Reliable density estimates of threatened species provide important information on their conservation status and effectiveness of conservation efforts. Here, we provided the first density estimates that utilize detection probability of four hornbill species in Ketambe Research Station area, Leuser Landscape. Moreover, we made a preliminary investigation of the relationship between hornbill detections and fruit availability. We conducted line transect and phenology surveys during July-September 2019. Our findings highlighted the importance of Ketambe as a stronghold for hornbill populations, indicated by relatively higher density estimates of four species (Wreathed Hornbill Rhyticeros undulatus, Rhinoceros Hornbill Buceros rhinoceros, Bushy-crested Hornbill Anorrhinus galeritus, and White-crowned Hornbill Berenicornis comatus) than elsewhere. We noted the lack of Helmeted hornbill detections which might be due to illegal poaching. Further, we identified the positive influence of ripe fruit supplies on hornbill presence. Our study presented the baseline density data for future hornbill population monitoring studies. We also recommended conducting studies of hornbill diet and foraging behaviour and their responses to human disturbances.

Reliable density estimates of threatened species provide important information on their conservation status and effectiveness of conservation efforts. Here, we provided the first density estimates that utilize detection probability of four hornbill species in Ketambe Research Station area, Leuser Landscape. Moreover, we made a preliminary investigation of the relationship between hornbill detections and fruit availability. We conducted line transect and phenology surveys during July-September 2019. Our findings highlighted the importance of Ketambe as a stronghold for hornbill populations, indicated by relatively higher density estimates of four species (Wreathed Hornbill Rhyticeros undulatus, Rhinoceros Hornbill Buceros rhinoceros, Bushy-crested Hornbill Anorrhinus galeritus, and White-crowned Hornbill Berenicornis comatus) than elsewhere. We noted the lack of Helmeted hornbill detections which might be due to illegal poaching. Further, we identified the positive influence of ripe fruit supplies on hornbill presence. Our study presented the baseline density data for future hornbill population monitoring studies. We also recommended conducting studies of hornbill diet and foraging behaviour and their responses to human disturbances.