A new study published in Current Biology found that dolphins “shout” as they try to work together in response to increased underwater noise levels.

Dolphins are social and intelligent animals that rely on whistling and echolocation for hunting and breeding. This means that noise generated by human activities, such as drilling and transportation, can negatively affect the health of wild dolphin populations.

“The same reasons that make sound so beneficial to animals also make them susceptible to environmental noise,” explained first author Pernille Sorensen of the University of Bristol, UK. “Over the last two decades, we have seen a dramatic increase in human-caused noise, and ocean noise pollution is no exception,” he added.

The two dolphins observed during the study, Delta and Reese, were placed in an experimental lagoon and equipped with sound recording suction cups to document their vocalizations. They had to work together to push their own underwater button located at each end of the lagoon at one-second intervals.

During each trial, they were released from the starting point, and in some trials, one of the dolphins was held for five to 10 seconds and the other was immediately released. During the delayed release trials, the dolphins had to rely solely on vocal communication to coordinate button presses.

The researchers found that when an increased level of noise was played from the underwater speaker, both dolphins compensated by changing the volume and duration of their calls to coordinate button presses. From the lowest to the highest noise level, the dolphins’ success rate dropped from 85% to 62.5%.

Dolphins not only changed their cry, but also their body language. As the noise level increased, the dolphins changed orientation to face each other and swam to the other side of the lagoon to get closer.

“This shows us that even though they were using these compensatory mechanisms, their communication was disrupted by the noise,” Sorensen said. “Our work shows that despite their attempts to compensate by being highly motivated and well aware of this joint task, noise continued to impair their ability to successfully coordinate actions,” he added.

Although this study was conducted on dolphins living under human care, human-generated noise can also have harmful effects on wild dolphins.

“If groups of animals in the wild, for example, are less efficient at foraging together, that will have a negative impact on individual health, which will ultimately affect population health,” he said. Co-author Stephanie King, Associate Professor, University of Bristol.

“Our work shows that these adjustments are not necessarily enough to overcome the negative effects of noise on human communication,” King said.

Because dolphins depend on their communication skills for successful hunting and reproduction, noise levels can affect their behavior, which in turn affects public health.

“This collaboration with international colleagues at the Dolphin Research Center gave us a unique opportunity to study the effects of noise on animals working together in a controlled environment, which is almost impossible to do in the wild,” said Sorensen. To study this in the wild, researchers will need to better understand when animals actively work together and how cooperative behavior is coordinated.

“Our results clearly show the need to consider how noise affects group tasks in wild animals,” he concluded.