Dolphins raise voices against human din

Delta and Reese with tags attached (Dolphin Research Centre)
Delta and Reese with tags attached (Dolphin Research Centre)

Many animal species use sound to help them perform co-operative actions – but this reliance can render them vulnerable to disturbance from human noise pollution.

Now an international team of researchers led by the University of Bristol has shown how dolphins’ ability to work together is hampered by human-generated noise, which forces them to raise their voices in an effort that can be doomed to failure.

Also read: ‘Incoherent’ UK law failing whales & dolphins

The scientists used suction cups to tag two trained and “highly motivated” bottlenose dolphins called Delta and Reese in a pen at Florida’s Dolphin Research Centre. The aim was to record the two dolphins’ vocalising and movement as they participated in a task that involved each one having to press its own underwater button within a second of each other. 

The dolphins would normally co-operate to achieve the task by communicating through whistles. However, as the scientists increased the external noise level they found that Delta and Reese’s whistles grew louder and longer as they tried to compensate – and their success in performing the task decreased.

Under water the dolphins struggled to make themselves heard (Dolphin Research Centre)
Under water the dolphins struggled to make themselves heard (Dolphin Research Centre)

“For years we have known that animals can attempt to compensate for increased noise in their environment by adjusting their vocal behaviour,” said study lead author Pernille Sørensen from Bristol’s School of Biological Sciences. “Our work shows that these adjustments are not necessarily sufficient to overcome the negative impacts of noise on communication between animals working together.

“We had a unique opportunity to study the negative effects of noise on co-operative behaviour in a controlled setting, something that is almost impossible to do in the wild. Our findings clearly highlight the need to account for how noise affects group tasks in wild animals.”

“It also shows us that dolphins can flexibly modify their vocalisations in an attempt to continue co-operating with their partner, revealing that this species is capable of actively co-ordinated collaboration,” added senior author Dr Stephanie King, associate professor in animal behaviour at the school.

“We show that human-made noise directly affects the success of animals working together. If noise makes groups of wild animals less efficient at performing co-operative actions, such as co-operative foraging, then this could have important negative consequences for individual health, and ultimately population health.”

The paper is published in Current Biology.

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