island in the South China Sea.

Home to China's largest tropical rainforest, the island is known for its rich biodiversity. Within the national park, the verdant jewel of Bawangling stands out for its abundance of natural genetic resources, including the Hainan black-crested gibbon (Nomascus hainanus).

Hainan Tropical Rainforest National Park Bawangling official website

Image source: Hainan Tropical Rainforest National Park Bawangling official website

Listed as 'critically endangered' by International Union for Conservation of Nature (IUCN), the Hainan gibbon is the world's rarest and most endangered primate. With just 37 individuals remaining as a cumulative consequence of hunting and habitat destruction, repopulation has proven to be extremely difficult. Juvenile gibbons take between six and eight years to reach sexual maturity, and the primate's average breeding cycle lasts two years. Moreover, it is impossible to raise them in captivity as the species is arboreal in nature (meaning they live in trees).

To encourage them to reproduce on their own, local authorities have been seeking to restore the local ecosystem by, for example, planting the types of fruit trees and plants that the frugivorous gibbon prefers, like figs and lychees.

To better protect the remaining individuals and help repopulation efforts, conservationists need to understand the primate's behaviors and accurately track and monitor individuals. However, given the elusive nature of the slender gibbons, which use their powerful arms to swing from tree to tree high up in the forest canopy, doing so is far from easy.

The song of an endangered species

Hainan gibbons display a unique set of behaviors, including how they communicate. With male and female pairs known for performing a daily 'duet' each morning, their vocalizations are invaluable for providing detailed analytical data on behaviors, distribution, threats, and the effects of conservation efforts.

The songs of an endangered species

Image source: Hainan National Park Research Institute

Using manual methods, recording gibbon song usually requires researchers to camp overnight in Bawangling's mountains. As the Hainan gibbon is both alert and accustomed to moving fast high in the forest canopy, researchers struggle to pinpoint their location, frequently missing their morning calls and having to wait until noon or evening for another chance. Additionally, the offline equipment used for collecting voiceprints can only store data for 15 days, whereas the researchers generally visit the mountain once every three months to complete patrols and collect voice samples.

The various obstacles have made it extremely difficult to perform audio-monitoring with meaningful outcomes.

The team needs to rely on heavily on luck and so monitoring efficacy is very limited. Wei Fuliang
Hainan Gibbon Monitoring Team

At the end of 2021, Huawei, IUCN, and Hainan National Park Research Institute embarked on a pilot project under the IUCN-Huawei Tech4Nature initiative to develop and deploy a real-time monitoring solution. Comprising audio-monitoring devices connected by a wireless network to a cloud platform equipped with smart analytics capabilities, the devices can transmit audio data to cloud 24/7 over a period 90 days.

Processed by an algorithm trained with existing research data, many gibbon calls that were difficult to identify can now be successfully extracted and analyzed, with current recognition accuracy reaching 89.2%.

Huawei's digital solution automatically identifies and classifies their vocalizations, opening the gateway to potentially creating a unique voiceprint for each gibbon and establishing a database of invdividuals. This would enable researchers to monitor young individuals in the group and help staff track whether lone adults are reproducing or have established families outside of the fixed group.

The project partners have high expectations that the smart solution can tip the balance in nature's favor and prevent the extinction of this distinctive and extremely vulnerable primate.