Noisy Environment.

Dolphins raising their voices

to be heard over human din.

Mammals in the ocean swim through a noisy world. But in recent decades, humans have cranked up the volume, blasting waters with the sounds of shipping, oil exploration and other operations.

New research suggests such noise may make it. harder for dolphins to communicate and work together.

When dolphins cooperated on a task in a noisy environment, they behaved like city dwellers trying to be heard over a din of jackhammers and sirens : They yelled, researchers reported in the journal Current Biology.

Dolphins hunt together, using sound to communicate and to keep their families together. A noisy environment could affect their feeding and their ability to reproduce, said an expert who wasn't part of the study.

The scientists who produced the report worked with two dolphins trained to push buttons simultaneously. The dolphins whistled to each other, sometimes apparently signaling right before pressing their button.

Then the researchers piped in sounds, using underwater speakers.

To compensate for the loud noise, the dolphins turned their bodies toward each other, and each paid more attention to the other's location. At times, they amplified their whistles - in a sense shouting.

But the noiser it got, the less successful they were at their tasks. At peak volume, they succeeded 62.5 percent of the time - about 20 percent less than at ambient sound levels. [ Carolyn Wilke ]


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