http://news.bbc.co.uk/2/hi/science/nature/7641537.stm ---Clicks are generated when a structure just below the blowhole known as "monkey's lips" smacks together.That generates a wave radiating spherically outwards, which is transformed into a directionally forward-focussed plane wave as it passes through a fat "melon" - an acoustic lens.So the sound - too high-pitched for a human to hear - shoots out in front of the whale, and if it hits food, such as a squid, a portion is reflected.The reflection was thought to travel to the whale's ears, via its lower jawbone. But the scan suggested a more important route is under the bone.Top of head for transmitting, bottom of head for receiving; a neat system.The sound reception part appears to be very complex, involving fat bodies that focus sound and air sacs that reflect it."Air sacs are perfect acoustic mirrors," says Ted Cranford."The whales need to be able to isolate their ears from each other in order to maintain their directional sense, and one of the best ways to do that is through air sacs."
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