Mantled howler monkeys avoid humans in response to both worker presence and noise intensity in an agroforestry system.

Anthropogenic disturbances pose significant challenges for wildlife conservation, especially for threatened primates such as the mantled howler monkey (Alouatta palliata). We investigated whether and how human presence and noise influence the immediate movement responses of mantled howler monkeys inhabiting an agroforestry system in Los Tuxtlas, Mexico. Between January 2020 and April 2021, we recorded monkey and human locations, human activities, and A-weighted equivalent continuous sound pressure levels (LAeq) at 15-min intervals during 823 h of observation. Using generalized linear mixed models, we found that both the occurrence and magnitude of avoidance movement increased significantly with increasing worker numbers and sound pressure levels. Although movement increased throughout the day, movement direction relative to human location remained constant, suggesting that circadian patterns influence when, but not how animals respond to anthropogenic factors. Therefore, howler monkeys avoid human presence while maintaining their characteristic energy-conservative ranging patterns, suggesting a complex balance between risk avoidance and metabolic demands. Our findings have important implications for wildlife management in agroforestry systems, as even relatively low levels of human presence (approximately one person per hectare) and noise (ranging from 40 to 85 dB) can trigger behavioral responses.