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Scientists believe beluga whales make shapes with the squishy bit of fat on their foreheads to talk to each other.

Sometimes called the 'canaries of the sea', belugas are known for communicating through noises like whistles, squeals and clicks.

But researchers have found that they also make five distinct shapes with their foreheads while socialising - almost like facial expressions.

They can move their melon (the name for the bulb of fat on their heads) in many ways - from squashing it down against their skull to shaking it so it jiggles like jelly.

Researchers observed the whales for over a year and created a beluga 'vocabulary' - naming the different head shapes: flat, lift, press, push and shake.

The belugas squashed and jiggled their foreheads most often when trying to attract a mate.

One of the researchers first spotted the whales making shapes with their melon while working as a beluga trainer at an aquarium.

"Even as a trainer, I knew the shapes meant something," said animal behaviourist Justin Richard.

"But nobody had been able to put together enough observations to make sense of it."

His team watched how four belugas in captivity acted around each other, and found that they made two shapes per minute on average.

It isn't clear if the whales make these shapes on purpose - but the scientists found the creatures almost always made them when a friend could see them.

Afterwards, the experts looked at a larger group of 51 whales and found they made the exact same shapes.

The scientists are excited about finding out how the creatures move their melons in the wild, and how this interacts with their famous whistles and clicks.