London: For the first time, scientists have discovered that whales can adjust their hearing to navigate and hunt better, a finding which they say could help improve protection of wild marine mammals.
Researchers from the the University of Hawaii measured the hearing of a female false killer whale, called Kina, and found that she could fine-tune her most crucial sense.
She would "turn down" her hearing when she anticipated a loud noise, said Dr Paul Nachtigall, who led research.
"Her whole head is an ear. There are many paths for sound to travel up to her actual ears," Dr Nachtigall said.
False killer whales belong to a group of species known as "toothed whales, which includes dolphins, sperm whales and killer whales. These mammals hunt using echolocation -- producing high-frequency buzzing or clicking sounds and decoding the echoes they produce to locate prey.
To study Kina`s hearing, the researchers, who first noticed five years ago that Kina might have the ability "to control the level of her hearing, needed an insight into what was happening inside her head.
They placed sensors contained within soft latex suction cups on Kina`s body to measure the electrical activity in Kina`s brain as it responded to sound.
"Louder sounds make big brain waves, quieter sounds make smaller waves," said Dr Nachtigall. "[And] if she does not hear the sound we do not see the pattern."
The researchers, who presented their findings at the Acoustics 2012 meeting in Hong Kong, played Kina a "neutral tone" -- an innocuous bleep -- then followed that with a five-second pulse of 170 decibels. That is equivalent in intensity to the sound of a rifle being fired one metre away.
Over time, Kina learned that this neutral tone was a warning signal and turned down her hearing sensitivity when she heard it, so in subsequent experiments, the sensors recorded a smaller signal from a noise of the same loudness.
Dr Nachtigall explained that echolocating marine mammals may have evolved this rapidly adjustable hearing to protect themselves from their own clicks and buzzes.
"They sounds they produce are very loud -- they can be over 230-decibel pulses, and then must listen immediately for very quiet echoes," Dr Nachtigall said.
The team hopes that their findings will eventually be applied to the protection of wild marine mammals.
There is evidence that whales and dolphins are disturbed or damaged by man-made undersea noise, such as naval sonar and the loud seismic airguns used in oil and gas exploration.
"This makes us very optimistic that many echolocating porpoises dolphins and whales will be able to change their hearing to protect it if they are properly warned," said Dr Nachtigall.
"We want to define the proper way to warn them."