Continuous Audio-Visual Sensor Monitoring Is More Effective Than Human Observers for Detecting Moor Macaques.

The number of species threatened with extinction is continuously increasing, underscoring the need for reliable population estimates to develop effective conservation plans. The ability to confirm a species' presence during surveys (i.e., detectability) is central for population estimates. While audio-visual sensors, like camera traps and passive acoustic monitoring (PAM), have emerged as valuable tools for monitoring primates, few studies have systematically compared their detectability, particularly in dense forests with limited visibility and for elusive species. Here, we compared 40-days continuous monitoring with audio-visual sensor (camera traps, N = 19; PAM, N = 7) versus human-based point transects with three survey visits (N = 20) on wild moor macaques (Macaca maura) in two different habitats: forest (N = 10) and open areas (N = 10). Using occupancy models to compare the detection probability (p), we found that camera traps (p = 0.63 ± 0.04) and PAM (p = 0.79 ± 0.08) outperformed point transects (p = 0.33 ± 0.07), regardless of habitat type. After equalizing survey time between methods, we found that detections were greater on point transects in surveys shorter than 1 day, but camera traps and PAM equalized their performance with two survey days (p-value < 0.05). Notably, combining both audio-visual sensors yielded the highest detectability (p = 0.87 ± 0.05). These results highlight the effectiveness of audio-visual sensors and support multi-method approaches for monitoring primates in tropical forests. Overall, this research contributes to designing more effective monitoring protocols for primate species, which are essential for planning conservation strategies.