Globally, primates are experiencing the pressures of anthropogenic influences altering natural landscapes. Given the interconnectedness of land use and species conservation, it is vital to understand how primates move within their environments and how they may respond to future land-use changes. Herein, we used unmanned aerial vehicle (UAV) vegetation surveys and direct behavioural observations to determine how living in a degraded forest has influenced a wild siamang group in northern Sumatra. Within this population, we found a high level of folivory, relatively infrequent territorial long calls, reused routes, and a preference for areas that corresponded with canopy topography high in elevation. These results show that forest degradation can affect the ranging patterns and land-use behaviour of siamangs. To conserve this species and others that display a comparable response to changes in their environment, we need to prevent further degradation before populations are separated and unable to adapt to the limitations that come with human-mediated landscape changes.