Low
frequency sound waves travel a long distance in water and humpback whales can
communicate over very long distances. Dolphins and toothed whales produce short
bursts of sound that they focus into a directional beam using their bulbous
forehead. They use this for echolocation of fish, but the sounds can be very
loud and disturbing if you are nearby – 230 decibels would be uncomfortable up
close.
The
reflection from a fish for dinner some distance away will be very quiet, so how
come these mammals don’t deafen each other when they are in a group looking for
dinner?
Well,
I didn’t hear the buzz about this that was presented by Nachtigall and Supin at
Acoustics 2012 (1) who had asked and solved this question with their
well-behaved friend Kina, a false killer whale, by checking out her brain
activity when the made some noises. The BBC have reviewed their presentation
(2).
They
made noises which were quietly innocuous and increased the beeps to 170
decibels which would make me duck and run for cover. Kina’s brain activity
increased in proportion to the decibel rating, but they found that if they played a quiet sound just prior to the very loud one, she figured out what was
coming and turned the volume down on her ears as they figured out from her
brain activity dropping proportionately. She has a sort of whales mute button.
Not
quite the complete mute button like our teenagers seenm to activate when we ask them to
tidy their rooms.
