New research shows that dolphins roar at each other due to increased levels of underwater noise pollution.
Humans may be forcing animals to whistle louder and less effectively, according to experts at the University of Bristol.
Dolphins rely on echolocation to hunt and reproduce, which means activities such as drilling and shipping could affect the health of wild dolphin populations.
“Over the past few decades, we’ve seen a dramatic increase in anthropogenic noise, and noise pollution in the ocean is no exception,” said first author Pernille Sorensen.
“The same reasons that make animals’ use of sound so beneficial also make them vulnerable to environmental noise,” she added.
Researchers put two dolphins, named Delta and Reese, in an experimental lagoon where they had to work together to press buttons on each end within a second.
In some trials, one dolphin was released 5 to 10 seconds later than the other, meaning they had to rely on vocal communication to coordinate button presses.
The researchers found that both Delta and Reese changed the volume and length of calls when they increased the level of noise played through the underwater speakers.
The study found that their button press success rates dropped from 85 percent to 62.5 percent between the lowest and highest noise levels.
Despite high positivity, dolphin communication is impaired by noise
Ms Sorensen said: “This shows us that despite their use of these compensatory mechanisms, their communication is affected by the noise.
“Our work shows that despite their attempts to compensate, despite their high motivation and their excellent understanding of this cooperative task, noise still impairs their ability to coordinate successfully.”
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As the speaker volume was increased, the dolphins were also more likely to face each other or swim to the other side of the lagoon to get closer.
read more: Russia ‘deploys highly trained military dolphins at naval base’
Although the study was conducted on dolphins living in human care, the researchers say human-made noise could have adverse effects on wild dolphins.
Co-author Stephanie King, Associate Professor at the University of Bristol, said: “For example, if groups of animals in the wild are less efficient at cooperating to forage for food, then this will have a negative impact on individual health and ultimately population health”
The study was published in the journal Current Biology.