Bridging the gap: assessing the effectiveness of rope bridges for wildlife in Singapore

Roads that dissect natural habitats present risks to wildlife, creating gaps or barriers which animals have to traverse in order to move within and between their habitats. Restoring habitat connectivity can be achieved naturally by planting trees and vines to reconnect forest gaps, or artificially by creating culverts for small ground vertebrates, building overpasses for large terrestrial animals, or installing canopy bridges for arboreal fauna. The 3-km Old Upper Thomson Road borders the eastern side of the Central Catchment Nature Reserve, the largest nature reserve in Singapore, and isolates it from neighbouring forest patches. To facilitate safe crossing for tree-dwelling animals such as the critically endangered Raffles' banded langurs (Presbytis femoralis) along Old Upper Thomson Road, two rope bridges were installed. We monitored the use of these rope bridges by vertebrates from April 2020 to August 2021 through surveillance cameras attached on one end of each bridge. A total of 64 118 videos were processed, with 6218 (9.70%) containing vertebrates. Seven species, including three primates, two squirrels and two reptiles, utilised the bridges to travel between the forests. In particular, Raffles' banded langurs made a total of 293 successful crossings. We have shown that these rope bridges are useful for arboreal species and can complement national efforts to restore connectivity in fragmented habitats.