Beluga Whales May Change The Shape Of Their Squishy Melons To Communicate

Communication comes in all forms in the natural world. African elephants may use names, while bats prefer death metal growls – but not all communication is vocal. Belugas (Delphinapterus leucas), for example, may be able to express themselves using their squishy foreheads, known as melons.

Melons are made up of fatty tissue and are found in all toothed whales. They help modulate the animals' vocalizations, essentially acting as a lens for better communication and echolocation. But they may also have a visual purpose.

“Beluga whales are considered unique among [toothed whales] in their ability to visibly alter the appearance of their head by changing the shape of the melon,” write the authors of the new study. However, until now, only anecdotal evidence existed to explain the potential function of these shapes.

To investigate further, the team observed belugas in captivity, identifying a total of 2,570 melon shapes from videos of four whales. These shapes could then be whittled down to five different types: flat, lift, press, push, and shake. Additional observations in a second aquarium population of 51 whales backed this finding up.

Flat melons, as you might expect, are flattened at the front, eliminating the normal rounded shape. Lifted melons, meanwhile, are raised and appear taller. When the melon is pressed, it is squashed along the top of the skull, looking more boxy in shape. In comparison, a pushed melon is pushed forward, appearing more bulbous, and finally, during a shake, it wobbles up and down.

The researchers also found that melon shapes occurred 34 times more frequently during social interactions than outside of them. "Melon shapes occurring during social interactions were performed within the line of sight of a recipient 93.6 percent of the time," they add.

Males changed the shapes of their melons more than three times as frequently as females, and the shapes varied by behavioral context. Courtship, for example, was associated with higher-than-expected rates of melon shapes, particularly shake. Whereas, mouthing and open-mouth interactions, including biting and raking, were more likely to involve push.

It’s not totally clear whether these strange shapes are intentional, and, if they are, what each one may mean, but the team thinks there’s a chance that belugas are using them to communicate with one another.

"Melon shapes seem to function as visual displays, with some characteristics of intentional communication," they write. "This ability could yield adaptive benefits to belugas, given their complex social structure and hypothesized mating system that emphasizes pre-copulatory female mate choice."

However, they also highlight some limitations in their study. Namely, the small sample size and limited behavioral and social contexts observed.

Nonetheless, the findings highlight just how much we still have to learn about communication in belugas, and open up interesting avenues for future research.

The study is published in Animal Cognition.