Kadoorie Farm and Botanic Garden

For animals that spend most of their lives high in the trees, gaps in the forest might as well be the Grand Canyon. These chasms are especially hard on gibbons; although larger males can leap across some canopy gaps, females and juveniles can be cut off from food, companions, and even potential mates. Now, a new study suggests a couple of sturdy ropes could literally help bridge the gap.

Gibbons are at risk of extinction across Southeast Asia, largely because of habitat loss. With just 30 individuals left, the Hainan gibbon (Nomascus hainanus) is considered the rarest primate on Earth. All of these animals live on the Bawangling National Nature Reserve in Hainan, an island province in southern China. In July 2014, a typhoon caused landslides across the reserve, creating gaps in the forest canopy that were difficult for these primates to cross.

To help reconnect the habitats, professional tree climbers installed an artificial “bridge” across a 15-meter-wide gully, made of two mountaineering-grade ropes. Nearly 6 months later, the gibbons started to use the bridge to traverse the gully, researchers report today in Scientific Reports. The team documented 52 crossings in a group of eight gibbons, with most walking along one rope while holding on to the second rope for support, which the scientists dubbed “handrailing.” The gibbons also shimmied underneath the ropes using all limbs (like sloths) and swung along the ropes using just their arms.

Conservationists previously built artificial bridges to help other treebound species such as the Bornean orangutan and the Javan slow loris. And both the lar and western hook Gibbon cross forest gaps. But this is the first example of the rare Hainan gibbon using them. The rope bridges could be a short-term solution to reconnect disjointed habitats, the researchers argue, coupled with efforts to replenish natural forest cover.

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