Sound is as important to cetaceans as light is to humans. In most oceans visibility underwater is limited to a few 10s of metres and is regularly much less. In response to the challenges of using light to navigate and locate food in the ocean, cetaceans have adapted to take advantage of the physics of sound underwater. Sound travels ~4.4 times faster in sea water than in air and, all things being equal, travels ~100 times further underwater than in air. As in air, low frequency sounds travel much further underwater than high frequencies (think of the distant sound of the bass drum heard will before the rest of the marching band at the parade). If conditions are right, underwater sounds can travel thousands of kilometres across entire ocean basins – low frequency blue whale calls can travel in “deep water sound channels” that refract waves up and down allowing them to travel thousands of kilometers.