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By Clare Wilson

Kadoorie Farm and Botanic Garden

With a population that fell to just 25 individuals a few years ago, every Hainan gibbon counts. So when a 2014 landslide on China’s Hainan Island forced the last surviving members of the world’s most endangered primate species to make death-defying leaps across a gap in the forest canopy, conservationists lent them a hand by stringing ropes between the trees.

The plan worked. Although the gibbons (Nomascus hainanus) took six months to get used to the idea, most of them eventually used the rope bridges to cross the 15-metre gap, either swinging along, crawling upside down or sometimes balancing like tightrope walkers. Only the larger males didn’t need the ropes.

Gibbons are very reluctant to come down to the ground, so after the landslide, this group reached fruit trees by flinging themselves across the large gap above a rocky floor as much as 30 metres below. Although the researchers saw no accidents, they thought a fall would be deadly. “It was pretty scary to watch – my heart just popped out of my throat,” says Bosco Chan at the Kadoorie Farm & Botanic Garden in Hong Kong.

Mothers had to make the leap with their baby clinging on. “If the infant-carrying mother falls, that would have been two down out of 25,” says Chan.

Today there are thought to be about 30 gibbons on the island. Trees in the dangerous area have since regrown, but Chan says rope bridges are proving useful in helping other primates cross gaps between fragmented habitats.

Journal reference: Scientific Reports, DOI: 10.1038/s41598-020-72641-z