The mammals can be taught to react like humans plugging their ears when jets fly over, researchers found in limited trials.
Perhaps we can save the whales -- or at least their hearing.
Scientists have long known that man-made underwater noises -- from engines, sonars, weapons testing, and industrial tools such as air guns used in oil and gas exploration -- are deafening whales and other sea mammals. The Navy estimates that loud booms from just its underwater listening devices, mainly sonar, result in temporary or permanent hearing loss for more than a quarter-million sea creatures every year, a number that is rising.
Now, scientists have discovered that whales can decrease the sensitivity of their hearing to protect their ears from loud noises, though they haven't pinpointed how the animals do it.
"It's equivalent to plugging your ears when a jet flies over," said Paul Nachtigall, a marine biologist at the University of Hawaii who led the discovery team. "It's like a volume control."
The finding, while preliminary, is already raising hopes for the development of warning signals that would alert whales, dolphins and other sea mammals to auditory danger.
The noise threat arises because of the basic properties of seawater. Typically, light can travel for hundreds of feet through ocean water before diminishing to nothingness. But sound can travel for hundreds of miles.
The world's oceans have been getting noisier as companies and governments expand their undersea activities. Researchers have linked the growing racket to deafness, tissue damage, mass strandings and disorientation in creatures that rely on hearing to navigate, find food and care for their young.
The latest development took place at a research facility off Oahu -- the island where the opening shots of "Gilligan's Island" were filmed.
Scientists there are studying how dolphins and toothed whales hear. In nature, the mammals emit sounds and listen for returning echoes in a sensory behavior known as echolocation. In captivity, the creatures were taught to wear suction-cup electrodes, which revealed the patterns of brainwaves involved in hearing.
The discovery came in steps. First, Nachtigall and his team found that the animals could adjust their hearing in response to their own loud sounds of echolocation, mainly sharp clicks. The scientists then wondered if the animals could also protect their ears from incoming blasts. The team focused on a false killer whale named Kina and sought to teach her a conditioned behavior similar to how Pavlov taught dogs to salivate upon hearing a bell.
First, the scientists played a gentle tone repeatedly. Then they followed the gentle pulse with a loud sound. After a few trials, the warning signal alone caused Kina to decrease the sensitivity of her hearing.
"It shows promise as a way to mitigate the effects of loud sounds," said Nachtigall.
In the future, the team plans to expand the research to other species in captivity and ultimately to animals in the wild.