Dominant baboons experience more interrupted and less rest at night

Sleep is a fundamental biological process.¹^,² The amount and quality of sleep individuals get can impact various aspects of human and non-human animal health,¹ ultimately affecting fitness.³ For wild animals that sleep in groups, individuals may disturb one another's sleep,⁴^,⁵ but this aspect of social sleep has been understudied due to methodological challenges.⁶^,⁷^,⁸ Here, using nighttime rest (absence of bodily movements) as a proxy for sleep, we test the hypothesis that an individual's social dominance affects nighttime rest in a troop of wild, highly hierarchical⁸^,⁹ chacma baboons (Papio ursinus). First, we show that the troop's nighttime rest (determined by 40 Hz acceleration data) is highly synchronized. Next, we link nighttime rest dynamics to daytime spatial networks and dominance hierarchy (from 1 Hz GPS data and direct observations). We show that baboon nighttime states (activity and rest) are more synchronized between similarly ranked individuals and, unexpectedly, that more dominant baboons experience more interrupted and less nighttime rest than lower-ranked baboons. We propose that this hierarchy effect is explained by higher-ranked baboons resting closer to more group members, which leads them to exert a greater influence on each other's nighttime behavior compared with lower-ranked individuals. Our study provides the first evidence for the impact of social hierarchies on aspects of sleep in a wild primate, suggesting that dominance status may impose trade-offs between social rank and the quality and quantity of sleep.