Belugas May Communicate by Changing the Shape of Their Squishy Foreheads

Scientists documented five different melon shapes among the marine mammals living in captivity: push, flat, lift, shake and press

Belugas swimming underwater
Male belugas were more likely than females to change the shape of their melons, or foreheads. Mike Johnston via Flickr under CC BY 2.0

Belugas are known as the “canaries of the sea,” because they make a wide array of sounds to communicate—from chirps and whistles to clicks and squeals.

As they chatter away, these charismatic marine mammals are also contorting their foreheads into different shapes, researchers recently reported in the journal Animal Cognition.

More specifically, scientists have identified five unique shapes that belugas make with the melon, the name for the fatty deposit on the front of their heads. The toothed whales can push the melon forward, flatten it, shake it, press it and lift it, according to the paper.

Researchers who study belugas have long noticed the creatures making these different melon shapes. But the paper systematically documents them and provides broader context for how often they occur and under what circumstances. The study’s co-authors have created a running list of beluga vocabulary that other researchers can now use and, likely, build upon.

“Even as a trainer, I knew the shapes meant something,” says study co-author Justin Richard, an animal behaviorist at the University of Rhode Island who used to work as a beluga trainer, to Science News’ Elizabeth Anne Brown. “But nobody had been able to put together enough observations to make sense of it.”

Belugas changing the shape of their melons during social interactions

Belugas (Delphinapterus leucas) are social marine mammals that live in Arctic and sub-Arctic waters, including off the coast of Alaska. On average, they weigh 3,150 pounds and can measure up to 16 feet long.

While belugas can live for up to 90 years, they’re susceptible to many threats, including disease and predation from orcas. They’re affected by several types of human disturbances, including fisheries, shipping, oil and gas exploration and climate change.

Belugas belong to a group known as toothed whales, which also includes orcas, dolphins and sperm whales—and all members of this group have melons. But while these species all possess muscles that could likely contort their melons in various ways, per the paper, the beluga is the only one that scientists have seen using this behavior.

For the study, researchers captured the different melon shapes on video while filming four belugas at Mystic Aquarium in Connecticut between 2013 and 2014. Then, they confirmed their initial observations by watching 51 belugas at MarineLand Canada in Niagara Falls.

In total, the researchers observed 2,570 melon shapes with the group at Mystic Aquarium, plus another 72 melon shapes at MarineLand Canada. These broadly fit into their five shape categories.

Triptych of beluga whale in water
Scientists are still piecing together why belugas change the shape of their melons, but they suspect it's a form of communication. Richard et al. / Animal Cognition, 2024

Researchers don’t know exactly what each shape means. But after carefully watching the marine mammals, they’ve developed a few theories. For starters, they believe belugas are making the shapes to communicate with each other, because 93.6 percent of melon shapes occurred when a beluga was within the line of sight of another beluga. They made nearly two shapes per minute while interacting with other members of their species.

“Melon shapes occurred 34 [times] more frequently during social interactions… than outside of social interactions,” the team writes in the paper.

They also noticed some patterns in the shapes. For example, shaking and pressing seem to be linked with courtship and sexual behavior. Other motions—such as flattening and lifting—did not appear to be linked with any particular behavior and were more challenging to translate, which might suggest “more flexible usage,” the researchers write.

Males were also much more likely than females to change the shapes of their melons: Males made between 1.3 and 1.34 shapes per minute while interacting with other belugas, while females made 0.38 shapes per minute while socializing.

Scientists have previously found that belugas use their melons for echolocation, which allows them to “see” underwater. But the idea that their fatty foreheads could be used for communication adds another piece to the puzzle.

“At present, we have no idea if there is a trade-off between these functions,” Ellen Coombs, a cetacean researcher at Smithsonian’s National Museum of Natural History who was not involved in the study, tells Smithsonian magazine in an email. “For example, are belugas able to vocalize/echolocate whilst performing these visual displays? Does one function enhance or hinder the other?”

“This could prompt further study of the function of the melon, not only in belugas, but in other toothed whales,” Coombs adds.

For now, researchers have only documented the behavior among captive belugas. It’s not clear whether belugas in the wild also change the shape of their melons, nor whether the shapes have the same meaning in the two different settings.

Another lingering question is whether the belugas are making shapes on purpose, or whether this behavior is merely a reflex that reflects their mood, per Science News. Based on the recent findings, though, researchers suspect the behavior is intentional and represents another form of communication.

“Findings like these, that give us insight into social interactions, complex behavior, et cetera, have implications for conservation and management,” Coombs says. “It all enhances a body of knowledge required to better understanding these complex animals.”

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