“United by Urine: Do Chimps Strengthen Bonds While Peeing in Groups?”

Ena Onishi, a PhD candidate at Kyoto University, has dedicated over 600 hours to observing chimpanzees urinating. She has a solid rationale for this extensive observation, however. She is a member of a research team that recently identified that these primates tend to urinate when they observe other chimps doing the same.

In a research paper published on Monday in the journal Current Biology, Ms. Onishi and her fellow researchers detailed this occurrence, which they label contagious urination. Their finding prompts inquiries regarding the significance of urination in the social interactions of chimps and other primates.

Ms. Onishi initially noticed contagious urination in 2019 while studying chimps at the Kumamoto Sanctuary in Kyoto, Japan. “I was monitoring a group of captive chimpanzees for a separate research initiative, and I observed that they tended to urinate simultaneously,” Ms. Onishi stated. “It made me wonder, Could this behavior be similar to other contagious actions like yawning?” she elaborated, alluding to our inherent inclination to yawn upon seeing others do it.

To investigate, Ms. Onishi examined the sanctuary’s 20 chimpanzees, documenting over 1,300 instances of them urinating together. After analyzing the data, Ms. Onishi and her colleagues discovered that the chimps were indeed urinating in quick succession. They determined that the closer a chimp was to the original urinator, the higher the chance it would also join in. They also found that chimps of lower social standing were more prone to urinate when others did.

“This outcome was unexpected for us,” Ms. Onishi remarked. “It prompted fascinating queries about the social purpose of this behavior, which has been largely neglected for a significant time.”

The reason the chimps engage in this behavior remains unclear, but Ms. Onishi and her colleagues have several theories. “Contagious urination may support the strengthening of group bonds, enhancing overall social unity,” she stated. “It could facilitate a mutual readiness for collective actions. There are numerous potential explanations.”

Although the study focused on captive chimpanzees, many of whom were rescued from the biomedical research sector, it is unlikely that this behavior is exclusive to this particular group.

“When observing great apes in their natural habitats, it is common to see group members coordinating their actions closely,” said Martin Surbeck, an evolutionary biologist at Harvard University who explores the behavioral ecology of chimps and bonobos and was not part of the research.

Dr. Surbeck conveyed that he was not shocked to discover that the Kumamoto chimps exhibited contagious urination and that such behavior would not be surprising in the wild. “We may even observe it in other social species,” he commented.

While additional studies are required on contagious urination and its evolutionary implications, Ms. Onishi and her colleagues were thrilled to have gained so much knowledge through straightforward observation.

“There are countless insights to be gained from the everyday behaviors of animals,” Ms. Onishi noted.