The effectiveness of artificial canopy bridges for the diurnal primates within a hydroelectric project in North Sumatra-Indonesia

Abstract

Primates that live within fragmented and disturbed habitat are facing population declines and a higher probability of extinction due to gene flow inhibition. To address this problem, land managers, practitioners, and primatologists have applied several approaches to enhance primates’ habitat quality and connectivity through habitat restoration and canopy bridge installation. In some cases, artificial canopy bridges have shown to be effective to facilitate movement between fragmented habitats for several primates’ taxa. However, while several types of canopy bridge designs are available, there is no clear evidence on which is the best for primates. Here we evaluated the effectiveness of three artificial canopy bridge designs within a hydroelectric project in Sumatra, Indonesia from 2019 to 2021. The hydroelectric project was located at the edge of a forest block within the Batang Toru Ecosystem which could disconnect the primate’s population from this protected forest to the other forest blocks. During 595 days of camera trapping, we captured 988 independent crossing events from six diurnal primate species (Pongo tapanuliensis, Hylobates agilis, Symphalangus syndactylus, Presbytis sumatrana, Macaca nemestrina, and Macaca fascicularis). Our initial observation finds the ladder canopy bridge design was commonly used by primates and Presbytis sumatrana was the species that often crossed the canopy bridge. These findings are important to improve species management plans and primate conservation in Indonesia.