Video: You've probably watched enough documentaries to know that humpback whales communicate using clicks and whistles. But put on a pair of headphones and listen to the video above. Beneath the shrill chatter we've all heard before, there's a much lower-pitched tone, eerily reminiscent of a human heartbeat. A touch above the limit of human hearing, these deep "pulse trains" were recorded for the first time near the Hawaiian island of Maui, where thousands of whales meet up each winter to mate and give birth. Scientists aren't yet sure what the low tones mean -- but the whales themselves may offer a clue. Pulse trains almost always occur when adult females are in the company of males.
Perhaps, this haunting beat is the sound of whales in love.