Thermal Drones in Primate Research: Field Applications to Detection Index.

Thermal infrared (TIR) imaging combined with drone technology offers a promising approach for primate monitoring, addressing limitations of traditional survey methods, though methodological validations remain necessary. From April 2022 to May 2023, manual and systematic TIR drone surveys were conducted in Cat Tien National Park, Vietnam, to evaluate their effectiveness in detecting and counting six sympatric diurnal primate species at sleeping sites. Detection success varied among species, with arboreal primates such as black-shanked douc langurs (Pygathrix nigripes) showing high reliability due to distinct thermal signatures, while gibbons and semi-terrestrial macaques were less reliably detected due to behavioral and ecological traits. A scoring system was developed to quantify detection reliability, providing a framework for evaluating multispecies studies.
Building on these findings, a Thermal Detection Index (TDI) was created to assess the suitability of TIR drones for monitoring 389 primate species. The TDI incorporates species-specific factors such as body mass, locomotion type, activity patterns, population densities, habitat use, and sleeping behaviors during diurnal and nocturnal surveys. A Global TDI Suitability Score was then established by integrating these indices with primate distribution data and climatic variables, including temperature, precipitation, and wind speed, to identify optimal species and regions for TIR drone-based monitoring. High-suitability regions were identified across Africa, Asia, and Latin America. Atelidae, Cercopithecidae, and Indridae families emerged as the most compatible for TIR drone surveys.
These findings highlight the potential of TIR drones for monitoring primates, particularly large-bodied arboreal species, while also addressing challenges posed by ecological and behavioral variability. This framework provides a valuable tool for prioritizing research efforts, identifying suitable species and regions for TIR drone-based monitoring, and advancing conservation strategies for primates worldwide.