Chimps and Their Surprising Social Habit: The Contagious Nature of Peeing!

Peeing Is Contagious among Chimps

By Meghan Bartels edited by Sarah Lewin Frasier

Certain primates urinate concurrently. Ena Onishi was already aware of this—Japanese even features a term for when individuals accompany one another to the restroom: tsureshon. Nonetheless, Onishi became intrigued upon observing this conduct among the chimpanzees she was studying as a doctoral candidate at Kyoto University Wildlife Research Center. She was familiar with extensively examined “contagious” behaviors, such as yawning in humans, and questioned whether the chimps might be exhibiting “contagious urination.”

In a recent publication released on Monday in Current Biology, Onishi and her co-authors discovered that the adage “monkey see, monkey do” indeed seems to apply to these chimpanzees (even though they are not classified as monkeys). Even more captivating, each individual’s rank within the social hierarchy appears to affect who urinates and when. This finding marks the first recognized scientific investigation of contagious urination, as reported by the authors.

“It’s not something I would have ever considered studying, for sure,” remarks Matthew Campbell, a psychologist at California State University Channel Islands, who was not part of the new study but has researched contagious behavior in chimpanzees. “I found it clever and novel, and it raises many intriguing questions.”

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Onishi and her colleagues observed 20 chimpanzees, primarily males, that resided in four groups within Kyoto University’s Kumamoto Sanctuary from 2019 to 2021. The researchers collected over 600 hours of video recordings of the endangered primates, subsequently noting when each animal urinated and their locations during those times. “It was somewhat overwhelming because I wasn’t certain if I would obtain significant results or if all the hard work would ultimately yield nothing,” Onishi states. “It was indeed nerve-wracking at times!”

“On the surface, it may appear to be a trivial topic, but it truly addresses something that is quite fundamental.” —Matthew Campbell, psychologist

By juxtaposing the observations with computer-generated simulations of randomized urination, Onishi and her colleagues concluded that, indeed, the chimpanzees were more inclined to urinate within 60 seconds of each other than they would if behaving randomly. Proximity also played a role: animals situated just a few feet from the first chimp to urinate were significantly more likely to follow suit than those located 10 or more feet away.

However, perhaps the most fascinating analysis arose when Onishi and her colleagues examined the social connections among the chimpanzees that were urinating. They were taken aback to discover that a chimp who was friends with the initial individual to urinate was not any more likely to mimic that behavior. In contrast, a chimp that had a lower dominance status compared to the first to urinate was more susceptible to contagious urination.

“I initially anticipated that if social influences existed, they might resemble those observed in yawning—such as a stronger contagion among socially close pairs,” Onishi explains. “Instead, we noted a distinct effect of social rank, with lower-ranking individuals being more inclined to follow the urination of others.”

The recent paper serves merely as a preliminary report, indicating that substantial additional investigation is needed to grasp the phenomenon—and what insights it provides about the lives of chimpanzees. For instance, researchers could conduct a similar analysis with wild animals, although Onishi expects the outcomes would likely be comparable. Campbell also speculates whether the apparent synchronized urination led by dominant chimps simply reflects the group’s daily habits, wherein movements are orchestrated by the leading animal and may trigger a pre-journey restroom break.

Study co-author Shinya Yamamoto, a professor at Kyoto University, remarks that the revelation alters his perception of chimpanzees slightly. “This enhances my impression of chimpanzees as ‘social creatures,’” he notes. “This research illustrates that even their physiological characteristics are shaped by their social contexts.”

Campbell observes that depending on how accurately the behavior is conveyed between individuals, this finding might also assist in uncovering how a chimpanzee comprehends its own body and whether it possesses an understanding of urination. “The mechanics of this process and its implications for the cognitive life of a chimpanzee, that’s genuinely the fascinating aspect to me,” he adds. “At first glance, it may appear to be a trivial subject, but it actually delves into something that is fundamentally important.”