For the first time, scientists have studied the sleep of chimpanzees in their natural habitat. Researchers in Uganda conducted a study on the Sonso community of chimpanzees in the Budongo forest, monitoring their sleep patterns over 116 nights with 35 individuals of different sexes and ages. The study found that chimpanzees sleep an average of nine hours and thirty minutes per night, with significant variation between individuals and nights. They sleep mainly on their side or back, and sometimes sit when it rains. They wake up on average three times per night for reasons such as relieving themselves, exchanging vocalizations, or eating leaves. Dominant males were found to sleep less than other males, averaging eight and a half hours per night compared to nine and a half hours for other males. Their sleep was also more fragmented. This may be due to their protective role in the group or increased vigilance against competition from other males. The sleep duration of dominant males was strongly modulated by the number of males present in the sleep group: the higher the number, the shorter their sleep duration. Subordinate males, in contrast, benefited from a sense of security in larger groups. The presence of a sexually active female in the sleep group disrupted the sleep of males, leading to later nest building, reduced sleep duration, increased fragmentation, and earlier awakening. This suggests that males are sacrificing sleep to optimize their chances of mating. The study also raises questions about the potential costs of reduced sleep on cognitive and emotional functions, as short and fragmented sleep is known to impair these in humans and rodents. However, it remains unclear how dominant males maintain high cognitive performance despite reduced sleep. Possible explanations include daytime napping or genetic adaptations, though these hypotheses require further investigation. Similar patterns of reduced sleep in dominant individuals have been observed in other social primates such as baboons and geladas. Studies on orangutans and baboons also suggest that larger group sizes correlate with shorter and more fragmented sleep. In humans, the findings may echo evolutionary trade-offs between sleep and social interactions, with humans sleeping less than other primates.