A Whales Mute Button

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.

  1. http://acoustics2012hk.org/abstract_detail.php?number=4aAB3
  2. http://www.bbc.co.uk/nature/18085158

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