Detectable call types in short-term passive acoustic monitoring of Atlantic forest and Caatinga primates

Arboreal primates rely heavily on acoustic communication, making them ideal candidates for passive acoustic monitoring (PAM). Here, we investigated the detectability of vocalisations from Alouatta belzebul, Callithrix jacchus, Saimiri spp, and Sapajus flavius in three fragments of Atlantic Forest and two fragments of Caatinga Forest in northeastern Brazil. We recorded each area for 48 h per month over 7 months, placing one audiomoth recorder at each site. Our results show that all species were detectable through PAM, with varying detection rates: 8/13 known call types for C. jacchus, 14/31 for S. flavius, 2/4 for A. belzebul, and 6/27 for Saimiri spp. Not all calls from their vocal repertoire were detected. Call detectability was influenced by species, habitat, time of day, and month. We emphasise the importance of considering behavioural, dietary, and home-range patterns when designing PAM protocols for primates. Our findings provide valuable insights for optimising PAM studies and highlight the need for continued basic research on vocal repertoire descriptions to improve conservation efforts.