The potential for passive acoustic monitoring and automated detection to improve conservation efforts of tarsiers in Sulawesi, Indonesia

Dena Jane Clink , Johny Tasirin

Tarsiers are small, haplorrhine primates that occur in Southeast Asia. Tarsiers on the island of Sulawesi range from Vulnerable to Critically Endangered, and many are data deficient, which means there is a great need for improved monitoring approaches. Sulawesi tarsiers are pair-living, territorial, and engage in duets within human hearing range, which makes them ideal candidates for passive acoustic monitoring (PAM), an approach that relies on autonomous acoustic recording units. Here, we provide a proof-of-concept workflow that combines PAM, automated detection, and a simple occupancy modeling example to monitor Gursky's spectral tarsier (Tarsius spectrumgurskyae) in Tangkoko National Park, North Sulawesi, Indonesia. We used a custom trained BirdNET model deployed over ~520 hours of PAM data and manually verified all detections. Similar to previous work, we found that the majority of tarsier duet vocalizations occurred around sunrise, with a few vocalizations emitted in a non-duet context other times during the night. Using the true positive detections, we were able to create a detection history for occupancy modeling. Our simple occupancy modeling yielded occupancy and detection estimates consistent with expectations for the well-studied population at this site. We advocate that future work includes occupancy modeling across land use gradients, different forest types, and under different management regimes, to improve tarsier conservation efforts across Sulawesi. We provide the labeled training data and the trained model to facilitate future work.