Chimpanzee sleep patterns studied in Uganda

A recent study on chimpanzees in Uganda has for the first time recorded their sleep behavior in their natural habitat. Researchers observed that dominant males sleep less when other males or females in sexual activity are present, possibly to monitor rivals or mating opportunities.

Study location and group size

The research focused on the Sonso community of chimpanzees in the Budongo forest, a group that has been observed daily for over thirty years. This community, covering about 6 square kilometers, includes approximately 70 individuals, with 10 adult males.

Methodology for tracking sleep

To measure sleep in wild chimpanzees, researchers followed individuals from dawn until dusk, when they built their nests for the night. Using telescopic poles, they placed trap cameras inside the nests to film the chimpanzees’ sleep. The study recorded 116 nights across 35 individuals of varying sexes and ages, measuring total sleep time, fragmentation, and awakening times.

Sleep duration and behaviors

The study found that chimpanzees sleep an average of nine hours and thirty minutes per night, with significant variation between individuals. Like humans, they sleep on their side or back, but often sit upright when it rains. On average, they wake up three times per night to urinate, vocalize with relatives, or nibble on leaves.

Dominant males sleep less

Dominant male chimpanzees sleep less than other males, averaging eight and a half hours per night compared to nine and a half hours for non-dominant males. Their sleep duration decreases as more males are present in the group, while the opposite effect is seen in subordinate males.

Female presence affects male sleep

The presence of a female in estrus disrupts male sleep, leading to later nest construction, shorter sleep time, increased fragmentation, and earlier awakenings. This suggests that males may be sacrificing sleep to improve their chances of mating during or after the night.

Implications for cognitive and emotional health

The study raises questions about the potential impact of reduced sleep on cognitive and emotional functions. In humans and rodents, short or fragmented sleep is known to impair these functions, though some individuals may compensate with daytime naps or genetic adaptations.

Comparisons with other primates

Studies on other primates, such as baboons and geladas, show similar patterns where dominant individuals sleep less. Larger group sizes are also associated with shorter and more fragmented sleep in species like orangutans and baboons. In humans, it is believed that our ancestors faced similar trade-offs, possibly due to the use of fire, which extended social interactions at the cost of sleep.