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A rope bridge restored a road between the trees for endangered gibbons

With acrobatic jumps, Hainan gibbons can cross a large ravine sculpted by a 2014 landslide in the forest of China’s Hainan Island. But when a palm frond trapped by the vaulted monkeys to fix their landing began to fall, the researchers rushed to offer a safer route.

Despite being slow to adopt it, the gibbons increasingly traversed a bridge made of two ropes that was installed along the 15-meter distance, researchers reported on Oct. 15 in Scientific Reports. The discovery suggests that such moorings could also help connect intact forests that have been fragmented by human activities and aid conservation efforts of these and other canopy dwellers.

"Fragmentation is becoming a growing problem," says Tremaine Gregory, a conservation biologist at the Smithsonian's National Zoo and Conservation Biology Institute in Washington, D.C., who did not participate in the study. "It will probably be, along with climate change, one of the biggest challenges for biodiversity in decades."

The landslide damaged a tree-lined road, a preferred route through the trees the monkeys use to traverse the rainforest. Hainan's gibbons (Nomascus hainanus) are almost strictly arboreal, and forest fragmentation can divide already critically endangered primates (SN: 8/6/15) into smaller breeding populations, says Bosco Chan, a farm conservation biologist and botanical gardener. of Kadoorie in Hong Kong. This can lead to inbreeding or the extinction of local groups.

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Only about 30 individuals of this species remain, all living in a nature reserve on Hainan Island. For the group of nine gibbons studied, the researchers did not want the animals to be injured by crossing the gap.

Enter the rope bridge. The gibbons took months to catch, but about 176 days after the bridge was installed, the camera traps caught the gibbons leading to the ropes. “I was very excited when (the gibbons) started using it,” Chan says.

Hainan gibbons use a rope bridgeTo cross a ravine created by a landslide, some Hainan gibbons hang and swing from a rope bridge installed by the researchers, while others walk across, sometimes using the upper rope as handrails.Kadoorie Farm and Botanical Garden

Finally, the scientists observed the gibbons crossing the bridge with the frequency with which the animals traversed that stretch of forest before the landslide. Females and juveniles preferably used the bridge, while an adult male never used it and almost adult juveniles rarely did.

Although scientists expected the animals to swing under the bridge using their arms, Chan says, many preferred to walk as if it were a loose rope, using a rope as a handrail or climbing the ropes using all limbs. From time to time, the gibbons ran without enduring. For now, the bridge offers a temporary solution as transplants from native trees grow and other trees regenerate.

Such man-made bridges provide a sensible and innovative approach to helping gibbons move safely, says Susan Cheyne, a primatologist based in Oxford, England and vice president of the Small Monkeys Section of the International Union for Conservation of Nature, who advised the Hainan project. . "We want them to stay in the canopy." On the ground, gibbons can be hit by cars, fight dogs, or be exposed to parasites not normally found by animals.

Moreover, the adoption of the bridge by Hainan gibbons suggests that it is a "tool that other primate conservation groups could use," says Cheyne, as these gibbons are a "relatively fickle species. They are not too interested." In using new things, ”he says.

Beyond primates, other animals can also use these types of crosses. The team also saw how two squirrels and another rodent used the bridge. Depending on where the canopy bridges are located, marsupials or rodents could benefit, although observing these creatures to know for sure could be a challenge if they are nocturnal.

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