Whales and dolphins can naturally muffle loud sounds

Marine mammals, like this bottlenose dolphin, can reduce their hearing sensitivity to loud sounds. Image courtesy of iStock/Madelein_Wolf via sciencemag.org.

Instead of wearing earplugs at a rock concert, imagine you could simply tune a dial inside your ears to lower the volume—and protect your hearing. Four species of whales and dolphins can do this naturally, new research reveals. This could potentially allow the animals to shield themselves from the cacophony of Navy sonar and oil drilling, which has been linked to at least 500 marine mammal deaths since 1963.

In 2008, researchers at the Hawai‘i Institute of Marine Biology (HIMB) began to suspect some marine mammals could protect their hearing naturally, at least in modest ways. The team collaborated with scientists from Russia and the Netherlands to look for this effect in a bottlenose dolphin, a harbor porpoise, and a beluga whale, in addition to extending the study on a false killer whale. The scientists measured the animals’ brain activity while hearing sounds loud enough to evoke a response, but below the threshold of causing temporary hearing loss. Each of the trained captive animals learned to reduce its hearing sensitivity by 10 to 20 decibels when the scientists played a warning signal before producing the loud sound, the researchers report in a paper in press at Integrative Zoology.

“That’s similar to a human putting in foam earplugs,” says team leader Paul Nachtigall, a marine biologist and director emeritus of the Marine Mammal Research Program at HIMB. “It’s really fascinating to be able to have that switch inside of your head.”

Read more about it at Science.