World's Rarest Primates Spotted Using Artificial Bridges For The First Time

Hainan gibbons started to use the canopy bridge 176 days after installation, which was most popular among females and small juveniles. Kadoorie Farm and Botanic Garden

An island in China is home to the world’s rarest primate, the Hainan gibbon (Nomascus hainanus). At a time where this elusive and critically endangered species is facing extinction, much work is being done to help them overcome their two greatest threats: hunting and habitat fragmentation. A new study published in the journal Scientific Reports is finally returning good news regarding one project trying to tackle the latter by building artificial bridges in the canopy to connect the fragmented forest. For the first time, Hainan gibbons have been caught on camera using the bridges, demonstrating that these artificial connections can serve as valuable highways for arboreal species.

Hainan gibbons are exclusively found in the forests of Hainan Island where they move around in the canopy. As the forest has become fragmented due to human interference and landslides, the gibbons have been forced onto the ground to move between trees, which increases their risk of predation. To avoid this danger, some populations are decreasing their home ranges, which limits foraging and breeding opportunities. Bad news for a species that could stand to benefit from a baby boom.

Adult female Hainan gibbons are golden yellow, while immature gibbons are black regardless of their sex and resemble an adult male. Kadoorie Farm and Botanic Garden.

"When we started work at the reserve in 2003, there were only 2 groups [of Hainan gibbons] with a total of 13 gibbon individuals left in the entire world," said researcher Bosco Pui Lok Chan in an email to IFLScience. "Since then, we have been implementing various conservation actions together with the local conservation authorities, including regular monitoring of the gibbon population, and we're recording a gradual recovery, with a third and fourth gibbon family group formed in 2011 and 2015, respectively. At the beginning of 2020, we confirmed the formation of a fifth group, and the world population has bounced back to over 30 individuals. So it shows the species is able to recover, and we should have hope.

Back in 2015, Chan and colleagues decided to try and bridge the gaps between these forest habitats by constructing an artificial canopy bridge. The goal was that Hainan gibbons would use the bridges to travel between separated forest habitats instead of needing to first reach the ground. The two areas of habitat were separated following a landslide that forged a 15-meter-wide (50-foot-wide) gully. This gap was closed by the researchers using mountaineering-grade ropes that were tied to sturdy trees and fitted with motion-sensor cameras to monitor wildlife usage.

 

It took 176 days before the Hainan gibbons decided to give the bridge a go, and over the total 470-day study period, the motion-sensor cameras captured 208 photographs and 53 videos of these incredibly rare animals using the rope bridge. The most common mode of locomotion across the bridge was climbing, followed by some very Tarzan arm swinging. Of the group of nine animals being monitored, almost all eventually used the rope except for one adult male who clearly preferred how things were done “in the good old days”. The youngest of the group were the most keen, while a few of the older juveniles opted to leap across the bridged gap along with the adult male.

The study joins wider research into the use of artificial bridges to connect the habitats of arboreal animals. In Java, water pipes are being used to make the canopy easier to navigate for slow lorises. The pipes come with the added benefit of irrigating surrounding coffee farms, inspiring farmers (some of whom once hunted these animals) to see these animals in a different light and support work trying to protect them. The support of the local human population has also been a huge benefit to research into the Hainan gibbons.

While a success, the artificial bridge wasn't a hit with everyone. Kadoorie Farm and Botanic Garden

"We have always tried to engage the local human population in the conservation of Hainan gibbon, and attempted a range of efforts such as public outreach programme including educational activities in local schools, training villagers living nearest to the gibbons in sustainable agriculture and eco-beekeeping to provide alternative livelihood rather than dependent on forest products, and employment of villagers to form a community monitoring team for the gibbons," said Chan. "These community monitoring members are now a core force in protecting and monitoring the gibbons. I would say these attempts collectively raised their awareness on the precarious situation of the Hainan gibbon, and instigates a sense of pride in the local community, and from the number of encounters with wildlife and birdlife during our fieldwork, I'd say these efforts contributed to the much reduced hunting pressure."

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