Bridging gaps in rare gibbon’s habitat

The Hainan gibbon (Nomascus hainanus) is the rarest primate on Earth, with no more than 30 individuals thought to remain in a single patch of increasingly divided forest on China’s Hainan Island. 

In an attempt to bridge these growing gaps in habitat, and help boost dwindling species numbers, researchers led by Bosco Pui Lok Chan, from Kadoorie Farm and Botanic Garden in Hong Kong used a seemingly simple solution – a rope bridge.

“We constructed the first canopy bridge for Hainan gibbon in 2015 to facilitate passage at a natural landslide; mountaineering-grade ropes were tied to sturdy trees with the help of professional tree climbers and a camera trap was installed to monitor the wildlife usage,” the authors write in a paper in the journal Scientific Reports.

“The canopy bridge monitored was used for crossings in both directions, and both females and juveniles could initiate crossing.” 

The researchers report that the primates took some time to get used to the bridge, and only started using it after 176 days. However, that frequency gradually increased once they became more familiar with crossing. 

Over the 470-day study, 208 photographs and 53 videos were captured showing the gibbons using climbing movements along the rope. All nine were recorded using the canopy, except for the adult male and larger juveniles, which instead opted to leap across the forest gaps. 

The camera traps also recorded other animals, including Pallas’s squirrel (Callosciurus erythraeus), a small flying squirrel (Hylopetes sp.) and a small rodent from the subfamily Murinae.

While this is a first for the Hainan gibbon, artificial crossings of various design are being used as a conservation measure worldwide. For example, in Western Australia a rope bridge was installed across a major road so western ringtail possums could cross safely.

Forest fragmentation can be particularly detrimental to arboreal animals as gaps in the canopy affect dispersal, foraging and breeding opportunities. The gaps also force them to travel on the ground increasing their vulnerability to predators, diseases, and accidental fatalities such as roadkill.

While the Hainan study highlights the value of such strategies as artificial bridges, the researchers maintain that restoring forests should be the priority. 

“We recommend building canopy bridges at the early stages of a forest gap restoration project to provide temporary connectivity, but reforestation with fast-growing native trees should also be simultaneously carried out as a long-term solution…,” they write.