Rank and social context influence sleep in wild chimpanzees

Sleep is vital for health and fitness, and its expression is shaped by ecological and social contexts that may either promote or disturb it. Most research, however, has focused on captive settings, detached from natural environments that can modify the balance between benefits and drawbacks of sleeping in a group. Using direct recording of sleep using a custom-made, infrared remote camera, mounted on a telescopic pole s, we examined the impact of social rank and context on sleep in wild chimpanzees in Uganda. High-ranking males experienced shorter, more fragmented and less efficient sleep than subordinates. Party composition also influenced sleep: whereas sleeping in groups generally prolonged sleep duration and reduced wake-bout durations compared to sleeping alone, increasing the number of adult males in the sleeping party delayed nesting time and reduced sleep duration in high-ranking individuals. The presence of sexually active females delayed nesting time and advanced waking time in males, tended to reduce sleep duration and increased sleep fragmentation. These findings emphasize the need to study sleep in ecological contexts to gain a deeper understanding of the trade-offs shaped by social dynamics in sleep patterns.