Lights Out in the Canopy: Arboreal Camera Traps Offer New Insights Into Sleeping‐Site Partitioning and Sleep Ecology in Primate Communities

ABSTRACT Sleep is an essential yet costly biological process, leaving animals vulnerable to predation and constraining their use of space and time. Optimal sleeping sites therefore represent valuable, potentially contested resources, yet they remain largely overlooked in primate community ecology. Understanding how syntopic species compete for and partition sleeping sites can reveal mechanisms of coexistence, but community‐level studies remain limited because multiple arboreal species are difficult to monitor simultaneously. Here, we used arboreal camera traps to investigate sleeping‐site use and spatiotemporal partitioning within a Brazilian Atlantic Forest primate community. Over 7 months (2024–2025), we monitored ten Copaifera trapezifolia trees used as preferred sleeping sites by southern muriquis ( Brachyteles arachnoides ), brown howler monkeys ( Alouatta guariba ) and black‐tufted capuchins ( Sapajus nigritus cucullatus ), recording 4195 videos documenting 1253 visits and 158 sleeping nights. C. trapezifolia trees constituted a shared but limited resource, and access reflected predicted interspecific differences in resource holding potential (RHP), the relative ability of a species to prevail in direct contests over a shared resource. Muriquis and capuchins, the higher‐RHP species with larger home ranges, showed high temporal overlap in copaíba use—preferentially sleeping there on warmer nights and under lower lunar illumination, suggesting roles for thermoregulation and perceived predation risk—offset by reduced spatial overlap, consistent with greater ranging flexibility enabling spatial avoidance. Howlers, constrained by more restricted ranging and repeatedly displaced in direct encounters with the other species, instead relied on temporal segregation to access the same preferred trees. Nocturnal videos further revealed activity beyond residual wakefulness at the edges of the night, offering rare direct evidence of nocturnal behaviour and fragmented sleep in wild arboreal primates. These findings indicate that sleeping sites can function as contested, high‐value resources structuring primate community dynamics through asymmetric contest competition, and highlight arboreal camera trapping as a powerful tool for studying primate sleep ecology.