Javan slow loris.

Farming has fragmented the forest habitat of the Javan slow loris, but artificial bridges allow the primates to travel safely above developed land. Credit: Andrew Walmsley/NPL

Conservation biology

Bridges in the sky help slow lorises keep to the trees

Endangered primate cannot leap between isolated clumps of rainforest but can easily navigate artificial walkways.

Cautious primates called slow lorises can learn to traverse artificial bridges high above the ground, allowing the animals to move between patches of trees surrounded by farmland.

The Indonesian island of Java has lost more than 90% of its original forest, confining tree-dwelling creatures to fragments of rainforest. That poses a threat to animals such as the critically endangered Javan slow loris (Nycticebus javanicus). This primate cannot leap, so it must travel on the ground to reach unconnected trees, exposing it to predators and parasites.

Anna Nekaris at Oxford Brookes University, UK, and her colleagues installed seven bridges — some made from irrigation tubing — between disconnected patches of Javan forest and monitored the bridges’ use by seven Javan slow lorises. The primates took 13 days, on average, to venture onto the bridges, but then used them nightly. Lorises using the bridges added new feeding trees to their home ranges and spent less time travelling on the ground between trees.

The authors say that water-pipe bridges not only benefit canopy-dwelling creatures but also irrigate crops, helping to improve local farmers’ attitude towards wildlife.