Dominant baboons experience more interrupted and less rest at night

The amount and quality of sleep individuals get can impact various aspects of human and non-human animal health, ultimately affecting fitness. For wild animals that sleep in groups, individuals may disturb one another, influencing sleep quality and quantity, but this aspect of social sleep has been understudied due to methodological challenges. Here, using nighttime rest (absence of bodily movements) as a proxy for sleep, we test the hypothesis that individuals social dominance can affect sleep opportunities by studying a troop of wild chacma baboons (Papio ursinus), a species with a strong hierarchical social structure. First, we show that the troops night-time rest (determined by 40Hz acceleration data) is highly synchronised. Next, we link night-time rest dynamics to daytime spatial networks and dominance hierarchy (from 1Hz GPS data and direct observations). We show that baboon rest synchrony is higher between similarly ranked individuals, and unexpectedly, more dominant baboons experience less and lower-quality rest. We propose that this hierarchy effect is explained by higher-ranked baboons resting closer to more group members, which also leads them exerting greater influence on each others night-time behaviour compared to lower-ranked individuals. Our study provides the first empirical evidence for the impact of social hierarchies on sleep in a wild primate, suggesting that dominance status may impose trade-offs between social rank and the quality and quantity of sleep.