Dolphins raise voices to communicate in noisy waters

When their water environment becomes noisy, dolphins put in extra effort, raising their voices in order to communicate.

The findings are of a new research by scientists at NOAA Fisheries' Northwest Fisheries Science Center and the University of California Santa Cruz, that for the first time measures the biological costs to marine mammals of trying to communicate over the sounds of ship traffic or other sources.

Lead author Marla Holt said that if they're repeatedly exposed to a lot of noise, the repeated effort to call louder or longer or more often, that was where the impacts could become more significant.

The report also noted that ship noise can interfere with the echolocation the whales use to locate and hunt for food. The new findings suggest that consistently noisy surroundings could take a toll on marine mammals that rely on calls for basic life functions such as communication and foraging.

The research examined the energy expenditures of trained captive dolphins at UC Santa Cruz as stand-ins for killer whales, since the species produce sound in similar ways. The dolphins were trained to whistle softly as they might in quiet conditions and more loudly as they would in situations with greater background noise. Plastic hoods over the dolphins measured their oxygen consumption as a gauge of how much energy they expended in producing the whistles of different volumes.

The study found that the dolphins consumed about 80 percent more oxygen when whistling at the highest vocal energy levels than they did at rest. Dolphins have been found to whistle at higher repetition rates when boats are approaching, a behavior that is predicted to expended more energy based on the study's results. The results are consistent with other similar studies on birds and humans that also found similar increases in oxygen consumption associated with longer, more frequent and louder calls.

The paper is published in the Journal of Experimental Biology.