If you stand on certain shorelines and listen carefully you might just hear deep rumbling noises. Sharp-eared fishers, lighthouse keepers and sea kayakers have been haunted by these late-night sounds for centuries and now, for the first time, scientists have recorded these thrums and pinpointed them to humpback whales, proving that whales have a far larger vocabulary than previously thought.

Fred Sharpe from the Alaska Whale Foundation and his colleagues set up land-based microphones to tune in to the mysterious ocean noises. Tip-offs from Alaskan coastal communities helped to narrow down the best recording locations. Along with the previously documented trumpets, blows and shrieks that humpback whales make, the researchers recorded very low frequency rumbles, a bit like distant thunder, and new sounds including pizzle, howl and hooting noises. The night thrums travelled through the air and could be heard up to 6 miles (10km) away.

Sharpe, who presented his findings at the Astrobiology Science Conference in Madison, Wisconsin, on 18 May, postulates that the thrums may emanate from special structures in the whale’s blowhole, which prevent water going in when they dive. Understanding these sounds could help to prevent whales being hit by ships. They could also help inform how we overcome perceptual biases and design systems to search for intelligent extraterrestrial life.