Ena Onishi, a doctoral student at Kyoto University, has spent over 600 hours watching chimpanzees urinating. She has a good reason for all that peeping, though. She is part of a team of researchers that recently discovered that the primates tend to tinkle when they see nearby chimps do the same.

In a study published Monday in the journal Current Biology, Ms. Onishi and her colleagues described this phenomenon, which they call contagious urination. Their discovery raises questions about the role peeing might play in the social lives of chimps and other primates.

Ms. Onishi first spotted contagious urination in 2019 while observing chimps at the Kumamoto Sanctuary in Kyoto, Japan. “I was observing a group of captive chimpanzees for a different research project, and I noticed that they tended to urinate at the same time,” Ms. Onishi said. “It got me thinking, Could this be one of those contagious behaviors like contagious yawning?” she explained, referring to our innate tendency to yawn upon seeing or hearing others do it.

To find out, Ms. Onishi studied the sanctuary’s 20 chimpanzees, observing them peeing together over 1,300 times. After crunching the numbers, Ms. Onishi and her colleagues realized that the chimps were indeed urinating in rapid succession. They found that the nearer a chimp was to the initial urinator, the more likely it was to join the party. They also discovered that chimps lower on the social ladder were more likely to go when others were going.

“This result was surprising for us,” Ms. Onishi said. “It raised intriguing questions about the social function of this behavior, which has been overlooked for a long time.”

Why the chimps do this remains a mystery, but Ms. Onishi and her colleagues have several hypotheses. “Contagious urination might help reinforce group connections, boosting overall social cohesion,” she said. “It could promote a shared readiness for collective behaviors. There are so many possibilities.”

Although the study was limited to captive chimpanzees, many of them rescued from the biomedical research industry, the chances that this behavior is unique to this group are low.

“If you walk with great apes in the wild, you often see that group members really coordinate what they’re doing,” said Martin Surbeck, an evolutionary biologist at Harvard University who studies the behavioral ecology of chimps and bonobos and was not involved in the research.

Dr. Surbeck said that he wasn’t surprised to learn that the Kumamoto chimps were engaging in contagious urination and that the behavior wouldn’t be unexpected in the wild. “We might even see it in other social species,” he said.

While more research is needed on contagious urination and its evolutionary function, Ms. Onishi and her colleagues were delighted that they had learned so much through simple observation.

“There is a myriad of things to be discovered from the daily activities of animals,” Ms. Onishi said.

President Trump on Monday signed an executive order to withdraw the United States from the Paris Agreement, the pact among almost all nations to fight climate change.

By withdrawing, the United States will join Iran, Libya and Yemen as the only four countries not party to the agreement, under which nations work together to keep global warming below levels that could lead to environmental catastrophe.

The move, one of several energy-related announcements in the hours following his inauguration, is yet another about-face in United States participation in global climate negotiations. During his first term Mr. Trump withdrew from the Paris accord, but then President Biden quickly rejoined in 2020 after winning the White House.

Scientists, activists and Democratic officials assailed the move as one that would deepen the climate crisis and backfire on American workers. Coupled with Mr. Trump’s other energy measures on Monday, withdrawal from the pact signals his administration’s determination to double down on fossil-fuel extraction and production, and to move away from clean-energy technologies like electric vehicles and power-generating wind turbines.

“If they want to be tough on China, don’t punish U.S. automakers and hard-working Americans by handing our clean-car keys to the Chinese,” said Gina McCarthy, former White House climate adviser and former head of the Environmental Protection Administration. “The United States must continue to show leadership on the international stage if we want to have any say in how trillions of dollars in financial investments, policies and decisions are made.”

On Monday Mr. Trump also signed a letter to the United Nations, which administers the pact, notifying the world body of the withdrawal. The withdrawal will become official one year after the submission of the letter.

U.S. efforts to reduce greenhouse gas emissions were already stalling in 2024, and Mr. Trump’s entry into office makes it increasingly unlikely the United States will live up to its ambitious pledges to cut them even further. Emissions dropped just a fraction last year, 0.2 percent, compared with the year earlier, according to estimates published this month by the Rhodium Group, a research firm.

Despite continued rapid growth in solar and wind power that was spurred by the previous administration’s signature climate legislation, the Inflation Reduction Act, emissions levels stayed relatively flat last year because demand for electricity surged nationwide, which led to a spike in the amount of natural gas burned by power plants.

The fact that emissions didn’t decline much means the United States is even further off-track from hitting Mr. Biden’s goal, announced last month under the auspices of the Paris Agreement, of slashing greenhouse gases 61 percent below 2005 levels by 2030. Scientists say all major economies would have to cut their emissions deeply this decade to keep global warming at relatively low levels.

In a scenario where Mr. Trump rolled back most of Mr. Biden’s climate policies, U.S. emissions might fall only 24 to 40 percent below 2005 levels by 2030, the Rhodium Group found.

“President Trump is choosing to begin his term pandering to the fossil fuel industry and its allies,” the Union of Concerned Scientists said in a statement. “His disgraceful and destructive decision is an ominous harbinger of what people in the United States should expect from him and his anti-science cabinet.”

Since 2005, United States emissions have fallen roughly 20 percent, a significant drop at a time when the economy has also expanded. But to meet its climate goals, U.S. emissions would need to decline nearly 10 times as fast each year as they’ve fallen over the past decade.

The United States is also a major exporter of emissions. Because of policies promoted by both Republicans and Democrats, the United States is now producing more crude oil and natural gas than any nation in history. Mr. Trump has vowed to further ramp up production and exports.

While the United States may not be party to the Paris Agreement, it will still be part of the U.N. Framework Convention on Climate Change, which hosts annual climate negotiations known as COPs. This year’s COP will be held in Brazil in November and nations will be announcing new pledges for emissions reductions.

One recent study by Climate Action Tracker, a research group, found that, if every country followed through on the pledges they have formally submitted so far, global average temperatures would be on track to rise roughly 2.6 degrees Celsius, or 4.7 degrees Fahrenheit, above preindustrial levels by the end of the century, well above the 1.5 degrees Celsius the Paris Agreement originally set as a goal.

“Trump’s irresponsibility is no surprise,” said Christiana Figueres, a Costa Rican diplomat and an architect of the Paris Agreement in 2015. “In time, Trump will not be around but history will point to him and his fossil fuel friends with no pardon.”