Whales can 'turn down' their hearing

Whales can "adjust" their super-sensitive hearing, used to hunt and navigate, and can turn it down when they anticipate loud noises, U.S. researchers say. Scientists at the University of Hawaii conducted a study using a trained false killer whale, or marine dolphin, named Kina. Paul Nachtigall and a colleague, Alexander Supin from the Russian Academy of Sciences, said they suspected Kina might have the ability "to control the level of her hearing." 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 as she hunted. The researchers monitored the whale's brain while they played a "neutral tone," an innocuous beep, then followed that with a 5-second pulse of 170 decibels, equivalent to the loudness of a rifle shot. Over time, they said, Kina learned this neutral tone was a warning signal and turned down her hearing sensitivity when she heard it, so the sensors recorded a smaller signal from the subsequent loud noises. Marine mammals such as dolphins, sperm whales and killer whales that use echolocation for hunting may have evolved this rapidly adjustable hearing to protect themselves from their own clicks and buzzes, Nachtigall said. "They sounds they produce are very loud -- they can be over 230-decibel pulses, and then must listen immediately for very quiet echoes," he told the BBC. "Her whole head is an ear. There are many paths for sound to travel up to her actual ears," he said.