Recently, a scuba diver was treated not to a rare sighting of an unusual fish or marine creature but to the sounds of humpback whales singing loudly as he dived below the waves off Oahu, Hawaii.

“It was the loudest/most whales I’ve heard singing underwater so I decided to send a GoPro down so I could show people,” Mark Healey, who filmed the video, told Storyful.

Humpbacks produce these incredible sounds by using their vocal cords, which rub against a cushion of fat at the back of their throats. While both male and female humpbacks are capable of making noises, only the male humpbacks sing loud, elaborate songs to attract a mate. 

Even the calves get in on the action with research showing that they make vocalizations that seem to be them begging their mothers for milk. “The calf makes different social calls, like long, low grunts, short whoops, and high-pitched whines, but when it comes to nursing, the calls are usually short, low-frequency sounds that kind of resemble barks or burps,” study lead and postdoctoral researcher Maevatiana Nokoloina Ratsimbazafindranahaka told IFLScience last year.

Whale song was also recently found to follow one of the fundamental rules of human language, Zipf’s law, meaning that while the whales might be yapping away down under the waves, they aren’t wasting any notes and have an efficient language system. 

According to NOAA every year up to 12,000 humpbacks travel to the warmer waters off the coast of Hawaii’s islands to find a mate and raise their young. From November to May, these gentle ocean giants spend time around these islands with members of the public taking the opportunity to spot them.