If you’ve ever counted to three before jumping into the pool with a friend, you’ve got something in common with dolphins. The sleek marine mammals use coordinated clicks and whistles to tell each other the precise moment to perform a backflip or push a button, according to new research. That makes them the only animals besides humans known to cooperate with vocal cues.

The new work is “fascinating,” says Richard Connor, a cetacean biologist at the University of Massachusetts, Dartmouth, who was not involved with the research. “We just see so much cooperation and synchrony [among dolphins] in the wild. This helps us understand how they accomplish that.”

Free-roaming dolphins are often in sync. They hunt in large groups and drive away rivals with coordinated displays. They can even match others’ movements down to their breathing patterns. But how do they achieve such synchronicity?

Scientists have long suspected the cetaceans coordinate their actions through vocal cues. Underwater microphones, called hydrophones, have been picking up their whistles and clicks for decades. But dolphins don’t open their mouths when they “talk,” and tracking underwater sound has long been a technical challenge.

So scientists have been developing ways to capture those sounds. In France, researchers recently combined five hydrophones to set up a star-shaped pattern that can pinpoint which dolphin in a group is “speaking,” says ethologist Juliana Lopez-Marulanda of Paris-Saclay University who co-developed the approach.

Meanwhile, Stephanie King, a behavioral biologist at the University of Bristol, and her colleagues at the Dolphin Research Center in the Florida Keys, have started using a similar, four-hydrophone setup with above-water video cameras to track sounds of synchronizing dolphins.

In two new studies, the teams used their equipment to help explain how the animals work together with such precision, in two very different situations.

A pair of bottlenose dolphins at the Dolphin Research Center in Florida

© Dolphin Research Center

At a theme park in Brussels, Lopez-Marulanda and colleagues found that trained dolphins doing backflips in sync touched the surface within one-thirtieth of 1 second of each other—even when starting out from opposite sides of their 30-meter-wide pool. “That was impressive!” Lopez-Marulanda says.

Meanwhile, King and her colleagues noted that bottlenose dolphins, who had to push buttons at the same time as a partner to get a treat, would often wait—sometimes up to 20 seconds—for their partner. Even when the animals were separated by more than 10 meters and couldn’t see each other, they still pushed their buttons within the same second.

In both scenarios, the hydrophones picked up what sounded like vocal cues. In Belgium, the dominant female sent a series of clicks that ended just milliseconds before each jump, while her partner made no noise, Lopez-Marulanda’s team will report next month in Behavioural Processes.

In Florida, the dolphins opted for series of whistles. They were 33% more likely to synchronize, and thus get the fish, when they whistled, the team reports today in Royal Society Open Science. They didn’t always whistle—and the study didn’t note whether they were also clicking. “But when they did whistle, they were consistently successful,” King says.

The scientists don’t yet know why some dolphins clicked and others whistled, nor why the whistlers didn’t do it every time. But the combined findings suggest dolphins use vocal communication to collaborate—a rarity in the animal world. Even nonhuman primates like chimpanzees use body language rather than sounds to cooperate, King says.

That doesn’t mean the dolphins actually “talk” to each other, cautions Shawn Noren, a physiological ecologist at the University of California, Santa Cruz, who was not involved in the study. Clicking, for example, is used for echolocation—figuring out how far an object is based on how long it takes for the clicks to echo back. (This can keep dolphins from hitting pool walls during jumps.) The animals are already known to “eavesdrop” on each other’s clicking in the wild, a behavior that potentially keeps them from “talking over each other,” Noren says. “So I’m not sure this means there was [intentional] communication here.”

Still, the studies provide “really important contributions” to understanding how highly social, big-brained dolphins work together so well, says Diana Reiss, a cognitive psychologist at Hunter College who was not involved with either project.

Further studies on how free-range dolphins coordinate could provide more insight, Reiss says, though following them through murky seas with high-tech equipment is tricky. In the meantime, the new studies provide “a really interesting glimpse into how dolphins might synchronize their behavior.”