The songs can last up to 20 minutes, and can be heard more than 20 miles away. Song patterns can change gradually over time, so that new songs emerge every few years. Researchers still aren't sure exactly how the whales produce the sounds. Whales don't have vocal cords, so they probably sing by circulating air through the tubes and chambers of their respiratory system. The meaning of whale songs is widely debated.
Scientists are also unsure about what the songs mean.
Originally, observers believed they were a mating call, used to advertise the male's availability to passing females. This idea was reinforced when divers observed other whales approaching the singers. More recently, however, some researchers have come to believe that the singing humpbacks are actually issuing threats, not singing love songs. In part, that idea arose because scientists discovered that many of the whales approaching singers were other males, and the meeting would often end in a tussle. Another recent theory is that the singing whales are simply finding out who is in the neighborhood, using the songs as a form of sonar for tracking nearby whales.