More dominant baboons have less and lower quality sleep

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, we test the hypothesis that individual’s social dominance can affect sleep opportunities, by studying sleep patterns in a troop of wild chacma baboons ( Papio ursinus ), a species with a strong hierarchical social structure. First, we show that the troop’s night-time sleep (determined by 40Hz acceleration data) is highly synchronised. Next, we link night-time sleep dynamics to daytime spatial networks and dominance hierarchy (from 1Hz GPS data and direct observations). We show that baboon sleep synchrony is higher between similarly ranked individuals, and unexpectedly, more dominant baboons experience less and lower-quality sleep. 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 other’s 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.