Into the night: camera traps reveal nocturnal activity in a presumptive diurnal primate, Rhinopithecus brelichi

A study at Fanjingshan National Nature Reserve, China, reveals that the Guizhou snub-nosed monkey (Rhinopithecus brelichi), typically considered a strictly diurnal primate, exhibits significant nocturnal and twilight activity. Using 24-hour camera traps over two periods in 2011, researchers standardized time data to account for geographic coordinates, demonstrating that these monkeys adjust their activity patterns opportunistically to maximize energy intake amid fluctuating day lengths and food resources in temperate environments. The findings challenge the assumption of strict diurnality among anthropoids, except owl monkeys, and highlight the adaptability of primate behavior under varying ecological conditions. Additionally, the study underscores the utility of camera traps in primate research and advocates for standardized time data to facilitate cross-study comparisons.

Tan, C. L., Yang, Y., & Niu, K. (2012). Into the night: camera traps reveal nocturnal activity in a presumptive diurnal primate, Rhinopithecus brelichi. Primates, 54(1), 1–6. https://doi.org/10.1007/s10329-012-0318-2